Tree View Tutorial

This is a tutorial on how to use the GTK GtkTreeView widget through its C interface.

This tutorial is based on the GTK 2.0 Tree View Tutorial by Tim-Philipp Müller.

Lists and Trees: the GtkTreeView Widget

GtkTreeView is a widget that displays single- or multi-columned lists and trees. It replaces the old GTK 1.2 GtkCList and GtkCTree widgets. Even though GtkTreeView is slightly harder to master than its predecessors, it is so much more powerful and flexible that most application developers will not want to miss it once they have come to know it.

The purpose of this chapter is not to provide an exhaustive documentation of GtkTreeView—that is what the API documentation is for, which should be read alongside with this tutorial. The goal is rather to present an introduction to the most commonly-used aspects of GtkTreeView, and to demonstrate how the various GtkTreeView components and concepts work together. Furthermore, an attempt has been made to shed some light on custom tree models and custom cell renderers, which seem to be often-mentioned, but rarely explained.

Developers looking for a quick and dirty introduction that teaches them everything they need to know in less than five paragraphs will not find it here. In the author’s experience, developers who do not understand how the tree view and the models work together will run into problems once they try to modify the given examples, whereas developers who have worked with other toolkits that employ the Model/View/Controller-design will find that the API reference provides all the information they need to know in more condensed form anyway. Those who disagree may jump straight to the working example code of course.

Please note that the code examples in the following sections do not necessarily demonstrate how GtkTreeView is used best in a particular situation. There are different ways to achieve the same result, and the examples merely show those different ways, so that developers are able to decide which one is most suitable for the task at hand.

Hello World

For the impatient, here is a small tree view ‘Hello World’ program:

#include <gtk/gtk.h>

enum
{
  COL_NAME = 0,
  COL_AGE,
  NUM_COLS
} ;


static GtkTreeModel *
create_and_fill_model (void)
{
  GtkListStore *store = gtk_list_store_new (NUM_COLS,
                                            G_TYPE_STRING,
                                            G_TYPE_UINT);

  /* Append a row and fill in some data */
  GtkTreeIter iter;
  gtk_list_store_append (store, &iter);
  gtk_list_store_set (store, &iter,
                      COL_NAME, "Heinz El-Mann",
                      COL_AGE, 51,
                      -1);

  /* append another row and fill in some data */
  gtk_list_store_append (store, &iter);
  gtk_list_store_set (store, &iter,
                      COL_NAME, "Jane Doe",
                      COL_AGE, 23,
                      -1);

  /* ... and a third row */
  gtk_list_store_append (store, &iter);
  gtk_list_store_set (store, &iter,
                      COL_NAME, "Joe Bungop",
                      COL_AGE, 91,
                      -1);

  return GTK_TREE_MODEL (store);
}

static GtkWidget *
create_view_and_model (void)
{
  GtkWidget *view = gtk_tree_view_new ();

  GtkCellRenderer *renderer;

  /* --- Column #1 --- */
  renderer = gtk_cell_renderer_text_new ();
  gtk_tree_view_insert_column_with_attributes (GTK_TREE_VIEW (view),
                                               -1,      
                                               "Name",  
                                               renderer,
                                               "text", COL_NAME,
                                               NULL);

  /* --- Column #2 --- */
  renderer = gtk_cell_renderer_text_new ();
  gtk_tree_view_insert_column_with_attributes (GTK_TREE_VIEW (view),
                                               -1,      
                                               "Age",  
                                               renderer,
                                               "text", COL_AGE,
                                               NULL);

  GtkTreeModel *model = create_and_fill_model ();

  gtk_tree_view_set_model (GTK_TREE_VIEW (view), model);

  /* The tree view has acquired its own reference to the
   *  model, so we can drop ours. That way the model will
   *  be freed automatically when the tree view is destroyed
   */
  g_object_unref (model);

  return view;
}

int
main (int argc, char **argv)
{
  gtk_init (&argc, &argv);

  GtkWidget *window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  g_signal_connect (window, "destroy", gtk_main_quit, NULL);

  GtkWidget *view = create_view_and_model ();

  gtk_container_add (GTK_CONTAINER (window), view);

  gtk_widget_show_all (window);

  gtk_main ();

  return 0;
}

Components: Model, Renderer, Column, View

The most important concept underlying GtkTreeView is that of complete separation between data and how that data is displayed on the screen. This is commonly known as Model/View/Controller-design (MVC). Data of various type (strings, numbers, images, etc.) is stored in a ‘model’. The ‘view’ is then told which data to display, where to display it, and how to display it. One of the advantages of this approach is that you can have multiple views that display the same data (a directory tree for example) in different ways, or in the same way multiple times, with only one copy of the underlying data. This avoids duplication of data and programming effort if the same data is re-used in different contexts. Also, when the data in the model is updated, all views automatically get updated as well.

So, while GtkTreeModel is used to store data, there are other components that determine which data is displayed in the GtkTreeView and how it is displayed. These components are GtkTreeViewColumn and GtkCellRenderer. A GtkTreeView is made up of tree view columns. These are the columns that users perceive as columns. They have a clickable column header with a column title that can be hidden, and can be resized and sorted. Tree view columns do not display any data, they are only used as a device to represent the user-side of the tree view (sorting etc.) and serve as packing widgets for the components that do the actual rendering of data onto the screen, namely the GtkCellRenderer family of objects (I call them ‘objects’ because they do not inherit from GtkWidget). There are a number of different cell renderers that specialise in rendering certain data like strings, pixbufs, or toggle buttons. More on this later.

Cell renderers are packed into tree view columns to display data. A tree view column needs to contain at least one cell renderer, but can contain multiple cell renderers. For example, if one wanted to display a ‘Filename’ column where each filename has a little icon on the left indicating the file type, one would pack a GtkCellRendererPixbuf and a GtkCellRendererText into one tree view column. Packing renderers into a tree view column is similar to packing widgets into a GtkBox.

Models for Data Storage: GtkListStore and GtkTreeStore

It is important to realise what GtkTreeModel is and what it is not. GtkTreeModel is basically just an ‘interface’ to the data store, meaning that it is a standardised set of functions that allows a GtkTreeView widget (and the application programmer) to query certain characteristics of a data store, for example how many rows there are, which rows have children, and how many children a particular row has. It also provides functions to retrieve data from the data store, and tell the tree view what type of data is stored in the model. Every data store must implement the GtkTreeModel interface and provide these functions, which you can use by casting a store to a tree model with GTK_TREE_MODEL(store). GtkTreeModel itself only provides a way to query a data store’s characteristics and to retrieve existing data, it does not provide a way to remove or add rows to the store or put data into the store. This is done using the specific store’s functions.

GTK comes with two built-in data stores (models): GtkListStore and GtkTreeStore. As the names imply, GtkListStore is used for simple lists of data items where items have no hierarchical parent-child relationships, and GtkTreeStore is used for tree-like data structures, where items can have parent-child relationships. A list of files in a directory would be an example of a simple list structure, whereas a directory tree is an example for a tree structure. A list is basically just a special case of a tree with none of the items having any children, so one could use a tree store to maintain a simple list of items as well. The only reason GtkListStore exists is in order to provide an easier interface that does not need to cater for child-parent relationships, and because a simple list model can be optimised for the special case where no children exist, which makes it faster and more efficient.

GtkListStore and GtkTreeStore should cater for most types of data an application developer might want to display in a GtkTreeView. However, it should be noted that GtkListStore and GtkTreeStore have been designed with flexibility in mind. If you plan to store a lot of data, or have a large number of rows, you should consider implementing your own custom model that stores and manipulates data your own way and implements the GtkTreeModel interface. This will not only be more efficient, but probably also lead to saner code in the long run, and give you more control over your data. See below for more details on how to implement custom models.

Tree model implementations like GtkListStore and GtkTreeStore will take care of the view side for you once you have configured the GtkTreeView to display what you want. If you change data in the store, the model will notify the tree view and your data display will be updated. If you add or remove rows, the model will also notify the store, and your row will appear in or disappear from the view as well.

How Data is Organised in a Store

A model (data store) has model columns and rows. While a tree view will display each row in the model as a row in the view, the model’s columns are not to be confused with a view’s columns. A model column represents a certain data field of an item that has a fixed data type. You need to know what kind of data you want to store when you create a list store or a tree store, as you can not add new fields later on.

For example, we might want to display a list of files. We would create a list store with two fields: a field that stores the filename (i.e. a string) and a field that stores the file size (i.e. an unsigned integer). The filename would be stored in column 0 of the model, and the file size would be stored in column 1 of the model. For each file we would add a row to the list store, and set the row’s fields to the filename and the file size.

The GLib type system (GType) is used to indicate what type of data is stored in a model column. These are the most commonly used types:

  • G_TYPE_BOOLEAN
  • G_TYPE_INT, G_TYPE_UINT
  • G_TYPE_LONG, G_TYPE_ULONG, G_TYPE_INT64, G_TYPE_UINT64
  • G_TYPE_FLOAT, G_TYPE_DOUBLE
  • G_TYPE_STRING - stores a string in the store (makes a copy of the original string)
  • G_TYPE_POINTER - stores a pointer value (does not copy any data into the store, just stores the pointer value!)
  • G_TYPE_OBJECT, GDK_TYPE_PIXBUF - stores an object in the store (acquires a reference on the object instance)

You do not need to understand the type system, it will usually suffice to know the above types, so you can tell a list store or tree store what kind of data you want to store. Advanced users can derive their own types from the fundamental GLib types. For simple structures you could register a new boxed type for example, but that is usually not necessary. G_TYPE_POINTER will often do as well, you will just need to take care of memory allocation and freeing yourself then.

Storing GObject-derived types (most GDK_TYPE_FOO and GTK_TYPE_FOO) is a special case that is dealt with further below.

Here is an example of how to create a list store:

GtkListStore *list_store;

list_store = gtk_list_store_new (2, G_TYPE_STRING, G_TYPE_UINT);

This creates a new list store with two columns. Column 0 stores a string and column 1 stores an unsigned integer for each row. At this point the model has no rows yet of course. Before we start to add rows, let’s have a look at the different ways used to refer to a particular row.

GtkTreeIter, GtkTreePath, GtkTreeRowReference

There are different ways to refer to a specific row. The two you will have to deal with are GtkTreeIter and GtkTreePath.

GtkTreePath

A GtkTreePath is a comparatively straight-forward way to describe the logical position of a row in the model. As a GtkTreeView always displays all rows in a model, a tree path always describes the same row in both model and view.

The picture shows the tree path in string form next to the label. Basically, it just counts the children from the imaginary root of the tree view. An empty tree path string would specify that imaginary invisible root. Now ‘Songs’ is the first child (from the root) and thus its tree path is just “0”. ‘Videos’ is the second child from the root, and its tree path is “1”. ‘oggs’ is the second child of the first item from the root, so its tree path is “0:1”. So you just count your way down from the root to the row in question, and you get your tree path.

To clarify this, a tree path of “3:9:4:1” would basically mean in human language (attention - this is not what it really means!) something along the lines of: go to the 3rd top-level row. Now go to the 9th child of that row. Proceed to the 4th child of the previous row. Then continue to the 1st child of that. Now you are at the row this tree path describes. This is not what it means for GTK though. While humans start counting at 1, computers usually start counting at 0. So the real meaning of the tree path “3:9:4:1” is: Go to the 4th top-level row. Then go to the 10th child of that row. Pick the 5th child of that row. Then proceed to the 2nd child of the previous row. Now you are at the row this tree path describes. :)

The implication of this way of referring to rows is as follows: if you insert or delete rows in the middle or if the rows are resorted, a tree path might suddenly refer to a completely different row than it referred to before the insertion/deletion/resorting. This is important to keep in mind. (See the section on GtkTreeRowReferences below for a tree path that keeps updating itself to make sure it always refers to the same row when the model changes).

This effect becomes apparent if you imagine what would happen if we were to delete the row entitled ‘funny clips’ from the tree in the above picture. The row ‘movie trailers’ would suddenly be the first and only child of ‘clips’, and be described by the tree path that formerly belonged to ‘funny clips’, ie. “1:0:0”.

You can get a new GtkTreePath from a path in string form using gtk_tree_path_new_from_string(), and you can convert a given GtkTreePath into its string notation with gtk_tree_path_to_string(). Usually you will rarely have to handle the string notation, it is described here merely to demonstrate the concept of tree paths.

Instead of the string notation, GtkTreePath uses an integer array internally. You can get the depth (i.e. the nesting level) of a tree path with gtk_tree_path_get_depth(). A depth of 0 is the imaginary invisible root node of the tree view and model. A depth of 1 means that the tree path describes a top-level row. As lists are just trees without child nodes, all rows in a list always have tree paths of depth 1. gtk_tree_path_get_indices() returns the internal integer array of a tree path. You will rarely need to operate with those either.

If you operate with tree paths, you are most likely to use a given tree path, and use functions like gtk_tree_path_up(), gtk_tree_path_down(), gtk_tree_path_next(), gtk_tree_path_prev(), gtk_tree_path_is_ancestor(), or gtk_tree_path_is_descendant(). Note that this way you can construct and operate on tree paths that refer to rows that do not exist in model or view! The only way to check whether a path is valid for a specific model (i.e. the row described by the path exists) is to convert the path into an iterator using gtk_tree_model_get_iter().

GtkTreePath is an opaque structure, with its details hidden from the compiler. If you need to make a copy of a tree path, use gtk_tree_path_copy().

GtkTreeIter

Another way to refer to a row in a list or tree is GtkTreeIter. A tree iter is just a structure that contains a couple of pointers that mean something to the model you are using. Tree iters are used internally by models, and they often contain a direct pointer to the internal data of the row in question. You should never look at the content of a tree iter and you must not modify it directly either.

