GtkContainer

## GtkContainer GtkContainer — Base class for widgets which contain other widgets |

## Synopsis

    #include <gtk/gtk.h>

    struct      GtkContainer;
    #define     GTK_IS_RESIZE_CONTAINER         (widget)
    #define     GTK_CONTAINER_WARN_INVALID_CHILD_PROPERTY_ID(object, property_id, pspec)
    #define     gtk_container_border_width
    void        gtk_container_add               (GtkContainer *container,
                                                 GtkWidget *widget);
    void        gtk_container_remove            (GtkContainer *container,
                                                 GtkWidget *widget);
    void        gtk_container_add_with_properties
                                                (GtkContainer *container,
                                                 GtkWidget *widget,
                                                 const gchar *first_prop_name,
                                                 ...);
    GtkResizeMode gtk_container_get_resize_mode (GtkContainer *container);
    void        gtk_container_set_resize_mode   (GtkContainer *container,
                                                 GtkResizeMode resize_mode);
    void        gtk_container_check_resize      (GtkContainer *container);
    void        gtk_container_foreach           (GtkContainer *container,
                                                 GtkCallback callback,
                                                 gpointer callback_data);
    void        gtk_container_foreach_full      (GtkContainer *container,
                                                 GtkCallback callback,
                                                 GtkCallbackMarshal marshal,
                                                 gpointer callback_data,
                                                 GtkDestroyNotify notify);
    #define     gtk_container_children
    GList*      gtk_container_get_children      (GtkContainer *container);
    void        gtk_container_set_reallocate_redraws
                                                (GtkContainer *container,
                                                 gboolean needs_redraws);
    void        gtk_container_set_focus_child   (GtkContainer *container,
                                                 GtkWidget *child);
    GtkAdjustment* gtk_container_get_focus_vadjustment
                                                (GtkContainer *container);
    void        gtk_container_set_focus_vadjustment
                                                (GtkContainer *container,
                                                 GtkAdjustment *adjustment);
    GtkAdjustment* gtk_container_get_focus_hadjustment
                                                (GtkContainer *container);
    void        gtk_container_set_focus_hadjustment
                                                (GtkContainer *container,
                                                 GtkAdjustment *adjustment);
    void        gtk_container_resize_children   (GtkContainer *container);
    GType       gtk_container_child_type        (GtkContainer *container);
    void        gtk_container_child_get         (GtkContainer *container,
                                                 GtkWidget *child,
                                                 const gchar *first_prop_name,
                                                 ...);
    void        gtk_container_child_set         (GtkContainer *container,
                                                 GtkWidget *child,
                                                 const gchar *first_prop_name,
                                                 ...);
    void        gtk_container_child_get_property
                                                (GtkContainer *container,
                                                 GtkWidget *child,
                                                 const gchar *property_name,
                                                 GValue *value);
    void        gtk_container_child_set_property
                                                (GtkContainer *container,
                                                 GtkWidget *child,
                                                 const gchar *property_name,
                                                 const GValue *value);
    void        gtk_container_child_get_valist  (GtkContainer *container,
                                                 GtkWidget *child,
                                                 const gchar *first_property_name,
                                                 va_list var_args);
    void        gtk_container_child_set_valist  (GtkContainer *container,
                                                 GtkWidget *child,
                                                 const gchar *first_property_name,
                                                 va_list var_args);
    void        gtk_container_forall            (GtkContainer *container,
                                                 GtkCallback callback,
                                                 gpointer callback_data);
    guint       gtk_container_get_border_width  (GtkContainer *container);
    void        gtk_container_set_border_width  (GtkContainer *container,
                                                 guint border_width);
    void        gtk_container_propagate_expose  (GtkContainer *container,
                                                 GtkWidget *child,
                                                 GdkEventExpose *event);
    gboolean    gtk_container_get_focus_chain   (GtkContainer *container,
                                                 GList **focusable_widgets);
    void        gtk_container_set_focus_chain   (GtkContainer *container,
                                                 GList *focusable_widgets);
    void        gtk_container_unset_focus_chain (GtkContainer *container);
    GParamSpec* gtk_container_class_find_child_property
                                                (GObjectClass *cclass,
                                                 const gchar *property_name);
    void        gtk_container_class_install_child_property
                                                (GtkContainerClass *cclass,
                                                 guint property_id,
                                                 GParamSpec *pspec);
    GParamSpec** gtk_container_class_list_child_properties
                                                (GObjectClass *cclass,
                                                 guint *n_properties);

