LayoutManager

class LayoutManager(**properties: Any)

Superclasses: Object

Subclasses: BinLayout, BoxLayout, CenterLayout, ConstraintLayout, CustomLayout, FixedLayout, GridLayout, OverlayLayout

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 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 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 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 layout_manager and 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 get_layout_child every time it needs to query the layout properties; each GtkLayoutChild instance should call layout_changed every time a property is updated, in order to queue a new size measuring and allocation.

Methods

class LayoutManager

allocate(widget: Widget, width: int, height: int, baseline: int) → None

Assigns the given width, height, and baseline to a widget, and computes the position and sizes of the children of the widget using the layout management policy of manager.

Parameters:

widget – the GtkWidget using manager
width – the new width of the widget
height – the new height of the widget
baseline – the baseline position of the widget, or -1

get_layout_child(child: Widget) → LayoutChild

Retrieves a GtkLayoutChild instance for the GtkLayoutManager, creating one if necessary.

The child widget must be a child of the widget using manager.

The GtkLayoutChild instance is owned by the GtkLayoutManager, and is guaranteed to exist as long as child is a child of the GtkWidget using the given GtkLayoutManager.

Parameters:: child – a GtkWidget

get_request_mode() → SizeRequestMode: Retrieves the request mode of manager.

get_widget() → Widget | None: Retrieves the GtkWidget using the given GtkLayoutManager.

layout_changed() → None

Queues a resize on the GtkWidget using manager, if any.

This function should be called by subclasses of GtkLayoutManager in response to changes to their layout management policies.

measure(widget: Widget, orientation: Orientation, for_size: int) → tuple[int, int, int, int]

Measures the size of the widget using manager, for the given orientation and size.

See the Widget documentation on layout management for more details.

Parameters:

widget – the GtkWidget using manager
orientation – the orientation to measure
for_size – Size for the opposite of orientation; for instance, if the orientation is HORIZONTAL, this is the height of the widget; if the orientation is VERTICAL, this is the width of the widget. This allows to measure the height for the given width, and the width for the given height. Use -1 if the size is not known

Virtual Methods

class LayoutManager

do_allocate(widget: Widget, width: int, height: int, baseline: int) → None

Assigns the given width, height, and baseline to a widget, and computes the position and sizes of the children of the widget using the layout management policy of manager.

Parameters:

widget – the GtkWidget using manager
width – the new width of the widget
height – the new height of the widget
baseline – the baseline position of the widget, or -1

do_create_layout_child(widget: Widget, for_child: Widget) → LayoutChild

Create a GtkLayoutChild instance for the given for_child widget.

Parameters:

widget – the widget using the manager
for_child – the child of widget

do_get_request_mode(widget: Widget) → SizeRequestMode

a virtual function, used to return the preferred request mode for the layout manager; for instance, “width for height” or “height for width”; see GtkSizeRequestMode

Parameters:: widget

do_measure(widget: Widget, orientation: Orientation, for_size: int) → tuple[int, int, int, int]

Measures the size of the widget using manager, for the given orientation and size.

See the Widget documentation on layout management for more details.

Parameters:

widget – the GtkWidget using manager
orientation – the orientation to measure
for_size – Size for the opposite of orientation; for instance, if the orientation is HORIZONTAL, this is the height of the widget; if the orientation is VERTICAL, this is the width of the widget. This allows to measure the height for the given width, and the width for the given height. Use -1 if the size is not known

do_root() → None: a virtual function, called when the widget using the layout manager is attached to a GtkRoot

do_unroot() → None: a virtual function, called when the widget using the layout manager is detached from a GtkRoot

Fields

class LayoutManager

parent_instance