All tree models (and therefore also GtkListStore and GtkTreeStore) must support the GtkTreeModel functions that operate on tree iters (e.g. get the tree iter for the first child of the row specified by a given tree iter, get the first row in the list/tree, get the n-th child of a given iter etc.). Some of these functions are:

  • gtk_tree_model_get_iter_first(): sets the given iter to the first top-level item in the list or tree
  • gtk_tree_model_iter_next(): sets the given iter to the next item at the current level in a list or tree.
  • gtk_tree_model_iter_children(): sets the first given iter to the first child of the row referenced by the second iter (not very useful for lists, mostly useful for trees).
  • gtk_tree_model_iter_n_children(): returns the number of children the row referenced by the provided iter has. If you pass NULL instead of a pointer to an iter structure, this function will return the number of top-level rows. You can also use this function to count the number of items in a list store.
  • gtk_tree_model_iter_nth_child(): sets the first iter to the n-th child of the row referenced by the second iter. If you pass NULL instead of a pointer to an iter structure as the second iter, you can get the first iter set to the n-th row of a list.
  • gtk_tree_model_iter_parent(): sets the first iter to the parent of the row referenced by the second iter (does nothing for lists, only useful for trees).

Almost all of those functions return TRUE if the requested operation succeeded, and return FALSE otherwise. There are more functions that operate on iters. Check out the GtkTreeModel API reference for details.

You might notice that there is no gtk_tree_model_iter_prev(). This is unlikely to be implemented for a variety of reasons. It should be fairly simple to write a helper function that provides this functionality though once you have read this section.

Tree iters are used to retrieve data from the store, and to put data into the store. You also get a tree iter as result if you add a new row to the store using gtk_list_store_append() or gtk_tree_store_append().

Tree iters are often only valid for a short time, and might become invalid if the store changes with some models. It is therefore usually a bad idea to store tree iters, unless you really know what you are doing. You can use gtk_tree_model_get_flags() to get a model’s flags, and check whether the GTK_TREE_MODEL_ITERS_PERSIST flag is set (in which case a tree iter will be valid as long as a row exists), yet still it is not advisable to store iter structures unless you really mean to do that. There is a better way to keep track of a row over time: GtkTreeRowReference.

GtkTreeRowReference

A GtkTreeRowReference is basically an object that takes a tree path, and watches a model for changes. If anything changes, like rows getting inserted or removed, or rows getting re-ordered, the tree row reference object will keep the given tree path up to date, so that it always points to the same row as before. In case the given row is removed, the tree row reference will become invalid.

A new tree row reference can be created with gtk_tree_row_reference_new(), given a model and a tree path. After that, the tree row reference will keep updating the path whenever the model changes. The current tree path of the row originally refered to when the tree row reference was created can be retrieved with gtk_tree_row_reference_get_path(). If the row has been deleted, NULL will be returned instead of of a tree path. The tree path returned is a copy, so it will need to be freed with gtk_tree_path_free() when it is no longer needed.

You can check whether the row referenced still exists with gtk_tree_row_reference_valid(), and free it with when no longer needed.

For the curious: internally, the tree row reference connects to the tree model’s “row-inserted”, “row-deleted”, and “rows-reordered” signals and updates its internal tree path whenever something happened to the model that affects the position of the referenced row.

Note that using tree row references entails a small overhead. This is hardly significant for 99.9% of all applications out there, but when you have multiple thousands of rows and/or row references, this might be something to keep in mind (because whenever rows are inserted, removed, or reordered, a signal will be sent out and processed for each row reference).

If you have read the tutorial only up to here so far, it is hard to explain really what tree row references are good for. An example where tree row references come in handy can be found further below in the section on removing multiple rows in one go.

In practice, a programmer can either use tree row references to keep track of rows over time, or store tree iters directly (if, and only if, the model has persistent iters). Both GtkListStore and GtkTreeStore have persistent iters, so storing iters is possible. However, using tree row references is definitively the Right Way(tm) to do things, even though it comes with some overhead that might impact performance in case of trees that have a very large number of rows (in that case it might be preferable to write a custom model anyway though). Especially beginners might find it easier to handle and store tree row references than iters, because tree row references are handled by pointer value, which you can easily add to a GList or pointer array, while it is easy to store tree iters in a wrong way.

Usage

Tree iters can easily be converted into tree paths using gtk_tree_model_get_path(), and tree paths can easily be converted into tree iters using gtk_tree_model_get_iter(). Here is an example that shows how to get the iter from the tree path that is passed to us from the tree view in the “row-activated” signal callback. We need the iter here to retrieve data from the store:

void
onTreeViewRowActivated (GtkTreeView *view,
                        GtkTreePath *path,
                        GtkTreeViewColumn *col,
                        gpointer userdata)
{
  GtkTreeModel *model = gtk_tree_view_get_model(view);

  GtkTreeIter iter;
  if (gtk_tree_model_get_iter(model, &iter, path))
    {
      char *name;

      gtk_tree_model_get(model, &iter, COL_NAME, &name, -1);

      g_print ("The row containing the name '%s' has been double-clicked.\n", name);

      g_free(name);
    }
}

Tree row references reveal the current path of a row with gtk_tree_row_reference_get_path(). There is no direct way to get a tree iter from a tree row reference, you have to retrieve the tree row reference’s path first and then convert that into a tree iter.

As tree iters are only valid for a short time, they are usually allocated on the stack, as in the following example (keep in mind that GtkTreeIter is just a structure that contains data fields you do not need to know anything about):

void
traverse_list_store (GtkListStore *liststore)
{
  GtkTreeIter iter;
  gboolean valid;

  g_return_if_fail (liststore != NULL);

  /* Get first row in list store */
  valid = gtk_tree_model_get_iter_first(GTK_TREE_MODEL(liststore), &iter);

  while (valid)
    {
      /* ... do something with that row using the iter ...          */
      /* (Here column 0 of the list store is of type G_TYPE_STRING) */
      gtk_list_store_set(liststore, &iter, 0, "Joe", -1);

      /* Make iter point to the next row in the list store */
      valid = gtk_tree_model_iter_next(GTK_TREE_MODEL(liststore), &iter);
    }
}

The code above asks the model to fill the iter structure to make it point to the first row in the list store. If there is a first row and the list store is not empty, the iter will be set, and gtk_tree_model_get_iter_first() will return TRUE. If there is no first row, it will just return FALSE. If a first row exists, the while loop will be entered and we change some of the first row’s data. Then we ask the model to make the given iter point to the next row, until there are no more rows, which is when gtk_tree_model_iter_next() returns FALSE. Instead of traversing the list store we could also have used gtk_tree_model_foreach().

Adding Rows to a Store

Adding Rows to a List Store

Rows are added to a list store with gtk_list_store_append(). This will insert a new empty row at the end of the list. There are other functions, documented in the GtkListStore API reference, that give you more control about where exactly the new row is inserted, but as they work very similar to gtk_list_store_append() and are fairly straight-forward to use, we will not deal with them here.

Here is a simple example of how to create a list store and add some (empty) rows to it:

GtkListStore *liststore;
GtkTreeIter iter;

liststore = gtk_list_store_new(1, G_TYPE_STRING);

/* Append an empty row to the list store. Iter will point to the new row */
gtk_list_store_append(liststore, &iter);

/* Append an empty row to the list store. Iter will point to the new row */
gtk_list_store_append(liststore, &iter);

/* Append an empty row to the list store. Iter will point to the new row */
gtk_list_store_append(liststore, &iter);

This in itself is not very useful yet of course. We will add data to the rows in the next section.

Adding Rows to a Tree Store

Adding rows to a tree store works similar to adding rows to a list store, only that gtk_tree_store_append() is the function to use and one more argument is required, namely the tree iter to the parent of the row to insert. If you supply NULL instead of providing the tree iter of another row, a new top-level row will be inserted. If you do provide a parent tree iter, the new empty row will be inserted after any already existing children of the parent. Again, there are other ways to insert a row into the tree store and they are documented in the GtkTreeStore API reference manual. Another short example:

GtkListStore *treestore;
GtkTreeIter iter, child;

treestore = gtk_tree_store_new(1, G_TYPE_STRING);

/* Append an empty top-level row to the tree store.
 *  Iter will point to the new row */
gtk_tree_store_append(treestore, &iter, NULL);

/* Append another empty top-level row to the tree store.
 *  Iter will point to the new row */
gtk_tree_store_append(treestore, &iter, NULL);

/* Append a child to the row we just added.
 *  Child will point to the new row */
gtk_tree_store_append(treestore, &child, &iter);

/* Get the first row, and add a child to it as well (could have been done
 *  right away earlier of course, this is just for demonstration purposes) */
if (gtk_tree_model_get_iter_first(GTK_TREE_MODEL(treestore), &iter))
  {
    /* Child will point to new row */
    gtk_tree_store_append(treestore, &child, &iter);
  }
else
  {
    g_error("Oops, we should have a first row in the tree store!\n");
  }

Speed Issues when Adding a Lot of Rows

A common scenario is that a model needs to be filled with a lot of rows at some point, either at start-up, or when some file is opened. An equally common scenario is that this takes an awfully long time even on powerful machines once the model contains more than a couple of thousand rows, with an exponentially decreasing rate of insertion. As already pointed out above, writing a custom model might be the best thing to do in this case. Nevertheless, there are some things you can do to work around this problem and speed things up a bit even with the stock GTK models:

Firstly, you should detach your list store or tree store from the tree view before doing your mass insertions, then do your insertions, and only connect your store to the tree view again when you are done with your insertions. Like this:

model = gtk_tree_view_get_model(GTK_TREE_VIEW(view));

g_object_ref(model); /* Make sure the model stays with us after the tree view unrefs it */

gtk_tree_view_set_model(GTK_TREE_VIEW(view), NULL); /* Detach model from view */

// ... insert a couple of thousand rows ...

gtk_tree_view_set_model(GTK_TREE_VIEW(view), model); /* Re-attach model to view */

g_object_unref(model);

Secondly, you should make sure that sorting is disabled while you are doing your mass insertions, otherwise your store might be resorted after each and every single row insertion, which is going to be everything but fast.

Thirdly, you should not keep around a lot of tree row references if you have so many rows, because with each insertion (or removal) every single tree row reference will check whether its path needs to be updated or not.

Manipulating Row Data

Adding empty rows to a data store is not terribly exciting, so let’s see how we can add or change data in the store.

gtk_list_store_set() and gtk_tree_store_set() are used to manipulate a given row’s data. There is also gtk_list_store_set_value() and gtk_tree_store_set_value(), but those should only be used by people familiar with GLib’s GValue system.

Both gtk_list_store_set() and gtk_tree_store_set() take a variable number of arguments, and must be terminated with a -1 argument. The first two arguments are a pointer to the model, and the iter pointing to the row whose data we want to change. They are followed by a variable number of (column, data) argument pairs, terminated by a -1. The column refers to the model column number and is usually an enum value (to make the code more readable and to make changes easier). The data should be of the same data type as the model column.

Here is an example where we create a store that stores two strings and one integer for each row:

enum
{
  COL_FIRST_NAME = 0,
  COL_LAST_NAME,
  COL_YEAR_BORN,
  NUM_COLS
};

GtkListStore *liststore;
GtkTreeIter   iter;

liststore = gtk_list_store_new(NUM_COLS, G_TYPE_STRING, G_TYPE_STRING, G_TYPE_UINT);

/* Append an empty row to the list store. Iter will point to the new row */
gtk_list_store_append(liststore, &iter);

/* Fill fields with some data */
gtk_list_store_set (liststore, &iter,
                    COL_FIRST_NAME, "Joe",
                    COL_LAST_NAME, "Average",
                    COL_YEAR_BORN, (guint) 1970,
                    -1);

You do not need to worry about allocating and freeing memory for the data to store. The model (or more precisely: the GLib/GObject GType and GValue system) will take care of that for you. If you store a string, for example, the model will make a copy of the string and store that. If you then set the field to a new string later on, the model will automatically free the old string and again make a copy of the new string and store the copy. This applies to almost all types, be it G_TYPE_STRING or GDK_TYPE_PIXBUF.

The exception to note is G_TYPE_POINTER. If you allocate a chunk of data or a complex structure and store it in a G_TYPE_POINTER field, only the pointer value is stored. The model does not know anything about the size or content of the data your pointer refers to, so it could not even make a copy if it wanted to, so you need to allocate and free the memory yourself in this case. However, if you do not want to do that yourself and want the model to take care of your custom data for you, then you need to register your own type and derive it from one of the GLib fundamental types (usually G_TYPE_BOXED). See the GObject reference manual for details. Making a copy of data involves memory allocation and other overhead of course, so one should consider the performance implications of using a custom GLib type over a G_TYPE_POINTER carefully before taking that approach. Again, a custom model might be the better alternative, depending on the overall amount of data to be stored (and retrieved).

Retrieving Row Data

Storing data is not very useful if it cannot be retrieved again. This is done using gtk_tree_model_get(), which takes similar arguments as gtk_list_store_set() or gtk_tree_store_setdo()“, only that it takes (column, pointer) arguments. The pointer must point to a variable that is of the same type as the data stored in that particular model column.

