GtkDropTarget

GtkDropTarget is an event controller to receive Drag-and-Drop operations.

The most basic way to use a GtkDropTarget to receive drops on a widget is to create it via gtk_drop_target_new(), passing in the GType of the data you want to receive and connect to the GtkDropTarget::drop signal to receive the data:

static gboolean
on_drop (GtkDropTarget *target,
         const GValue  *value,
         double         x,
         double         y,
         gpointer       data)
{
  MyWidget *self = data;

  // Call the appropriate setter depending on the type of data
  // that we received
  if (G_VALUE_HOLDS (value, G_TYPE_FILE))
    my_widget_set_file (self, g_value_get_object (value));
  else if (G_VALUE_HOLDS (value, GDK_TYPE_PIXBUF))
    my_widget_set_pixbuf (self, g_value_get_object (value));
  else
    return FALSE;

  return TRUE;
}

static void
my_widget_init (MyWidget *self)
{
  GtkDropTarget *target =
    gtk_drop_target_new (G_TYPE_INVALID, GDK_ACTION_COPY);

  // This widget accepts two types of drop types: GFile objects
  // and GdkPixbuf objects
  gtk_drop_target_set_gtypes (target, (GType [2]) {
    G_TYPE_FILE,
    GDK_TYPE_PIXBUF,
  }, 2);

  g_signal_connect (target, "drop", G_CALLBACK (on_drop), self);
  gtk_widget_add_controller (GTK_WIDGET (self), GTK_EVENT_CONTROLLER (target));
}

GtkDropTarget supports more options, such as:

• rejecting potential drops via the GtkDropTarget::accept signal and the gtk_drop_target_reject() function to let other drop targets handle the drop
• tracking an ongoing drag operation before the drop via the GtkDropTarget::enter, GtkDropTarget::motion and GtkDropTarget::leave signals
• configuring how to receive data by setting the GtkDropTarget:preload property and listening for its availability via the GtkDropTarget:value property

However, GtkDropTarget is ultimately modeled in a synchronous way and only supports data transferred via GType. If you want full control over an ongoing drop, the GtkDropTargetAsync object gives you this ability.

While a pointer is dragged over the drop target’s widget and the drop has not been rejected, that widget will receive the GTK_STATE_FLAG_DROP_ACTIVE state, which can be used to style the widget.

If you are not interested in receiving the drop, but just want to update UI state during a Drag-and-Drop operation (e.g. switching tabs), you can use GtkDropControllerMotion.