## Object Hierarchy

      GObject
       +----GtkObject
             +----GtkWidget
                   +----GtkContainer
                         +----GtkBin
                         +----GtkBox
                         +----GtkCList
                         +----GtkFixed
                         +----GtkPaned
                         +----GtkLayout
                         +----GtkList
                         +----GtkMenuShell
                         +----GtkNotebook
                         +----GtkSocket
                         +----GtkTable
                         +----GtkTextView
                         +----GtkToolbar
                         +----GtkTree
                         +----GtkTreeView

## Implemented Interfaces

GtkContainer implements AtkImplementorIface.

## Properties

      "border-width"         guint                 : Read / Write
      "child"                GtkWidget             : Write
      "resize-mode"          GtkResizeMode         : Read / Write

## Signal Prototypes

    "add"       void        user_function      (GtkContainer *container,
                                                GtkWidget *widget,
                                                gpointer user_data);
    "check-resize"
                void        user_function      (GtkContainer *container,
                                                gpointer user_data);
    "remove"    void        user_function      (GtkContainer *container,
                                                GtkWidget *widget,
                                                gpointer user_data);
    "set-focus-child"
                void        user_function      (GtkContainer *container,
                                                GtkWidget *widget,
                                                gpointer user_data);

## Description

A GTK+ user interface is constructed by nesting widgets inside widgets. Container widgets are the inner nodes in the resulting tree of widgets: they contain other widgets. So, for example, you might have a GtkWindow containing a GtkFrame containing a GtkLabel. If you wanted an image instead of a textual label inside the frame, you might replace the GtkLabel widget with a GtkImage widget.

There are two major kinds of container widgets in GTK+. Both are subclasses of the abstract GtkContainer base class.

The first type of container widget has a single child widget and derives from GtkBin. These containers are decorators, which add some kind of functionality to the child. For example, a GtkButton makes its child into a clickable button; a GtkFrame draws a frame around its child and a GtkWindow places its child widget inside a top-level window.

The second type of container can have more than one child; its purpose is to manage layout. This means that these containers assign sizes and positions to their children. For example, a GtkHBox arranges its children in a horizontal row, and a GtkTable arranges the widgets it contains in a two-dimensional grid.

To fulfill its task, a layout container must negotiate the size requirements with its parent and its children. This negotiation is carried out in two phases, size requisition and size allocation.

### Size Requisition

The size requisition of a widget is it's desired width and height. This is represented by a GtkRequisition.

How a widget determines its desired size depends on the widget. A GtkLabel, for example, requests enough space to display all its text. Container widgets generally base their size request on the requisitions of their children.

The size requisition phase of the widget layout process operates top-down. It starts at a top-level widget, typically a GtkWindow. The top-level widget asks its child for its size requisition by calling `gtk_widget_size_request()`. To determine its requisition, the child asks its own children for their requisitions and so on. Finally, the top-level widget will get a requisition back from its child.

### Size Allocation

When the top-level widget has determined how much space its child would like to have, the second phase of the size negotiation, size allocation, begins. Depending on its configuration (see `gtk_window_set_resizable()`), the top-level widget may be able to expand in order to satisfy the size request or it may have to ignore the size request and keep its fixed size. It then tells its child widget how much space it gets by calling `gtk_widget_size_allocate()`. The child widget divides the space among its children and tells each child how much space it got, and so on. Under normal circumstances, a GtkWindow will always give its child the amount of space the child requested.