Here is the previous example extended to traverse the list store and print out the data stored. As an extra, we use gtk_tree_model_foreach() to traverse the store and retrieve the row number from the GtkTreePath passed to us in the foreach callback function:

#include <gtk/gtk.h>

enum
{
  COL_FIRST_NAME = 0,
  COL_LAST_NAME,
  COL_YEAR_BORN,
  NUM_COLS
};

gboolean
foreach_func (GtkTreeModel *model,
              GtkTreePath  *path,
              GtkTreeIter  *iter,
              gpointer      user_data)
{
  char *first_name, *last_name, *tree_path_str;
  guint year_of_birth;

  /* Note: here we use 'iter' and not '&iter', because we did not allocate
   *  the iter on the stack and are already getting the pointer to a tree iter
   */
  gtk_tree_model_get (model, iter,
                      COL_FIRST_NAME, &first_name,
                      COL_LAST_NAME, &last_name,
                      COL_YEAR_BORN, &year_of_birth,
                      -1);

  tree_path_str = gtk_tree_path_to_string(path);

  g_print ("Row %s: %s %s, born %u\n", tree_path_str,
           first_name, last_name, year_of_birth);

  g_free(tree_path_str);

  g_free(first_name); /* gtk_tree_model_get made copies of       */
  g_free(last_name);  /* the strings for us when retrieving them */

  return FALSE; /* do not stop walking the store, call us with next row */
}

void
create_and_fill_and_dump_store (void)
{
  GtkListStore *liststore;
  GtkTreeIter iter;

  liststore = gtk_list_store_new(NUM_COLS, G_TYPE_STRING, G_TYPE_STRING, G_TYPE_UINT);

  /* Append an empty row to the list store. Iter will point to the new row */
  gtk_list_store_append(liststore, &iter);

  /* Fill fields with some data */
  gtk_list_store_set (liststore, &iter,
                      COL_FIRST_NAME, "Joe",
                      COL_LAST_NAME, "Average",
                      COL_YEAR_BORN, (guint) 1970,
                      -1);

  /* Append another row, and fill in some data */
  gtk_list_store_append(liststore, &iter);

  gtk_list_store_set (liststore, &iter,
                      COL_FIRST_NAME, "Jane",
                      COL_LAST_NAME, "Common",
                      COL_YEAR_BORN, (guint) 1967,
                      -1);

  /* Append yet another row, and fill it */
  gtk_list_store_append(liststore, &iter);

  gtk_list_store_set (liststore, &iter,
                      COL_FIRST_NAME, "Yo",
                      COL_LAST_NAME, "Da",
                      COL_YEAR_BORN, (guint) 1873,
                      -1);

  /* Now traverse the list */
  gtk_tree_model_foreach(GTK_TREE_MODEL(liststore), foreach_func, NULL);
}

int
main (int argc, char **argv)
{
  gtk_init(&argc, &argv);

  create_and_fill_and_dump_store();

  return 0;
}

Note that when a new row is created, all fields of a row are set to a default “zero” value appropriate for the data type in question. A field of type G_TYPE_INT will automatically contain the value 0 until it is set to a different value, and strings and all kind of pointer types will be NULL until set to something else. Those are valid contents for the model, and if you are not sure that row contents have been set to something, you need to be prepared to handle NULL pointers and the like in your code.

Run the above program with an additional empty row and look at the output to see this in effect.

Freeing Retrieved Row Data

Unless you are dealing with a model column of type G_TYPE_POINTER, gtk_tree_model_get() will always make copies of the data retrieved.

In the case of strings, this means that you need to g_free() the string returned when you don’t need it any longer, as in the example above.

If you retrieve a GObject such as a GdkPixbuf from the store, gtk_tree_model_get() will automatically acquire a reference to it, so you need to call g_object_unref() on the retrieved object once you are done with it, to release the reference:

GdkPixbuf *pixbuf;

gtk_tree_model_get (model, &iter, 
                    COL_PICTURE, &pixbuf, 
                    NULL);

if (pixbuf != NULL)
  {
    do_something_with_pixbuf (pixbuf);
    g_object_unref (pixbuf);
  }

Similarly, GBoxed-derived types retrieved from a model need to be freed with g_boxed_free() when done with them (don’t worry if you have never heard of GBoxed).

If the model column is of type G_TYPE_POINTER, gtk_tree_model_get() will simply copy the pointer value, but not the data (even if if it wanted to, it couldn’t copy the data, because it would not know how to copy it or what to copy exactly). If you store pointers to objects or strings in a pointer column (which you should not do unless you really know what you are doing and why you are doing it), you do not need to unref or free the returned values as described above, because gtk_tree_model_get() would not know what kind of data they are and therefore won’t ref or copy them on retrieval.

Removing Rows

Rows can easily be removed with gtk_list_store_remove() and gtk_tree_store_remove(). The removed row will automatically be removed from the tree view as well, and all data stored will automatically be freed, with the exception of G_TYPE_POINTER columns (see above).

Removing a single row is fairly straight forward: you need to get the iter that identifies the row you want to remove, and then use one of the above functions. Here is a simple example that removes a row when you double-click on it (bad from a user interface point of view, but then it is just an example):

static void
onRowActivated (GtkTreeView        *view,
                GtkTreePath        *path,
                GtkTreeViewColumn  *col,
                gpointer            user_data)
{
  GtkTreeModel *model;
  GtkTreeIter   iter;

  g_print ("Row has been double-clicked. Removing row.\n");

  model = gtk_tree_view_get_model(view);

  if (!gtk_tree_model_get_iter(model, &iter, path))
    return; /* path describes a non-existing row - should not happen */

  gtk_list_store_remove(GTK_LIST_STORE(model), &iter);
}

void
create_treeview (void)
{
  // ...

  g_signal_connect(treeview, "row-activated", G_CALLBACK(onRowActivated), NULL);

  // ...
}

If you want to remove the n-th row from a list (or the n-th child of a tree node), you have two approaches: either you first create a GtkTreePath that describes that row and then turn it into an iter and remove it; or you take the iter of the parent node and use gtk_tree_model_iter_nth_child() (which will also work for list stores if you use NULL as the parent iter. Of course you could also start with the iter of the first top-level row, and then step-by-step move it to the row you want, although that seems a rather awkward way of doing it.

The following code snippet will remove the n-th row of a list if it exists:

gboolean
list_store_remove_nth_row (GtkListStore *store, gint n)
{
  GtkTreeIter  iter;

  g_return_val_if_fail (GTK_IS_LIST_STORE(store), FALSE);

  /* NULL means the parent is the virtual root node, so the
   * n-th top-level element is returned in iter, which is
   * the n-th row in a list store (as a list store only has
   * top-level elements, and no children)
   */
  if (gtk_tree_model_iter_nth_child(GTK_TREE_MODEL(store), &iter, NULL, n))
    {
      gtk_list_store_remove(store, &iter);
      return TRUE;
    }

  return FALSE;
}

Removing Multiple Rows

Removing multiple rows at once can be a bit tricky at times, and requires some thought on how to do this best. For example, it is not possible to traverse a store with gtk_tree_model_foreach(), check in the callback function whether the given row should be removed and then just remove it by calling one of the stores’ remove functions. This will not work, because the model is changed from within the foreach loop, which might suddenly invalidate formerly valid tree iters in the foreach function, and thus lead to unpredictable results.

You could traverse the store in a while loop of course, and call gtk_list_store_remove() or gtk_tree_store_remove() whenever you want to remove a row, and then just continue if the remove functions returns TRUE (meaning that the iter is still valid and now points to the row after the row that was removed).

Here is an example for an alternative approach to removing multiple rows in one go (here we want to remove all rows from the store that contain persons that have been born after 1980, but it could just as well be all selected rows or some other criterion):

gboolean
foreach_func (GtkTreeModel *model,
              GtkTreePath  *path,
              GtkTreeIter  *iter,
              GList       **rowref_list)
{
  guint year_of_birth;

  g_assert (rowref_list != NULL);

  gtk_tree_model_get (model, iter, COL_YEAR_BORN, &year_of_birth, -1);

  if (year_of_birth > 1980)
    {
      GtkTreeRowReference  *rowref;

      rowref = gtk_tree_row_reference_new(model, path);

      *rowref_list = g_list_append(*rowref_list, rowref);
    }

  return FALSE; /* do not stop walking the store, call us with next row */
}

void
remove_people_born_after_1980 (void)
{
  GList *rr_list = NULL;    /* list of GtkTreeRowReferences to remove */
  GList *node;

  gtk_tree_model_foreach(GTK_TREE_MODEL(store),
                         (GtkTreeModelForeachFunc) foreach_func,
                         &rr_list);

  for (node = rr_list;  node != NULL;  node = node->next)
    {
      GtkTreePath *path;

      path = gtk_tree_row_reference_get_path((GtkTreeRowReference*)node->data);

      if (path)
        {
          GtkTreeIter iter;

          if (gtk_tree_model_get_iter(GTK_TREE_MODEL(store), &iter, path))
            gtk_list_store_remove(store, &iter);

          gtk_tree_path_free(path);
        }
    }

  g_list_free_full(rr_list, (GDestroyNotify)gtk_tree_row_reference_free);
}

gtk_list_store_clear() and gtk_tree_store_clear() come in handy if you want to remove all rows.

Storing GObjects (Pixbufs etc.)

A special case are GObject types, like GDK_TYPE_PIXBUF, that get stored in a list or tree store. The store will not make a copy of the object, rather it will increase the object’s refcount. The store will then unref the object again if it is no longer needed (ie. a new object is stored in the old object’s place, the current value is replaced by NULL, the row is removed, or the store is destroyed).

From a developer perspective, this means that you need to g_object_unref() an object that you have just added to the store if you want the store to automatically dispose of it when no longer needed. This is because on object creation, the object has an initial refcount of 1, which is “your” refcount, and the object will only be destroyed when it reaches a refcount of 0. Here is the life cycle of a pixbuf:

GtkListStore *list_store;
GtkTreeIter iter;
GdkPixbuf *pixbuf;
GError *error = NULL;

list_store = gtk_list_store_new (2, GDK_TYPE_PIXBUF, G_TYPE_STRING);

pixbuf = gdk_pixbuf_new_from_file("icon.png", &error);

/* pixbuf has a refcount of 1 after creation */

if (error)
  {
    g_critical ("Could not load pixbuf: %s\n", error->message);
    g_error_free(error);
    return;
  }

gtk_list_store_append(list_store, &iter);

gtk_list_store_set(list_store, &iter, 0, pixbuf, 1, "foo", -1);

/* pixbuf has a refcount of 2 now, as the list store has added its own reference */

g_object_unref(pixbuf);

/* pixbuf has a refcount of 1 now that we have released our initial reference */

/* we don't want an icon in that row any longer */
gtk_list_store_set(list_store, &iter, 0, NULL, -1);

/* pixbuf has automatically been destroyed after its refcount has reached 0.
 *  The list store called g_object_unref() on the pixbuf when it replaced
 *  the object in the store with a new value (NULL). */

Having learned how to add, manipulate, and retrieve data from a store, the next step is to get that data displayed in a GtkTreeView widget.

Creating a Tree View

In order to display data in a tree view widget, we need to create one first, and we need to instruct it where to get the data to display from.

A new tree view is created with:

GtkWidget *view;

view = gtk_tree_view_new();

Connecting Tree View and Model

Before we proceed to the next section where we display data on the screen, we need connect our data store to the tree view, so it knows where to get the data to display from. This is achieved with gtk_tree_view_set_model(), which will by itself do very little. However, it is a prerequisite for what we do in the following sections. gtk_tree_view_new_with_model() is a convenience function for the previous two.

gtk_tree_view_get_model() will return the model that is currently attached to a given tree view, which is particularly useful in callbacks where you only get passed the tree view widget (after all, we do not want to go down the road of global variables, which will inevitably lead to the Dark Side, do we?).

Reference counting

Tree models like GtkListStore and GtkTreeStore are GObjects and have a reference count of 1 after creation. The tree view will add its own reference to the model when you add the model with gtk_tree_view_set_model(), and will unref it again when you replace the model with another model, unset the model by passing NULL as a model, or when the tree view is destroyed.

Reference counting’ means that an object has a counter that can be increased or decreased (ref-ed and unref-ed). If the counter is unref-ed to 0, the object is automatically destroyed. This is useful, because other objects or application programmers only have to think about whether they themselves are still using that object or not, without knowing anything about others also using it. The object is simply automatically destroyed when no one is using it any more.

This means that you need to take care of “your” reference yourself, otherwise the model will not be destroyed properly when you disconnect it from the tree view, and its memory will not be freed (which does not matter much if the same model is connected to the tree view from application start to end). If you plan to use the same model for a tree view for the whole duration of the application, you can get rid of “your” reference right after you have connected the model to the view - then the model will be destroyed automatically when the tree view is destroyed (which will be automatically destroyed when the window it is in is destroyed):

GtkListStore *liststore;
GtkWidget    *view;

view = gtk_tree_view_new();

liststore = gtk_list_store_new(1, G_TYPE_STRING);

gtk_tree_view_set_model(GTK_TREE_VIEW(view), GTK_TREE_MODEL(liststore));

g_object_unref(liststore);

/* Now the model will be destroyed when the tree view is destroyed */

Tree View Look and Feel

There are a couple of ways to influence the look and feel of the tree view. You can hide or show column headers with gtk_tree_view_set_headers_visible(), and set them clickable or not with gtk_tree_view_set_headers_clickable() (which will be done automatically for you if you enable sorting).

gtk_tree_view_set_rules_hint() will enable or disable rules in the tree view. As the function name implies, this setting is only a hint; in the end it depends on the active GTK theme engine if the tree view shows ruled lines or not. Users seem to have strong feelings about rules in tree views, so it is probably a good idea to provide an option somewhere to disable rule hinting if you set it on tree views (but then, people also seem to have strong feelings about options abundance and ‘sensible’ default options, so whatever you do will probably upset someone at some point).

The expander column can be set with gtk_tree_view_set_expander_column(). This is the column where child elements are indented with respect to their parents, and where rows with children have an ‘expander’ arrow with which a node’s children can be collapsed (hidden) or expanded (shown). By default, this is the first column.

