GtkLayoutManager

Layout managers are delegate classes that handle the preferred size and the allocation of a widget.

You typically subclass gtk.layout_manager.LayoutManager if you want to implement a layout policy for the children of a widget, or if you want to determine the size of a widget depending on its contents.

Each gtk.widget.Widget can only have a gtk.layout_manager.LayoutManager instance associated to it at any given time; it is possible, though, to replace the layout manager instance using gtk.widget.Widget.setLayoutManager.

Layout properties

A layout manager can expose properties for controlling the layout of each child, by creating an object type derived from gtk.layout_child.LayoutChild and installing the properties on it as normal gobject.object.ObjectG properties.

Each gtk.layout_child.LayoutChild instance storing the layout properties for a specific child is created through the gtk.layout_manager.LayoutManager.getLayoutChild method; a gtk.layout_manager.LayoutManager controls the creation of its gtk.layout_child.LayoutChild instances by overriding the GtkLayoutManagerClass.create_layout_child() virtual function. The typical implementation should look like:

static GtkLayoutChild *
create_layout_child (GtkLayoutManager *manager,
                     GtkWidget        *container,
                     GtkWidget        *child)
{
  return g_object_new (your_layout_child_get_type (),
                       "layout-manager", manager,
                       "child-widget", child,
                       NULL);
}

The property@Gtk.LayoutChild:layout-manager and property@Gtk.LayoutChild:child-widget properties on the newly created gtk.layout_child.LayoutChild instance are mandatory. The gtk.layout_manager.LayoutManager will cache the newly created gtk.layout_child.LayoutChild instance until the widget is removed from its parent, or the parent removes the layout manager.

Each gtk.layout_manager.LayoutManager instance creating a gtk.layout_child.LayoutChild should use gtk.layout_manager.LayoutManager.getLayoutChild every time it needs to query the layout properties; each gtk.layout_child.LayoutChild instance should call gtk.layout_manager.LayoutManager.layoutChanged every time a property is updated, in order to queue a new size measuring and allocation.