A child's size allocation is represented by a GtkAllocation. This struct contains not only a width and height, but also a position (i.e. X and Y coordinates), so that containers can tell their children not only how much space they have gotten, but also where they are positioned inside the space available to the container.

Widgets are required to honor the size allocation they receive; a size request is only a request, and widgets must be able to cope with any size.

### Child properties

GtkContainer introduces child properties - these are object properties that are not specific to either the container or the contained widget, but rather to their relation. Typical examples of child properties are the position or pack-type of a widget which is contained in a GtkBox.

Use `gtk_container_class_install_child_property()` to install child properties for a container class and `gtk_container_class_find_child_property()` or `gtk_container_class_list_child_properties()` to get information about existing child properties.

To set the value of a child property, use `gtk_container_child_set_property()`, `gtk_container_child_set()` or `gtk_container_child_set_valist()`. To obtain the value of a child property, use `gtk_container_child_get_property()`, `gtk_container_child_get()` or `gtk_container_child_get_valist()`. To emit notification about child property changes, use `gtk_widget_child_notify()`.

## Details

### struct GtkContainer

    struct GtkContainer;

### GTK_IS_RESIZE_CONTAINER()

    #define GTK_IS_RESIZE_CONTAINER(widget) (GTK_IS_CONTAINER (widget) && ((GtkContainer*) (widget))->resize_mode != GTK_RESIZE_PARENT)

`widget` : |

### GTK_CONTAINER_WARN_INVALID_CHILD_PROPERTY_ID()

    #define     GTK_CONTAINER_WARN_INVALID_CHILD_PROPERTY_ID(object, property_id, pspec)

`object` : |
`property_id` : |
`pspec` : |

### gtk_container_border_width

    #define	gtk_container_border_width		gtk_container_set_border_width

### Warning

`gtk_container_border_width` is deprecated and should not be used in newly-written code. Use `gtk_container_set_border_width()` instead.

Does the same as `gtk_container_set_border_width()`.

### gtk_container_add ()

    void        gtk_container_add               (GtkContainer *container,
                                                 GtkWidget *widget);

Adds `widget` to `container`. Typically used for simple containers such as GtkWindow, GtkFrame, or GtkButton; for more complicated layout containers such as GtkBox or GtkTable, this function will pick default packing parameters that may not be correct. So consider functions such as `gtk_box_pack_start()` and `gtk_table_attach()` as an alternative to `gtk_container_add()` in those cases. A widget may be added to only one container at a time; you can't place the same widget inside two different containers.

`container` : | a GtkContainer
`widget` : | a widget to be placed inside `container`

### gtk_container_remove ()

    void        gtk_container_remove            (GtkContainer *container,
                                                 GtkWidget *widget);

Removes `widget` from `container`. `widget` must be inside `container`. Note that `container` will own a reference to `widget`, and that this may be the last reference held; so removing a widget from its container can destroy that widget. If you want to use `widget` again, you need to add a reference to it while it's not inside a container, using `g_object_ref()`. If you don't want to use `widget` again it's usually more efficient to simply destroy it directly using `gtk_widget_destroy()` since this will remove it from the container and help break any circular reference count cycles.

`container` : | a GtkContainer
`widget` : | a current child of `container`

### gtk_container_add_with_properties ()

    void        gtk_container_add_with_properties
                                                (GtkContainer *container,
                                                 GtkWidget *widget,
                                                 const gchar *first_prop_name,
                                                 ...);

Adds `widget` to `container`, setting child properties at the same time. See `gtk_container_add()` and `gtk_container_child_set()` for more details.

`container` : | a GtkContainer
`widget` : | a widget to be placed inside `container`
`first_prop_name` : | the name of the first child property to set
`...` : | a `NULL`-terminated list of property names and values, starting with `first_prop_name`.

### gtk_container_get_resize_mode ()

    GtkResizeMode gtk_container_get_resize_mode (GtkContainer *container);

Returns the resize mode for the container. See `gtk_container_set_resize_mode()`.