Mapping Data to the Screen: GtkTreeViewColumn and GtkCellRenderer

As outlined above, tree view columns represent the visible columns on the screen that have a column header with a column name and can be resized or sorted. A tree view is made up of tree view columns, and you need at least one tree view column in order to display something in the tree view. Tree view columns, however, do not display anything by themselves, this is done by specialised GtkCellRenderer objects. Cell renderers are packed into tree view columns much like widgets are packed into GtkBoxes.

Here is a diagram (courtesy of Owen Taylor) that pictures the relationship between tree view columns and cell renderers:

In the above diagram, both ‘Country’ and ‘Representative’ are tree view columns, where the ‘Country’ and ‘Representative’ labels are the column headers. The ‘Country’ column contains two cell renderers, one to display the flag icons, and one to display the country name. The ‘Representative’ column only contains one cell renderer to display the representative’s name.

Cell Renderers

Cell renderers are objects that are responsible for the actual rendering of data within a GtkTreeViewColumn. They are basically just GObjects (ie. not widgets) that have certain properties, and those properties determine how a single cell is drawn.

In order to draw cells in different rows with different content, a cell renderer’s properties need to be set accordingly for each single row/cell to render. This is done either via attributes or cell data functions (see below). If you set up attributes, you tell Gtk which model column contains the data from which a property should be set before rendering a certain row. Then the properties of a cell renderer are set automatically according to the data in the model before each row is rendered. Alternatively, you can set up cell data functions, which are called for each row to be rendererd, so that you can manually set the properties of the cell renderer before it is rendered. Both approaches can be used at the same time as well. Lastly, you can set a cell renderer property when you create the cell renderer. That way it will be used for all rows/cells to be rendered (unless it is changed later of course).

Different cell renderers exist for different purposes:

  • GtkCellRendererText renders strings or numbers or boolean values as text (“Joe”, “99.32”, “true”)
  • GtkCellRendererPixbuf is used to display images; either user-defined images, or one of the stock icons that come with GTK.
  • GtkCellRendererToggle displays a boolean value in form of a check box or as a radio button.
  • GtkCellEditable is a special cell that implements editable cells (ie. GtkEntry or GtkSpinbutton in a treeview). This is not a cell renderer! If you want to have editable text cells, use GtkCellRendererText and make sure the “editable” property is set. GtkCellEditable is only used by implementations of editable cells and widgets that can be inside of editable cells. You are unlikely to ever need it.

Contrary to what one may think, a cell renderer does not render just one single cell, but is responsible for rendering part or whole of a tree view column for each single row. It basically starts in the first row and renders its part of the column there. Then it proceeds to the next row and renders its part of the column there again. And so on.

How does a cell renderer know what to render? A cell renderer object has certain ‘properties’ that are documented in the API reference (just like most other objects, and widgets). These properties determine what the cell renderer is going to render and how it is going to be rendered. Whenever the cell renderer is called upon to render a certain cell, it looks at its properties and renders the cell accordingly. This means that whenever you set a property or change a property of the cell renderer, this will affect all rows that are rendered after the change, until you change the property again.

Here is a diagram (courtesy of Owen Taylor) that tries to show what is going on when rows are rendered:

The above diagram shows the process when attributes are used. In the example, a text cell renderer’s “text” property has been linked to the first model column. The “text” property contains the string to be rendered. The “foreground” property, which contains the colour of the text to be shown, has been linked to the second model column. Finally, the “strikethrough” property, which determines whether the text should be with a horizontal line that strikes through the text, has been connected to the third model column (of type G_TYPE_BOOLEAN).

With this setup, the cell renderer’s properties are ‘loaded’ from the model before each cell is rendered.

Here is a silly and utterly useless little example that demonstrates this behaviour, and introduces some of the most commonly used properties of GtkCellRendererText:

#include <gtk/gtk.h>

enum
{
  COL_FIRST_NAME = 0,
  COL_LAST_NAME,
  NUM_COLS
} ;

static GtkTreeModel *
create_and_fill_model (void)
{
  GtkTreeStore  *treestore;
  GtkTreeIter    toplevel, child;

  treestore = gtk_tree_store_new(NUM_COLS, G_TYPE_STRING, G_TYPE_STRING);

  /* Append a top level row and leave it empty */
  gtk_tree_store_append(treestore, &toplevel, NULL);

  /* Append a second top level row, and fill it with some data */
  gtk_tree_store_append(treestore, &toplevel, NULL);
  gtk_tree_store_set(treestore, &toplevel,
                     COL_FIRST_NAME, "Joe",
                     COL_LAST_NAME, "Average",
                     -1);

  /* Append a child to the second top level row, and fill in some data */
  gtk_tree_store_append(treestore, &child, &toplevel);
  gtk_tree_store_set(treestore, &child,
                     COL_FIRST_NAME, "Jane",
                     COL_LAST_NAME, "Average",
                     -1);

  return GTK_TREE_MODEL(treestore);
}

static GtkWidget *
create_view_and_model (void)
{
  GtkTreeViewColumn   *col;
  GtkCellRenderer     *renderer;
  GtkWidget           *view;
  GtkTreeModel        *model;

  view = gtk_tree_view_new();

  /* --- Column #1 --- */

  col = gtk_tree_view_column_new();

  gtk_tree_view_column_set_title(col, "First Name");

  /* pack tree view column into tree view */
  gtk_tree_view_append_column(GTK_TREE_VIEW(view), col);

  renderer = gtk_cell_renderer_text_new();

  /* pack cell renderer into tree view column */
  gtk_tree_view_column_pack_start(col, renderer, TRUE);

  /* set 'text' property of the cell renderer */
  g_object_set(renderer, "text", "Boooo!", NULL);


  /* --- Column #2 --- */

  col = gtk_tree_view_column_new();

  gtk_tree_view_column_set_title(col, "Last Name");

  /* pack tree view column into tree view */
  gtk_tree_view_append_column(GTK_TREE_VIEW(view), col);

  renderer = gtk_cell_renderer_text_new();

  /* pack cell renderer into tree view column */
  gtk_tree_view_column_pack_start(col, renderer, TRUE);

  /* set 'cell-background' property of the cell renderer */
  g_object_set(renderer,
               "cell-background", "Orange",
               "cell-background-set", TRUE,
               NULL);

  model = create_and_fill_model();

  gtk_tree_view_set_model(GTK_TREE_VIEW(view), model);

  g_object_unref(model); /* destroy model automatically with view */

  gtk_tree_selection_set_mode(gtk_tree_view_get_selection(GTK_TREE_VIEW(view)),
                              GTK_SELECTION_NONE);

  return view;
}


int
main (int argc, char **argv)
{
  GtkWidget *window;
  GtkWidget *view;

  gtk_init(&argc, &argv);

  window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
  g_signal_connect(window, "delete_event", gtk_main_quit, NULL); /* dirty */

  view = create_view_and_model();

  gtk_container_add(GTK_CONTAINER(window), view);

  gtk_widget_show_all(window);

  gtk_main();

  return 0;
}

The above code should produce something looking like this:

It looks like the tree view display is partly correct and partly incomplete. On the one hand the tree view renders the correct number of rows (note how there is no orange on the right after row 3), and it displays the hierarchy correctly (on the left), but it does not display any of the data that we have stored in the model. This is because we have made no connection between what the cell renderers should render and the data in the model. We have simply set some cell renderer properties on start-up, and the cell renderers adhere to those set properties meticulously.

There are two different ways to connect cell renderers to data in the model: attributes and cell data functions.

Attributes

An attribute is a connection between a cell renderer property and a field/column in the model. Whenever a cell is to be rendered, a cell renderer property will be set to the values of the specified model column of the row that is to be rendered. It is very important that the column’s data type is the same type that a property takes according to the API reference manual. Here is some code to look at:

col = gtk_tree_view_column_new();

renderer = gtk_cell_renderer_text_new();

gtk_tree_view_column_pack_start(col, renderer, TRUE);

gtk_tree_view_column_add_attribute(col, renderer, "text", COL_FIRST_NAME);

This means that the text cell renderer property “text” will be set to the string in model column COL_FIRST_NAME of each row to be drawn. It is important to internalise the difference between gtk_tree_view_column_add_attribute() and g_object_set(): g_object_set() sets a property to a certain value, while gtk_tree_view_column_add_attribute() sets a property to whatever is in the specified model column at the time of rendering.

Again, when setting attributes it is very important that the data type stored in a model column is the same as the data type that a property requires as argument. Check the API reference manual to see the data type that is required for each property. When reading through the example a bit further above, you might have noticed that we set the “cell-background” property of a GtkCellRendererText, even though the API documentation does not list such a property. We can do this, because GtkCellRendererText is derived from GtkCellRenderer, which does in fact have such a property. Derived classes inherit the properties of their parents. This is the same as with widgets that you can cast into one of their ancestor classes. The API reference has an object hierarchy that shows you which classes a widget or some other object is derived from.

There are two more noteworthy things about GtkCellRenderer properties: one is that sometimes there are different properties which do the same, but take different arguments, such as the “foreground” and “foreground-gdk” properties of GtkCellRendererText (which specify the text colour). The “foreground” property take a colour in string form, such as “Orange” or “CornflowerBlue”, whereas “foreground-gdk” takes a GdkColor argument. It is up to you to decide which one to use - the effect will be the same. The other thing worth mentioning is that most properties have a “foo-set” property taking a boolean value as argument, such as “foreground-set”. This is useful when you want to have a certain setting have an effect or not. If you set the “foreground” property, but set “foreground-set” to FALSE, then your foreground color setting will be disregarded. This is useful in cell data functions (see below), or, for example, if you want set the foreground colour to a certain value at start-up, but only want this to be in effect in some columns, but not in others (in which case you could just connect the “foreground-set” property to a model column of type G_TYPE_BOOLEAN with gtk_tree_view_column_add_attribute().

Setting column attributes is the most straight-forward way to get your model data to be displayed. This is usually used whenever you want the data in the model to be displayed exactly as it is in the model.

Another way to get your model data displayed on the screen is to set up cell data functions.

Cell Data Functions

A cell data function is a function that is called for a specific cell renderer for each single row before that row is rendered. It gives you maximum control over what exactly is going to be rendered, as you can set the cell renderer’s properties just like you want to have them. Remember not only to set a property if you want it to be active, but also to unset a property if it should not be active (and it might have been set in the previous row).

Cell data functions are often used if you want more fine-grained control over what is to be displayed, or if the standard way to display something is not quite like you want it to be. A case in point are floating point numbers. If you want floating point numbers to be displayed in a certain way, say with only one digit after the colon/comma, then you need to use a cell data function. Use gtk_tree_view_column_set_cell_data_func() to set up a cell data function for a particular cell renderer. Here is an example:

enum
{
  COLUMN_NAME = 0,
  COLUMN_AGE_FLOAT,
  NUM_COLS
};

// ...

void
age_cell_data_function (GtkTreeViewColumn *col,
                        GtkCellRenderer   *renderer,
                        GtkTreeModel      *model,
                        GtkTreeIter       *iter,
                        gpointer           user_data)
{
  float  age;
  char buf[20];

  gtk_tree_model_get(model, iter, COLUMN_AGE_FLOAT, &age, -1);

  g_snprintf(buf, sizeof(buf), "%.1f", age);

  g_object_set(renderer, "text", buf, NULL);
}

// ...

liststore = gtk_list_store_new(NUM_COLS, G_TYPE_STRING, G_TYPE_FLOAT);

col = gtk_tree_view_column_new();

cell = gtk_cell_renderer_text_new();

gtk_tree_view_column_pack_start(col, cell, TRUE);

gtk_tree_view_column_set_cell_data_func(col, cell, age_cell_data_func, NULL, NULL);

for each row to be rendered by this particular cell renderer, the cell data function is going to be called, which then retrieves the float from the model, and turns it into a string where the float has only one digit after the colon/comma, and renders that with the text cell renderer.

This is only a simple example, you can make cell data functions a lot more complicated if you want to. As always, there is a trade-off to keep in mind though. Your cell data function is going to be called every single time a cell in that (renderer) column is going to be rendered. Go and check how often this function is called in your program if you ever use one. If you do time-consuming operations within a cell data function, things are not going to be fast, especially if you have a lot of rows. The alternative in this case would have been to make an additional column COLUMN_AGE_FLOAT_STRING of type G_TYPE_STRING, and to set the float in string form whenever you set the float itself in a row, and then hook up the string column to a text cell renderer using attributes. This way the float to string conversion would only need to be done once. This is a cpu cycles / memory trade-off, and it depends on your particular case which one is more suitable. Things you should probably not do is to convert long strings into UTF8 format in a cell data function, for example.

You might notice that your cell data function is called at times even for rows that are not visible at the moment. This is because the tree view needs to know its total height, and in order to calculate this it needs to know the height of each and every single row, and it can only know that by having it measured, which is going to be slow when you have a lot of rows with different heights (if your rows all have the same height, there should not be any visible delay though).

GtkCellRendererText and Integer, Boolean and Float Types

It has been said before that, when using attributes to connect data from the model to a cell renderer property, the data in the model column specified in gtk_tree_view_column_add_attribute() must always be of the same type as the data type that the property requires.

This is usually true, but there is an exception: if you use gtk_tree_view_column_add_attribute() to connect a text cell renderer’s “text” property to a model column, the model column does not need to be of G_TYPE_STRING, it can also be one of most other fundamental GLib types, e.g. G_TYPE_BOOLEAN, G_TYPE_INT, G_TYPE_UINT, G_TYPE_LONG, G_TYPE_ULONG, G_TYPE_INT64, G_TYPE_UINT64, G_TYPE_FLOAT, or G_TYPE_DOUBLE. The text cell renderer will automatically display the values of these types correctly in the tree view. For example:

enum
{
  COL_NAME = 0,
  COL_YEAR_BORN,
  NUM_COLS
};

liststore = gtk_list_store_new(NUM_COLS, G_TYPE_STRING, G_TYPE_UINT);

// ...

cell = gtk_cell_renderer_text_new();
col = gtk_tree_view_column_new();
gtk_tree_view_column_add_attribute(col, cell, "text", COL_YEAR_BORN);

Even though the “text” property would require a string value, we use a model column of an integer type when setting attributes. The integer will then automatically be converted into a string before the cell renderer property is set.

