LayoutManagerProtocol

public protocol LayoutManagerProtocol : ObjectProtocol

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

You typically subclass GtkLayoutManager 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 GtkWidget can only have a GtkLayoutManager instance associated to it at any given time; it is possible, though, to replace the layout manager instance using [methodGtk.Widget.set_layout_manager].

Layout properties

A layout manager can expose properties for controlling the layout of each child, by creating an object type derived from [classGtk.LayoutChild] and installing the properties on it as normal GObject properties.

Each GtkLayoutChild instance storing the layout properties for a specific child is created through the [methodGtk.LayoutManager.get_layout_child] method; a GtkLayoutManager controls the creation of its GtkLayoutChild 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 [propertyGtk.LayoutChild:layout-manager] and [propertyGtk.LayoutChild:child-widget] properties on the newly created GtkLayoutChild instance are mandatory. The GtkLayoutManager will cache the newly created GtkLayoutChild instance until the widget is removed from its parent, or the parent removes the layout manager.

Each GtkLayoutManager instance creating a GtkLayoutChild should use [methodGtk.LayoutManager.get_layout_child] every time it needs to query the layout properties; each GtkLayoutChild instance should call [methodGtk.LayoutManager.layout_changed] every time a property is updated, in order to queue a new size measuring and allocation.

The LayoutManagerProtocol protocol exposes the methods and properties of an underlying GtkLayoutManager instance. The default implementation of these can be found in the protocol extension below. For a concrete class that implements these methods and properties, see LayoutManager. Alternatively, use LayoutManagerRef as a lighweight, unowned reference if you already have an instance you just want to use.