If you are using a floating point type, ie. G_TYPE_FLOAT or G_TYPE_DOUBLE, there is no way to tell the text cell renderer how many digits after the floating point (or comma) should be rendered. If you only want a certain amount of digits after the point/comma, you will need to use a cell data function.

GtkCellRendererText, UTF8, and pango markup

All text used in GTK widgets needs to be in UTF8 encoding, and GtkCellRendererText is no exception. Text in plain ASCII is automatically valid UTF8, but as soon as you have special characters that do not exist in plain ASCII (usually characters that are not used in the English language alphabet), they need to be in UTF8 encoding. There are many different character encodings that all specify different ways to tell the computer which character is meant. GTK uses UTF8, and whenever you have text that is in a different encoding, you need to convert it to UTF8 encoding first, using one of the GLib g_convert*() family of functions. If you only use text input from other GTK widgets, you are on the safe side, as they will return all text in UTF8 as well.

However, if you use ‘external’ sources of text input, then you must convert that text from the text’s encoding (or the user’s locale) to UTF8, or it will not be rendered correctly (either not at all, or it will be cut off after the first invalid character). Filenames are especially hard, because there is no indication whatsoever what character encoding a filename is in (it might have been created when the user was using a different locale, so filename encoding is basically unreliable and broken). You may want to convert to UTF8 with fallback characters in that case. You can check whether a string is valid UTF8 with g_utf8_validate(). You should, in this author’s opinion at least, put these checks into your code at crucial places wherever it is not affecting performance, especially if you are an English-speaking programmer that has little experience with non-English locales. It will make it easier for others and yourself to spot problems with non-English locales later on.

In addition to the “text” property, GtkCellRendererText also has a “markup” property that takes text with Pango markup as input. Pango markup allows you to place special tags into a text string that affect the style the text is rendered (see the pango documentation). Basically you can achieve everything you can achieve with the other properties also with Pango markup (only that using properties is more efficient and less messy). Pango markup has one distinct advantage though that you cannot achieve with text cell renderer properties: with Pango markup, you can change the text style in the middle of the text, so you could, for example, render one part of a text string in bold print, and the rest of the text in normal. Here is an example of a string with pango markup:

"You can have text in <b>bold</b> or in a <span color='Orange'>different color</span>"

When using the “markup” property, you need to take into account that the “markup” and “text” properties do not seem to be mutually exclusive (I suppose this could be called a bug). In other words: whenever you set “markup” (and have used the “text” property before), set the “text” property to NULL, and vice versa. Example:

void
foo_cell_data_function ( ... )
{
  // ...

  if (foo->is_important)
    g_object_set(renderer, "markup", "<b>important</b>", "text", NULL, NULL);
  else
    g_object_set(renderer, "markup", NULL, "text", "not important", NULL);

  // ...
}

Another thing to keep in mind when using pango markup text is that you might need to escape text if you construct strings with pango markup on the fly using random input data. For example:

void
foo_cell_data_function ( ... )
{
  char *markuptxt;

  /* This might be problematic if artist_string or title_string
   * contain markup characters/entities:
   */
  markuptxt = g_strdup_printf("<b>%s</b> - <i>%s</i>",
                              artist_string, title_string);
  // ...

  g_object_set(renderer, "markup", markuptxt, "text", NULL, NULL);

  //...

  g_free(markuptxt);
}

The above example will not work if artist_string is “Simon & Garfunkel” for example, because the & character is one of the characters that is special. They need to be escaped, so that pango knows that they do not refer to any pango markup, but are just characters. In this case the string would need to be “Simon & Garfunkel” in order to make sense in between the pango markup in which it is going to be pasted. You can escape a string with g_markup_escape() (and you will need to free the resulting newly-allocated string again with g_free()).

It is possible to combine both pango markup and text cell renderer properties. Both will be ‘added’ together to render the string in question, only that the text cell renderer properties will be applied to the whole string. If you set the “markup” property to normal text without any pango markup, it will render as normal text just as if you had used the “text” property. However, as opposed to the “text” property, special characters in the “markup” property text would still need to be escaped, even if you do not use pango markup in the text.

A Working Example

Here is our example from the very beginning again (with an additional column though), only that the contents of the model are rendered properly on the screen this time. Both attributes and a cell data function are used for demonstration purposes.

#include <gtk/gtk.h>

enum
{
  COL_FIRST_NAME = 0,
  COL_LAST_NAME,
  COL_YEAR_BORN,
  NUM_COLS
} ;

static GtkTreeModel *
create_and_fill_model (void)
{
  GtkTreeStore  *treestore;
  GtkTreeIter    toplevel, child;

  treestore = gtk_tree_store_new(NUM_COLS,
                                 G_TYPE_STRING,
                                 G_TYPE_STRING,
                                 G_TYPE_UINT);

  /* Append a top level row and leave it empty */
  gtk_tree_store_append(treestore, &toplevel, NULL);
  gtk_tree_store_set(treestore, &toplevel,
                     COL_FIRST_NAME, "Maria",
                     COL_LAST_NAME, "Incognito",
                     -1);

  /* Append a second top level row, and fill it with some data */
  gtk_tree_store_append(treestore, &toplevel, NULL);
  gtk_tree_store_set(treestore, &toplevel,
                     COL_FIRST_NAME, "Jane",
                     COL_LAST_NAME, "Average",
                     COL_YEAR_BORN, (guint) 1962,
                     -1);

  /* Append a child to the second top level row, and fill in some data */
  gtk_tree_store_append(treestore, &child, &toplevel);
  gtk_tree_store_set(treestore, &child,
                     COL_FIRST_NAME, "Janinita",
                     COL_LAST_NAME, "Average",
                     COL_YEAR_BORN, (guint) 1985,
                     -1);

  return GTK_TREE_MODEL(treestore);
}

void
age_cell_data_func (GtkTreeViewColumn *col,
                    GtkCellRenderer   *renderer,
                    GtkTreeModel      *model,
                    GtkTreeIter       *iter,
                    gpointer           user_data)
{
  guint  year_born;
  guint  year_now = 2003; /* to save code not relevant for the example */
  gchar  buf[64];

  gtk_tree_model_get(model, iter, COL_YEAR_BORN, &year_born, -1);

  if (year_born <= year_now && year_born > 0)
  {
    guint age = year_now - year_born;

    g_snprintf(buf, sizeof(buf), "%u years old", age);

    g_object_set(renderer, "foreground-set", FALSE, NULL); /* print this normal */
  }
  else
  {
    g_snprintf(buf, sizeof(buf), "age unknown");

    /* make red */
    g_object_set(renderer, "foreground", "Red", "foreground-set", TRUE, NULL);
  }

  g_object_set(renderer, "text", buf, NULL);
}

static GtkWidget *
create_view_and_model (void)
{
  GtkTreeViewColumn   *col;
  GtkCellRenderer     *renderer;
  GtkWidget           *view;
  GtkTreeModel        *model;

  view = gtk_tree_view_new();

  /* --- Column #1 --- */

  col = gtk_tree_view_column_new();

  gtk_tree_view_column_set_title(col, "First Name");

  /* pack tree view column into tree view */
  gtk_tree_view_append_column(GTK_TREE_VIEW(view), col);

  renderer = gtk_cell_renderer_text_new();

  /* pack cell renderer into tree view column */
  gtk_tree_view_column_pack_start(col, renderer, TRUE);

  /* connect 'text' property of the cell renderer to
   *  model column that contains the first name */
  gtk_tree_view_column_add_attribute(col, renderer, "text", COL_FIRST_NAME);


  /* --- Column #2 --- */

  col = gtk_tree_view_column_new();

  gtk_tree_view_column_set_title(col, "Last Name");

  /* pack tree view column into tree view */
  gtk_tree_view_append_column(GTK_TREE_VIEW(view), col);

  renderer = gtk_cell_renderer_text_new();

  /* pack cell renderer into tree view column */
  gtk_tree_view_column_pack_start(col, renderer, TRUE);

  /* connect 'text' property of the cell renderer to
   *  model column that contains the last name */
  gtk_tree_view_column_add_attribute(col, renderer, "text", COL_LAST_NAME);

  /* set 'weight' property of the cell renderer to
   *  bold print (we want all last names in bold) */
  g_object_set(renderer,
               "weight", PANGO_WEIGHT_BOLD,
               "weight-set", TRUE,
               NULL);


  /* --- Column #3 --- */

  col = gtk_tree_view_column_new();

  gtk_tree_view_column_set_title(col, "Age");

  /* pack tree view column into tree view */
  gtk_tree_view_append_column(GTK_TREE_VIEW(view), col);

  renderer = gtk_cell_renderer_text_new();

  /* pack cell renderer into tree view column */
  gtk_tree_view_column_pack_start(col, renderer, TRUE);

  /* connect a cell data function */
  gtk_tree_view_column_set_cell_data_func(col, renderer, age_cell_data_func, NULL, NULL);


  model = create_and_fill_model();

  gtk_tree_view_set_model(GTK_TREE_VIEW(view), model);

  g_object_unref(model); /* destroy model automatically with view */

  gtk_tree_selection_set_mode(gtk_tree_view_get_selection(GTK_TREE_VIEW(view)),
                              GTK_SELECTION_NONE);

  return view;
}


int
main (int argc, char **argv)
{
  GtkWidget *window;
  GtkWidget *view;

  gtk_init(&argc, &argv);

  window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
  g_signal_connect(window, "delete_event", gtk_main_quit, NULL); /* dirty */

  view = create_view_and_model();

  gtk_container_add(GTK_CONTAINER(window), view);

  gtk_widget_show_all(window);

  gtk_main();

  return 0;
}

How to Make a Whole Row Bold or Coloured

This seems to be a frequently asked question, so it is worth mentioning it here. You have the two approaches mentioned above: either you use cell data functions, and check in each whether a particular row should be highlighted in a particular way (bold, coloured, whatever), and then set the renderer properties accordingly (and unset them if you want that row to look normal), or you use attributes. Cell data functions are most likely not the right choice in this case though.

If you only want every second line to have a gray background to make it easier for the user to see which data belongs to which line in wide tree views, then you do not have to bother with the stuff mentioned here. Instead just set the rules hint on the tree view as described in the here, and everything will be done automatically, in colours that conform to the chosen theme even (unless the theme disables rule hints, that is).

Otherwise, the most suitable approach for most cases is that you add two columns to your model, one for the property itself (e.g. a column COL_ROW_COLOR of type G_TYPE_STRING), and one for the boolean flag of the property (e.g. a column COL_ROW_COLOR_SET of type G_TYPE_BOOLEAN). You would then connect these columns with the “foreground” and “foreground-set” properties of each renderer. Now, whenever you set a row’s COL_ROW_COLOR field to a colour, and set that row’s COL_ROW_COLOR_SET field to TRUE, then this column will be rendered in the colour of your choice. If you only want either the default text colour or one special other colour, you could even achieve the same thing with just one extra model column: in this case you could just set all renderer’s “foreground” property to whatever special color you want, and only connect the COL_ROW_COLOR_SET column to all renderer’s “foreground-set” property using attributes. This works similar with any other attribute, only that you need to adjust the data type for the property of course (e.g. “weight” would take a PANGO_TYPE_WEIGHT).

As a general rule, you should not change the text colour or the background colour of a cell unless you have a really good reason for it. To quote Havoc Pennington: “Because colors in GTK represent a theme the user has chosen, you should never set colors purely for aesthetic reasons. If users don’t like GTK gray, they can change it themselves to their favorite shade of orange.”

How to Pack Icons into the Tree View

So far we have only put text in the tree view. While everything you need to know to display icons (in the form of GdkPixbufs) has been introduced in the previous sections, a short example might help to make things clearer. The following code will pack an icon and some text into the same tree view column:

enum
{
  COL_ICON = 0,
  COL_TEXT,
  NUM_COLS
};

GtkListStore *
create_liststore(void)
{
  GtkListStore  *store;
  GtkTreeIter    iter;
  GdkPixbuf     *icon;
  GError        *error = NULL;

  store = gtk_list_store_new(2, GDK_TYPE_PIXBUF, G_TYPE_STRING);

  icon = gdk_pixbuf_new_from_file("icon.png", &error);
  if (error)
  {
    g_warning ("Could not load icon: %s\n", error->message);
    g_error_free(error);
    error = NULL;
  }

  gtk_list_store_append(store, &iter);
  gtk_list_store_set(store, &iter,
                     COL_ICON, icon,
                     COL_TEXT, "example",
                     -1);

  return store;
}

GtkWidget *
create_treeview(void)
{
  GtkTreeModel      *model;
  GtkTreeViewColumn *col;
  GtkCellRenderer   *renderer;
  GtkWidget         *view;

  model = GTK_TREE_MODEL(create_liststore());

  view = gtk_tree_view_new_with_model(model);

  col = gtk_tree_view_column_new();
  gtk_tree_view_column_set_title(col, "Title");

  renderer = gtk_cell_renderer_pixbuf_new();
  gtk_tree_view_column_pack_start(col, renderer, FALSE);
  gtk_tree_view_column_set_attributes(col, renderer,
                                      "pixbuf", COL_ICON,
                                      NULL);

  renderer = gtk_cell_renderer_text_new();
  gtk_tree_view_column_pack_start(col, renderer, TRUE);
  gtk_tree_view_column_set_attributes(col, renderer,
                                      "text", COL_TEXT,
                                      NULL);

  gtk_tree_view_append_column(GTK_TREE_VIEW(view), col);

  gtk_widget_show_all(view);

  return view;
}

Note that the tree view will not resize icons for you, but displays them in their original size. If you want to display stock icons instead of GdkPixbufs loaded from file, you should have a look at the “stock-id” property of GtkCellRendererPixbuf (and your model column should be of type G_TYPE_STRING, as all stock IDs are just strings by which to identify the stock icon).

Selections, Double-Clicks and Context Menus

Handling Selections

One of the most basic features of a list or tree view is that rows can be selected or unselected. Selections are handled using the GtkTreeSelection object of a tree view. Every tree view automatically has a GtkTreeSelection associated with it, and you can get it using gtk_tree_view_get_selection(). Selections are handled completely on the tree view side, which means that the model knows nothing about which rows are selected or not. There is no particular reason why selection handling could not have been implemented with functions that access the tree view widget directly, but for reasons of API cleanliness and code clarity the GTK developers decided to create this special GtkTreeSelection object that then internally deals with the tree view widget. You will never need to create a tree selection object, it will be created for you automatically when you create a new tree view. You only need to use said gtk_tree_view_get_selection() function to get a pointer to the selection object.

There are three ways to deal with tree view selections: either you get a list of the currently selected rows whenever you need it, for example within a context menu function, or you keep track of all select and unselect actions and keep a list of the currently selected rows around for whenever you need them; as a last resort, you can also traverse your list or tree and check each single row for whether it is selected or not (which you need to do if you want all rows that are not selected for example).

Selection Modes

You can use gtk_tree_selection_set_mode() to influence the way that selections are handled. There are four selection modes:

  • GTK_SELECTION_NONE - no items can be selected
  • GTK_SELECTION_SINGLE - no more than one item can be selected
  • GTK_SELECTION_BROWSE - exactly one item is always selected
  • GTK_SELECTION_MULTIPLE - anything between no item and all items can be selected

Getting the Currently Selected Rows

You can access the currently selected rows either by traversing all selected rows using gtk_tree_selection_selected_foreach() or get a GList of tree paths of the selected rows using gtk_tree_selection_get_selected_rows().

If the selection mode you are using is either GTK_SELECTION_SINGLE or GTK_SELECTION_BROWSE, the most convenient way to get the selected row is the function gtk_tree_selection_get_selected(), which will return TRUE and fill in the specified tree iter with the selected row (if a row is selected), and return FALSE otherwise. It is used like this:

GtkTreeSelection *selection;
GtkTreeModel *model;
GtkTreeIter iter;

/* This will only work in single or browse selection mode! */

selection = gtk_tree_view_get_selection(GTK_TREE_VIEW(view));
if (gtk_tree_selection_get_selected(selection, &model, &iter))
  {
    char *name;

    gtk_tree_model_get (model, &iter, COL_NAME, &name, -1);

    g_print ("selected row is: %s\n", name);

    g_free(name);
  }
else
  {
    g_print ("no row selected.\n");
  }

One thing you need to be aware of is that you need to take care when removing rows from the model in a gtk_tree_selection_selected_foreach() callback, or when looping through the list that gtk_tree_selection_get_selected_rows() returns (because it contains paths, and when you remove rows in the middle, then the old paths will point to either a non-existing row, or to another row than the one selected). You have two ways around this problem: one way is to use the solution to removing multiple rows that has been described above, ie. to get tree row references for all selected rows and then remove the rows one by one; the other solution is to sort the list of selected tree paths so that the last rows come first in the list, so that you remove rows from the end of the list or tree. You cannot remove rows from within a foreach callback in any case, that is simply not allowed.

Here is an example of how to use gtk_tree_selection_selected_foreach():

gboolean
view_selected_foreach_func (GtkTreeModel  *model,
                            GtkTreePath   *path,
                            GtkTreeIter   *iter,
                            gpointer       userdata)
{
  char *name;

  gtk_tree_model_get (model, iter, COL_NAME, &name, -1);

  g_print ("%s is selected\n", name);

  g_free(name);
}


void
do_something_with_all_selected_rows (GtkWidget *treeview)
{
  GtkTreeSelection *selection = gtk_tree_view_get_selection(GTK_TREE_VIEW(treeview));

  gtk_tree_selection_selected_foreach(selection, view_selected_foreach_func, NULL);
}


void
create_view (void)
{
  GtkWidget *view;
  GtkTreeSelection *selection;

  // ...

  view = gtk_tree_view_new();

  // ...

  selection = gtk_tree_view_get_selection(GTK_TREE_VIEW(view));

  gtk_tree_selection_set_mode(selection, GTK_SELECTION_MULTIPLE);

  // ...
}

Using Selection Functions

You can set up a custom selection function with gtk_tree_selection_set_select_function(). This function will then be called every time a row is going to be selected or unselected (meaning: it will be called before the selection status of that row is changed). Selection functions are commonly used for the following things:

  1. … to keep track of the currently selected items (then you maintain a list of selected items yourself). In this case, note again that your selection function is called before the row’s selection status is changed. In other words: if the row is going to be selected, then the boolean path_currently_selected variable that is passed to the selection function is still FALSE. Also note that the selection function might not always be called when a row is removed, so you either have to unselect a row before you remove it to make sure your selection function is called and removes the row from your list, or check the validity of a row when you process the selection list you keep. You should not store tree paths in your self-maintained list of of selected rows, because whenever rows are added or removed or the model is resorted the paths might point to other rows. Use tree row references or other unique means of identifying a row instead.
  2. … to tell GTK whether it is allowed to select or unselect that specific row (you should make sure though that it is otherwise obvious to a user whether a row can be selected or not, otherwise the user will be confused if she just cannot select or unselect a row). This is done by returning TRUE or FALSE in the selection function.
  3. … to take additional action whenever a row is selected or unselected.

Yet another simple example:

gboolean
view_selection_func (GtkTreeSelection *selection,
                     GtkTreeModel     *model,
                     GtkTreePath      *path,
                     gboolean          path_currently_selected,
                     gpointer          userdata)
{
  GtkTreeIter iter;

  if (gtk_tree_model_get_iter(model, &iter, path))
    {
      char *name;

      gtk_tree_model_get(model, &iter, COL_NAME, &name, -1);

      if (!path_currently_selected)
        g_print ("%s is going to be selected.\n", name);
      else
        g_print ("%s is going to be unselected.\n", name);

      g_free(name);
    }

  return TRUE; /* allow selection state to change */
}

void
create_view (void)
{
  GtkWidget *view;
  GtkTreeSelection *selection;

  // ...

  view = gtk_tree_view_new();

  // ...

  selection = gtk_tree_view_get_selection(GTK_TREE_VIEW(view));

  gtk_tree_selection_set_select_function(selection, view_selection_func, NULL, NULL);

  // ...
}

Checking Whether a Row is Selected

You can check whether a given row is selected or not using the functions gtk_tree_selection_iter_is_selected() or gtk_tree_selection_path_is_selected(). If you want to know all rows that are not selected, for example, you could just traverse the whole list or tree, and use the above functions to check for each row whether it is selected or not.

Selecting and Unselecting Rows

You can select or unselect rows manually with gtk_tree_selection_select_iter(), gtk_tree_selection_select_path(), gtk_tree_selection_unselect_iter(), gtk_tree_selection_unselect_path(), gtk_tree_selection_select_all(), and gtk_tree_selection_unselect_all() should you ever need to do that.

Getting the Number of Selected Rows

Sometimes you want to know the number of rows that are currently selected (for example to set context menu entries active or inactive before you pop up a context menu). If you are using selection mode GTK_SELECTION_SINGLE or GTK_SELECTION_BROWSE, this is trivial to check with gtk_tree_selection_get_selected(), which will return either TRUE or FALSE (meaning one selected row or no selected row).

If you are using GTK_SELECTION_MULTIPLE or want a more general approach that works for all selection modes, `gtk_tree_selection_count_selected_rows() will return the information you are looking for.

Double-Clicks on a Row

Catching double-clicks on a row is quite easy and is done by connecting to a tree view’s “row-activated” signal, like this:

void
view_onRowActivated (GtkTreeView        *treeview,
                     GtkTreePath        *path,
                     GtkTreeViewColumn  *col,
                     gpointer            userdata)
{
  GtkTreeModel *model;
  GtkTreeIter iter;

  g_print ("A row has been double-clicked!\n");

  model = gtk_tree_view_get_model(treeview);

  if (gtk_tree_model_get_iter(model, &iter, path))
    {
      char *name;

      gtk_tree_model_get(model, &iter, COLUMN_NAME, &name, -1);

      g_print ("Double-clicked row contains name %s\n", name);

      g_free(name);
    }
}

void
create_view (void)
{
  GtkWidget *view = gtk_tree_view_new();

  // ...

  g_signal_connect(view, "row-activated", G_CALLBACK(view_onRowActivated-, NULL);

  // ...
}

Context Menus on Right Click

Context menus are context-dependent menus that pop up when a user right-clicks on a list or tree and usually let the user do something with the selected items or manipulate the list or tree in other ways.

Right-clicks on a tree view are caught just like mouse button clicks are caught with any other widgets, namely by connecting to the tree view’s “button-press-event” signal handler (which is a GtkWidget signal, and as GtkTreeView is derived from GtkWidget it has this signal as well). Additionally, you should also connect to the “popup-menu” signal, so users can access your context menu without a mouse. The “popup-menu” signal is emitted when the user presses Shift-F10. Also, you should make sure that all functions provided in your context menu can also be accessed by other means such as the application’s main menu. See the GNOME Human Interface Guidelines for more details.

Straight from the a-snippet-of-code-says-more-than-a-thousand-words-department, some code to look at:

void
view_popup_menu_onDoSomething (GtkWidget *menuitem,
                               gpointer userdata)
{
  /* we passed the view as userdata when we connected the signal */
  GtkTreeView *treeview = GTK_TREE_VIEW(userdata);

  g_print ("Do something!\n");
}

void
view_popup_menu (GtkWidget *treeview,
                 GdkEventButton *event,
         gpointer userdata)
{
  GtkWidget *menu, *menuitem;

  menu = gtk_menu_new();

  menuitem = gtk_menu_item_new_with_label("Do something");

  g_signal_connect(menuitem, "activate",
                   (GCallback) view_popup_menu_onDoSomething, treeview);

  gtk_menu_shell_append(GTK_MENU_SHELL(menu), menuitem);

  gtk_widget_show_all(menu);

  /* Note: event can be NULL here when called from view_onPopupMenu;
   * gdk_event_get_time() accepts a NULL argument
   */
  gtk_menu_popup(GTK_MENU(menu), NULL, NULL, NULL, NULL,
                 (event != NULL) ? event->button : 0,
                 gdk_event_get_time((GdkEvent*)event));
}

gboolean
view_onButtonPressed (GtkWidget *treeview,
                      GdkEventButton *event,
              gpointer userdata)
{
  /* single click with the right mouse button? */
  if (event->type == GDK_BUTTON_PRESS  &&  event->button == 3)
  {
    g_print ("Single right click on the tree view.\n");

    /* optional: select row if no row is selected or only
     *  one other row is selected (will only do something
     *  if you set a tree selection mode as described later
     *  in the tutorial) */
    if (1)
    {
      GtkTreeSelection *selection;

      selection = gtk_tree_view_get_selection(GTK_TREE_VIEW(treeview));

      /* Note: gtk_tree_selection_count_selected_rows() does not
       *   exist in gtk+-2.0, only in gtk+ >= v2.2 ! */
      if (gtk_tree_selection_count_selected_rows(selection)  <= 1)
      {
         GtkTreePath *path;

         /* Get tree path for row that was clicked */
         if (gtk_tree_view_get_path_at_pos(GTK_TREE_VIEW(treeview),
                                           (gint) event->x, 
                                           (gint) event->y,
                                           &path, NULL, NULL, NULL))
         {
           gtk_tree_selection_unselect_all(selection);
           gtk_tree_selection_select_path(selection, path);
           gtk_tree_path_free(path);
         }
      }
    } /* end of optional bit */

    view_popup_menu(treeview, event, userdata);

    return GDK_EVENT_STOP;
  }

  return GDK_EVENT_PROPAGATE;
}

gboolean
view_onPopupMenu (GtkWidget *treeview,
                  gpointer userdata)
{
  view_popup_menu(treeview, NULL, userdata);

  return GDK_EVENT_STOP
}

void
create_view (void)
{
  GtkWidget *view = gtk_tree_view_new();

  // ...

  g_signal_connect(view, "button-press-event", G_CALLBACK(view_onButtonPressed), NULL);
  g_signal_connect(view, "popup-menu", G_CALLBACK(view_onPopupMenu), NULL);

  // ...
}

Sorting

Lists and trees are meant to be sorted. This is done using the GtkTreeSortable interface that can be implemented by tree models. ‘Interface’ means that you can just cast a GtkTreeModel into a GtkTreeSortable with GTK_TREE_SORTABLE(model) and use the documented tree sortable functions on it, just like we did before when we cast a list store to a tree model and used the gtk_tree_model_foo() family of functions. Both GtkListStore and GtkTreeStore implement the tree sortable interface.

The most straight forward way to sort a list store or tree store is to directly use the tree sortable interface on them. This will sort the store in place, meaning that rows will actually be reordered in the store if required. This has the advantage that the position of a row in the tree view will always be the same as the position of a row in the model, in other words: a tree path refering to a row in the view will always refer to the same row in the model, so you can get a row’s iter easily with gtk_tree_model_get_iter() using a tree path supplied by the tree view. This is not only convenient, but also sufficient for most scenarios.

However, there are cases when sorting a model in place is not desirable, for example when several tree views display the same model with different sortings, or when the unsorted state of the model has some special meaning and needs to be restored at some point. This is where GtkTreeModelSort comes in, which is a special model that maps the unsorted rows of a child model (e.g. a list store or tree store) into a sorted state without changing the child model.

GtkTreeSortable

The tree sortable interface is fairly simple and should be easy to use. Basically you define a ‘sort column ID’ integer for every criterion you might want to sort by and tell the tree sortable which function should be called to compare two rows (represented by two tree iters) for every sort ID with gtk_tree_sortable_set_sort_func(). Then you sort the model by setting the sort column ID and sort order with gtk_tree_sortable_set_sort_column_id(), and the model will be re-sorted using the compare function you have set up. Your sort column IDs can correspond to your model columns, but they do not have to (you might want to sort according to a criterion that is not directly represented by the data in one single model column, for example). Some code to illustrate this:

enum
{
  COL_NAME = 0,
  COL_YEAR_BORN
};

enum
{
  SORTID_NAME = 0,
  SORTID_YEAR
};

GtkTreeModel  *liststore = NULL;

void
toolbar_onSortByYear (void)
{
  GtkTreeSortable *sortable;
  GtkSortType order;
  int sortid;

  sortable = GTK_TREE_SORTABLE(liststore);

  /* If we are already sorting by year, reverse sort order,
   * otherwise set it to year in ascending order
   */
  if (gtk_tree_sortable_get_sort_column_id(sortable, &sortid, &order) &&
      sortid == SORTID_YEAR)
    {
      GtkSortType neworder;

      neworder = (order == GTK_SORT_ASCENDING) ? GTK_SORT_DESCENDING : GTK_SORT_ASCENDING;

      gtk_tree_sortable_set_sort_column_id(sortable, SORTID_YEAR, neworder);
    }
  else
    {
      gtk_tree_sortable_set_sort_column_id(sortable, SORTID_YEAR, GTK_SORT_ASCENDING);
    }
}

/* This is not pretty. Of course you can also use a
 * separate compare function for each sort ID value
 */
int
sort_iter_compare_func (GtkTreeModel *model,
                        GtkTreeIter  *a,
                        GtkTreeIter  *b,
                        gpointer      userdata)
{
  int sortcol = GPOINTER_TO_INT(userdata);
  int ret = 0;

  switch (sortcol)
    {
    case SORTID_NAME:
      {
        char *name1, *name2;

        gtk_tree_model_get(model, a, COL_NAME, &name1, -1);
        gtk_tree_model_get(model, b, COL_NAME, &name2, -1);

        if (name1 == NULL || name2 == NULL)
          {
            if (name1 == NULL && name2 == NULL)
              break; /* both equal => ret = 0 */

            ret = (name1 == NULL) ? -1 : 1;
          }
        else
          {
            ret = g_utf8_collate(name1,name2);
          }

        g_free(name1);
        g_free(name2);
      }
      break;

    case SORTID_YEAR:
      {
        guint year1, year2;

        gtk_tree_model_get(model, a, COL_YEAR_BORN, &year1, -1);
        gtk_tree_model_get(model, b, COL_YEAR_BORN, &year2, -1);

        if (year1 != year2)
          {
            ret = (year1 > year2) ? 1 : -1;
          }
        /* else both equal => ret = 0 */
      }
      break;

    default:
      g_return_val_if_reached(0);
    }

  return ret;
}

void
create_list_and_view (void)
{
  GtkTreeSortable *sortable;

  // ...

  liststore = gtk_list_store_new(2, G_TYPE_STRING, G_TYPE_UINT);

  sortable = GTK_TREE_SORTABLE(liststore);

  gtk_tree_sortable_set_sort_func(sortable, SORTID_NAME, sort_iter_compare_func,
                                  GINT_TO_POINTER(SORTID_NAME), NULL);

  gtk_tree_sortable_set_sort_func(sortable, SORTID_YEAR, sort_iter_compare_func,
                                  GINT_TO_POINTER(SORTID_YEAR), NULL);

  // set initial sort order
  gtk_tree_sortable_set_sort_column_id(sortable, SORTID_NAME, GTK_SORT_ASCENDING);

  // ...

  view = gtk_tree_view_new_with_model(liststore);

  // ...
}

Usually things are a bit easier if you make use of the tree view column headers for sorting, in which case you only need to assign sort column IDs and your compare functions, but do not need to set the current sort column ID or order yourself (see below).

Your tree iter compare function should return a negative value if the row specified by iter a comes before the row specified by iter b, and a positive value if row b comes before row a. It should return 0 if both rows are equal according to your sorting criterion (you might want to use a second sort criterion though to avoid ‘jumping’ of equal rows when the store gets resorted). Your tree iter compare function should not take the sort order into account, but assume an ascending sort order (otherwise bad things will happen).

GtkTreeModelSort

GtkTreeModelSort is a wrapper tree model. It takes another tree model such as a list store or a tree store as child model, and presents the child model to the ‘outside’ (ie. a tree view or whoever else is accessing it via the tree model interface) in a sorted state. It does that without changing the order of the rows in the child model. This is useful if you want to display the same model in different tree views with different sorting criteria for each tree view, for example, or if you need to restore the original unsorted state of your store again at some point.

GtkTreeModelSort implements the GtkTreeSortable interface, so you can treat it just as if it was your data store for sorting purposes. Here is the basic setup with a tree view:

void
create_list_and_view (void)
{
  // ...

  liststore = gtk_list_store_new(2, G_TYPE_STRING, G_TYPE_UINT);

  sortmodel = gtk_tree_model_sort_new_with_model(liststore);

  gtk_tree_sortable_set_sort_func(GTK_TREE_SORTABLE(sortmodel), SORTID_NAME,
                                  sort_func, GINT_TO_POINTER(SORTID_NAME), NULL);

  gtk_tree_sortable_set_sort_func(GTK_TREE_SORTABLE(sortmodel), SORTID_YEAR,
                                  sort_func, GINT_TO_POINTER(SORTID_YEAR), NULL);

  // set initial sort order
  gtk_tree_sortable_set_sort_column_id(GTK_TREE_SORTABLE(sortmodel),
                                       SORTID_NAME, GTK_SORT_ASCENDING);

  // ...

  view = gtk_tree_view_new_with_model(sortmodel);

  //...
}

However, when using the sort tree model, you need to be careful when you use iters and paths with the model. This is because a path pointing to a row in the view (and the sort tree model here) does probably not point to the same row in the child model which is your original list store or tree store, because the row order in the child model is probably different from the sorted order. Similarly, an iter that is valid for the sort tree model is not valid for the child model, and vice versa. You can convert paths and iters from and to the child model using gtk_tree_model_sort_convert_child_path_to_path(), gtk_tree_model_sort_convert_child_iter_to_iter(), gtk_tree_model_sort_convert_path_to_child_path(), and gtk_tree_model_sort_convert_iter_to_child_iter(). You are unlikely to need these functions frequently though, as you can still directly use gtk_tree_model_get() on the sort tree model with a path supplied by the tree view.

For the tree view, the sort tree model is the ‘real’ model - it knows nothing about the sort tree model’s child model at all, which means that any path or iter that you get passed from the tree view in a callback or otherwise will refer to the sort tree model, and that you need to pass a path or iter refering to the sort tree model as well if you call tree view functions.

Sorting and Tree View Column Headers

Unless you have hidden your tree view column headers or use custom tree view column header widgets, each tree view column’s header can be made clickable. Clicking on a tree view column’s header will then sort the list according to the data in that column. You need to do two things to make this happen: firstly, you need to tell your model which sort function to use for which sort column ID with gtk_tree_sortable_set_sort_func(). Once you have done this, you tell each tree view column which sort column ID should be active if this column’s header is clicked. This is done with gtk_tree_view_column_set_sort_column_id().

And that is really all you need to do to get your list or tree sorted. The tree view columns will automatically set the active sort column ID and sort order for you if you click on a column header.

Case-insensitive String Comparing

As described above in the “GtkCellRendererText, UTF8, and Pango markup” section, all strings that are to be displayed in the tree view need to be encoded in UTF8 encoding. All ASCII strings are valid UTF8, but as soon as non-ASCII characters are used, things get a bit tricky and the character encoding matters.

Comparing two ASCII strings ignoring the case is trivial and can be done using g_ascii_strcasecmp(), for example. strcasecmp will usually do the same, only that it is also locale-aware to some extent. The only problem is that a lot of users use locale character encodings that are not UTF8, so strcasecmp does not take us very far.

g_utf8_collate() will compare two strings in UTF8 encoding, but it does not ignore the case. In order to achieve at least half-way correct linguistic case-insensitive sorting, we need to take a two-step approach. For example, we could use g_utf8_casefold() to convert the strings to compare into a form that is independent of case, and then use g_utf8_collate() to compare those two strings (note that the strings returned by g_utf8_casefold() will not resemble the original string in any recognisable way; they will work fine for comparisons though). Alternatively, one could use g_utf8_strdown() on both strings and then compare the results again with g_utf8_collate().

Obviously, all this is not going to be very fast, and adds up if you have a lot of rows. To speed things up, you can create a ‘collation key’ with g_utf8_collate_key() and store that in your model as well. A collation key is just a string that does not mean anything to us, but can be used with strcmp for string comparison purposes (which is a lot faster than g_utf8_collate()).

It should be noted that the way g_utf8_collate() sorts is dependent on the current locale. Make sure you are not working in the ‘C’ locale (=default, none specified) before you are wondering about weird sorting orders. Check with echo $LANG on a command line what you current locale is set to.

Check out the “Unicode Manipulation” section in the GLib API Reference for more details.

Editable Cells

Editable Text Cells

With GtkCellRendererText you can not only display text, but you can also allow the user to edit a single cell’s text right in the tree view by double-clicking on a cell.

To make this work you need to tell the cell renderer that a cell is editable, which you can do by setting the “editable” property of the text cell renderer in question to TRUE. You can either do this on a per-row basis (which allows you to set each single cell either editable or not) by connecting the “editable” property to a boolean type column in your tree model using attributes; or you can just use:

g_object_set(renderer, "editable", TRUE, NULL);

when you create the renderer, which sets all rows in that particular renderer column to be editable.

Now that our cells are editable, we also want to be notified when a cell has been edited. This can be achieved by connecting to the cell renderer’s “edited” signal:

g_signal_connect(renderer, "edited", G_CALLBACK(cell_edited_callback), NULL);

This callback is then called whenever a cell has been edited. Instead of NULL we could have passed a pointer to the model as user data for convenience, as we probably want to store the new value in the model.

The callback for the “edited” signal looks like this (the API reference is a bit lacking in this particular case):

void
cell_edited_callback (GtkCellRendererText *cell,
                      char                *path_string,
                      char                *new_text,
                      gpointer             user_data);

The tree path is passed to the “edited” signal callback in string form. You can convert this into a GtkTreePath with gtk_tree_path_new_from_string(), or convert it into an iter with gtk_tree_model_get_iter_from_string().

Note that the cell renderer will not change the data for you in the store. After a cell has been edited, you will only receive an “edited” signal. If you do not change the data in the store, the old text will be rendered again as if nothing had happened.

If you have multiple (renderer) columns with editable cells, it is not necessary to have a different callback for each renderer, you can use the same callback for all renderers, and attach some data to each renderer, which you can later retrieve again in the callback to know which renderer/column has been edited. This is done like this, for example:

renderer = gtk_cell_renderer_text_new();
g_object_set_data(G_OBJECT(renderer),
                  "my_column_num",
                  GUINT_TO_POINTER(COLUMN_NAME));

...

renderer = gtk_cell_renderer_text_new();
g_object_set_data(G_OBJECT(renderer),
                  "my_column_num",
                  GUINT_TO_POINTER(COLUMN_YEAR_OF_BIRTH));

where COLUMN_NAME and COLUMN_YEAR_OF_BIRTH are enum values. In your callback you can then get the column number with

guint column_number =
  GPOINTER_TO_UINT(g_object_get_data(G_OBJECT(renderer), "my_column_num"));

You can use this mechanism to attach all kinds of custom data to any object or widget, with a string identifier to your liking.

Setting the cursor to a specific cell

You can move the cursor to a specific cell in a tree view with gtk_tree_view_set_cursor() (or gtk_tree_view_set_cursor_on_cell() if you have multiple editable cell renderers packed into one tree view column), and start editing the cell if you want to. Similarly, you can get the current row and focus column with gtk_tree_view_get_cursor(). Use gtk_widget_grab_focus(treeview) will make sure that the tree view has the keyboard focus.

As the API reference points out, the tree view needs to be realised for cell editing to happen. In other words: If you want to start editing a specific cell right at program startup, you need to set up an idle timeout with g_idle_add() that does this for you as soon as the window and everything else has been realised (return G_SOURCE_REMOVE in the timeout to make it run only once). Alternatively you could connect to the “realize” signal of the treeview with g_signal_connect_after() to achieve the same thing.

Connect to the tree view’s “cursor-changed” and/or “move-cursor” signals to keep track of the current position of the cursor.

Editable Toggle and Radio Button Cells

Just like you can set a GtkCellRendererText editable, you can specify whether a GtkCellRendererToggle should change its state when clicked by setting the “activatable” property - either when you create the renderer (in which case all cells in that column will be clickable) or by connecting the renderer property to a model column of boolean type via attributes.

Connect to the “toggled” signal of the toggle cell renderer to be notified when the user clicks on a toggle button (or radio button). The user click will not change the value in the store, or the appearance of the value rendered. The toggle button will only change state when you update the value in the store. Until then it will be in an “inconsistent” state, which is also why you should read the current value of that cell from the model, and not from the cell renderer.

The callback for the “toggled” signal looks like this (the API reference is a bit lacking in this particular case):

void
cell_toggled_callback (GtkCellRendererToggle *cell,
                       char                  *path_string,
                       gpointer               user_data);

Just like with the “edited” signal of the text cell renderer, the tree path is passed to the “toggled” signal callback in string form. You can convert this into a GtkTreePath with gtk_tree_path_new_from_string(), or convert it into an iter with gtk_tree_model_get_iter_from_string().

Editable Spin Button Cells

GTK provides a GtkCellRendererSpin cell renderer, which exposes a spin button when editing its contents. You must provide a GtkAdjustment object to control the range of appropriate values, as well as the increments to be applied.

Miscellaneous

This section deals with issues and questions that did not seem to fit in anywhere else in the tutorial.

Getting the Column Number from a Tree View Column Widget

Signal callbacks often only get passed a pointer to a GtkTreeViewColumn when the application programmer really just wants to know which column number was affected. There are two ways to find out the position of a column within the tree view. One way is to write a small helper function that looks up the column number from a given tree view column object, like this for example:

/* Returns column number or -1 if not found or on error */

int
get_col_number_from_tree_view_column (GtkTreeViewColumn *col)
{
  GList *cols;
  int num;

  g_return_val_if_fail ( col != NULL, -1 );
  g_return_val_if_fail ( col->tree_view != NULL, -1 );

  cols = gtk_tree_view_get_columns(GTK_TREE_VIEW(col->tree_view));

  num = g_list_index(cols, (gpointer) col);

  g_list_free(cols);

  return num;
}

Alternatively, it is possible to use g_object_set_data() and g_object_get_data() on the tree view column in order to identify which column it is. This also has the advantage that you can still keep track of your columns even if the columns get re-ordered within the tree view (a feature which is usually disabled though). Use like this:

...

enum
{
  COL_FIRSTNAME,
  COL_SURNAME,
};

...

void
some_callback (GtkWidget *treeview, ..., GtkTreeViewColumn *col, ...)
{
  guint colnum = GPOINTER_TO_UINT(g_object_get_data(G_OBJECT(col), "columnnum"));

  ...
}

void
create_view(void)
{
  ...
  col = gtk_tree_view_column_new();
  g_object_set_data(G_OBJECT(col), "columnnum", GUINT_TO_POINTER(COL_FIRSTNAME));
  ...
  col = gtk_tree_view_column_new();
  g_object_set_data(G_OBJECT(col), "columnnum", GUINT_TO_POINTER(COL_SURNAME));
  ...
}

columnnum” is a random string in the above example - you can use whatever string you want instead, or store multiple bits of data (with different string identifiers of course). Of course you can also combine both approaches, as they do slightly different things (the first tracks the ‘physical’ position of a column within the tree view, the second tracks the ‘meaning’ of a column to you, independent of its position within the view).

Column Expander Visibility

Hiding the Column Expander

Is it possible to hide the column expander completely? Yes and no. What follows, is probably a dirty hack at best and there is no guarantee that it will work with upcoming Gtk+ versions or even with all past versions (although the latter is easy enough to test of course).

What you can do to hide the column expander is to create an empty tree view column (containing empty strings, for example) and make this the first column in the tree view. Then you can hide that column with gtk_tree_view_column_set_visible(). You will notice that the expander column will now automatically move to the formerly second, now first, visible column in the tree view. However, if you call gtk_tree_view_set_expander_column() right after the call to set_visible(), then the expander will move back to the hidden column, and no expander is visible any longer.

This means of course that you will have to take care of expanding and collapsing rows yourself and use the appropriate tree view functions. While it is at last thinkable that one could implement custom expanders using custom cell rendereres or pixbuf cell renderers, this is probably a task that will keep you busy for more than five minutes. Keep those head ache tablets nearby if you attempt it anyway…

Forcing Column Expander Visibility

There are situations where an expander should be visible even if the row in question does not have any children yet, for instance when part of a model should only be loaded on request when a node gets expanded (e.g. to show the contents of a directory). This is not possible. An expander is only shown if a node has children.

A work-around for this problem exists however: simply attach an empty child row and set the node to collapsed state. Then listen for the tree view’s “row-expanded” signal, and fill the contents of the already existing row with the first new row, then append new child rows.

Getting the Cell Renderer a Click Event Happened On

It seems that in many cases when people want to know the cell renderer a click event happened on, they do not really need to know the cell renderer, but rather want to modify an individual cell in a particular column. For this you do not need to know the cell renderer. Use gtk_tree_view_get_path_at_pos to get a tree path from the x and y coordinates of the button event that is passed to you in a “button-press-event” signal callback (if you use the “row-activated” signal to catch double-clicks you get the tree path passed directly into the callback function). Then convert that tree path into an iter using gtk_tree_model_get_iter and modify the data in the cell you want to modify with gtk_list_store_set or gtk_tree_store_set.

If you really do need to know the cell renderer where a button press event happened, that is a bit more tricky. Here is a suggestion on how to approach this issue:

static gboolean
tree_view_get_cell_from_pos (GtkTreeView *view,
                             guint x,
                 guint y,
                 GtkCellRenderer **cell)
{
  GtkTreeViewColumn *col = NULL;
  GList *node, *columns, *cells;
  guint colx = 0;

  /* (1) find column and column x relative to tree view coordinates */
  columns = gtk_tree_view_get_columns(view);

  for (node = columns;  node != NULL && col == NULL;  node = node->next)
    {
      GtkTreeViewColumn *checkcol = node->data;

      if (x >= colx  &&  x < (colx + checkcol->width))
        col = checkcol;
      else
        colx += checkcol->width;
    }

  g_list_free(columns);

  if (col == NULL)
    return FALSE; /* not found */

  /* (2) find the cell renderer within the column */
  cells = gtk_tree_view_column_get_cell_renderers(col);

  for (node = cells;  node != NULL;  node = node->next)
    {
      GtkCellRenderer *checkcell = node->data;
      guint width = 0, height = 0;

      /* Will this work for all packing modes? doesn't that
       *  return a random width depending on the last content
       * rendered? */
      gtk_cell_renderer_get_size(checkcell, GTK_WIDGET(view), NULL, NULL, NULL, &width, NULL);

      if (x >= colx && x < (colx + width))
        {
      *cell = checkcell;
      g_list_free(cells);
      return TRUE;
        }

      colx += width;
    }

  g_list_free(cells);
  return FALSE; /* not found */
}

static gboolean
onButtonPress (GtkWidget *view,
               GdkEventButton *bevent,
           gpointer data)
{
  GtkCellRenderer *renderer = NULL;

  if (tree_view_get_cell_from_pos(GTK_TREE_VIEW(view), bevent->x, bevent->y, &renderer))
    g_print ("Renderer found\n");
  else
    g_print ("Renderer not found!\n");
}

Writing Custom Models

When is a Custom Model Useful?

A custom tree model gives you complete control over your data and how it is represented to the outside (e.g. to the tree view widget). It has the advantage that you can store, access and modify your data exactly how you need it, and you can optimise the way your data is stored and retrieved, as you can write your own functions to access your data and need not rely solely on the gtk_tree_model_get. A model tailored to your needs will probably also be a lot faster than the generic list and tree stores that come with gtk and that have been designed with flexibility in mind.

Another case where a custom model might come in handy is when you have all your data already stored in an external tree-like structure (for example a libxml2 XML tree) and only want to display that structure. Then you could write a custom model that maps that structure to a tree model (which is probably not quite as trivial as it sounds though).

Using a custom model you could also implement a filter model that only displays certain rows according to some filter criterion instead of displaying all rows (GTK has a filter model, GtkTreeModelFilter, that does exactly that and much more, but you might want to implement this yourself anyway.)

However, all this comes at a cost: you are unlikely to write a useful custom model in less than a thousand lines, unless you strip all newline characters. Writing a custom model is not as difficult as it might sound though, and it may well be worth the effort, not least because it will result in much saner code if you have a lot of data to keep track of.

What Does Writing a Custom Model Involve?

Basically, all you need to do is to write a new GObject that implements the GtkTreeModel interface, GtkTreeModelIface. Intimate knowledge about the GLib GObject system is not a requirement - you just need to copy some boilerplate code and modify it a bit. The core of your custom tree model is your own implementation of a couple of gtk_tree_model_foo functions that reveal the structure of your data, ie. how many rows there are, how many children a row has, how many columns there are and what type of data they contain. Furthermore, you need to provide functions that convert a tree path to a tree iter and a tree iter to a tree path. Additionally, you should provide some functions to add and remove rows to your custom model, but those are only ever used by yourself anyway, so they do not fall within the scope of the tree model interface.

The functions you need to implement are:

  • get_flags: tells the outside that your model has certain special characterstics, like persistent iters.
  • get_n_columns: how many data fields per row are visible to the outside that uses gtk_tree_model_get, e.g. cell renderer attributes
  • get_column_type: what type of data is stored in a data field (model column) that is visible to the outside
  • get_iter: take a tree path and fill an iter structure so that you know which row it refers to
  • get_path: take an iter and convert it into a tree path, ie. the ‘physical’ position within the model
  • get_value: retrieve data from a row
  • iter_next: take an iter structure and make it point to the next row
  • iter_children: tell whether the row represented by a given iter has any children or not
  • iter_n_children: tell how many children a row represented by a given iter has
  • iter_nth_child: set a given iter structure to the n-th child of a given parent iter
  • iter_parent: set a given iter structure to the parent of a given child iter

It is up to you to decide which of your data you make ‘visible’ to the outside in form of model columns and which not. You can always implement functions specific to your custom model that will return any data in any form you desire. You only need to make data ‘visble’ to the outside via the GType and GValue system if you want the tree view components to access it (e.g. when setting cell renderer attributes).

Example: A Simple Custom List Model

What follows is the outline for a simple custom list model. You can find the complete source code for this model below. The beginning of the code might look a bit scary, but you can just skip most of the GObject and GType stuff and proceed to the heart of the custom list, ie. the implementation of the tree model functions.

Our list model is represented by a simple list of records, where each row corresponds to a CustomRecord structure which keeps track of the data we are interested in. For now, we only want to keep track of persons’ names and years of birth (usually this would not really justify a custom model, but this is still just an example). It is trivial to extend the model to deal with additional fields in the CustomRecord structure.

Within the model, more precisely: the CustomList structure, the list is stored as a pointer array, which not only provides fast access to the n-th record in the list, but also comes in handy later on when we add sorting. Apart from that, any other kind of list-specific data would go in this structure as well (the active sort column, for example, or hash tables to speed up searching for a specific row, etc.).

Each row in our list is represented by a CustomRecord structure. You can store whatever other data you need in that structure. How you make row data available is up to you. Either you export it via the tree model interface using the GValue system, so that you can use gtk_tree_model_get to retrieve your data, or you provide custom model-specific functions to retrieve data, for example custom_list_get_name, taking a tree iter or a tree path as argument. Of course you can also do both.

Furthermore, you will need to provide your own functions to add rows, remove rows, and set or modify row data, and you need to let the view and others know whenever something changes in your model by emitting the appropriate signals via the provided tree model functions.

Some thought should go into how exactly you fill the GtkTreeIter fields of the tree iters used by your model. You have three pointer fields at your disposal. These should be filled so that you can easily identify the row given the iter, and should also facilitate access to the next row and the parent row (if any). If your model advertises to have persistent iters, you need to make sure that the content of your iters is perfectly valid even if the user stores it somewhere for later use and the model gets changed or reordered. The ‘stamp’ field of a tree iter should be filled by a random model-instance-specific integer that was assigned to the model when it was created. This way you can catch iters that do not belong to your model. If your model does not have persistent iters, then you should change the model’s stamp whenever the model changes, so that you can catch invalid iters that get passed to your functions (note: in the code below we do not check the stamp of the iters in order to save a couple of lines of code to print here).

In our specific example, we simply store a pointer to a row’s CustomRecord structure in our model’s tree iters, which is valid as long as the row exists. Additionally we store the position of a row within the list in the CustomRecord as well, which is not only intuitive, but is also useful later on when we resort the list.

If you want to store an integer value in an iter’s fields, you should use GLib’s GINT_TO_POINTER and GPOINTER_TO_INT macros for that.

Writing Custom Cell Renderers

The cell renderers that come with GTK should be sufficient for most purposes, but there might be occasions where you want to display something in a tree view that you cannot display with the provided cell renderers, or where you want to derive from one of the provided cell renderers to extend its functionality.

You can do this by writing a new object that derives from GtkCellRenderer (or even one of the other cell renderers if you just want to extend an existing one).

Three things you need to do in the course of that:

  • Register some new properties that your renderer needs with the type system and write your own set_property and get_property functions to set and get your new renderer’s properties.
  • Write your own cell_renderer_get_size function and override the parent object’s function (usually the parent is of type GtkCellRenderer. Note that you should honour the standard properties for padding and cell alignment of the parent object here.
  • Write your own cell_renderer_render function and override the parent object’s function. This function does the actual rendering.

The GObject type system stuff of writing a new cell renderer is similar to what we have done above when writing a custom tree model, and is relatively straight forward in this case. Copy and paste and modify according to your own needs.

Good examples of cell renderer code to look at or even modify are GtkCellRendererPixbuf and GtkCellRendererToggle in the Gtk+ source code tree. Both cases are less than five hundred lines of code to look at and thus should be fairly easy to digest.

Working Example: a Progress Bar Cell Renderer

In the following we will write a custom cell renderer to render progress bars into a tree view (the code was “heavily inspired” by Sean Egan’s progress bar cell renderer implementation in GAIM; note this is merely for demonstrational purposes, GTK has had a progress bar cell renderer for quite a while now: see the GtkCellRendererProgress API documentation for more details).