`container` : | a GtkContainer
Returns : | the current resize mode

### gtk_container_set_resize_mode ()

    void        gtk_container_set_resize_mode   (GtkContainer *container,
                                                 GtkResizeMode resize_mode);

Sets the resize mode for the container.

The resize mode of a container determines whether a resize request will be passed to the container's parent, queued for later execution or executed immediately.

`container` : | a GtkContainer.
`resize_mode` : | the new resize mode.

### gtk_container_check_resize ()

    void        gtk_container_check_resize      (GtkContainer *container);

`container` : |

### gtk_container_foreach ()

    void        gtk_container_foreach           (GtkContainer *container,
                                                 GtkCallback callback,
                                                 gpointer callback_data);

Invokes `callback` on each non-internal child of `container`. See `gtk_container_forall()` for details on what constitutes an "internal" child. Most applications should use `gtk_container_foreach()`, rather than `gtk_container_forall()`.

`container` : | a GtkContainer
`callback` : | a callback
`callback_data` : | callback user data

### gtk_container_foreach_full ()

    void        gtk_container_foreach_full      (GtkContainer *container,
                                                 GtkCallback callback,
                                                 GtkCallbackMarshal marshal,
                                                 gpointer callback_data,
                                                 GtkDestroyNotify notify);

### Warning

`gtk_container_foreach_full` is deprecated and should not be used in newly-written code. Use `gtk_container_foreach()` instead.

`container` : |
`callback` : |
`marshal` : |
`callback_data` : |
`notify` : |

### gtk_container_children

    #define gtk_container_children gtk_container_get_children

### Warning

`gtk_container_children` is deprecated and should not be used in newly-written code. Use `gtk_container_get_children()` instead.

Does the same as `gtk_container_get_children()`.

Returns : |

### gtk_container_get_children ()

    GList*      gtk_container_get_children      (GtkContainer *container);

Returns the the container's non-internal children. See `gtk_container_forall()` for details on what constitutes an "internal" child.

`container` : | a GtkContainer.
Returns : | a newly-allocated list of the container's non-internal children.

### gtk_container_set_reallocate_redraws ()

    void        gtk_container_set_reallocate_redraws
                                                (GtkContainer *container,
                                                 gboolean needs_redraws);

Sets the `reallocate_redraws` flag of the container to the given value.

Containers requesting reallocation redraws get automatically redrawn if any of their children changed allocation.

`container` : | a GtkContainer.
`needs_redraws` : | the new value for the container's `reallocate_redraws` flag.

### gtk_container_set_focus_child ()

    void        gtk_container_set_focus_child   (GtkContainer *container,
                                                 GtkWidget *child);

`container` : |
`child` : |

### gtk_container_get_focus_vadjustment ()

    GtkAdjustment* gtk_container_get_focus_vadjustment
                                                (GtkContainer *container);

Retrieves the vertical focus adjustment for the container. See `gtk_container_set_focus_vadjustment()`.

`container` : | a GtkContainer
Returns : | the vertical focus adjustment, or `NULL` if none has been set.

### gtk_container_set_focus_vadjustment ()

    void        gtk_container_set_focus_vadjustment
                                                (GtkContainer *container,
                                                 GtkAdjustment *adjustment);

Hooks up an adjustment to focus handling in a container, so when a child of the container is focused, the adjustment is scrolled to show that widget. This function sets the vertical alignment. See `gtk_scrolled_window_get_vadjustment()` for a typical way of obtaining the adjustment and `gtk_container_set_focus_hadjustment()` for setting the horizontal adjustment.

The adjustments have to be in pixel units and in the same coordinate system as the allocation for immediate children of the container.

`container` : | a GtkContainer
`adjustment` : | an adjustment which should be adjusted when the focus is moved among the descendents of `container`

### gtk_container_get_focus_hadjustment ()

    GtkAdjustment* gtk_container_get_focus_hadjustment
                                                (GtkContainer *container);

Retrieves the horizontal focus adjustment for the container. See `gtk_container_set_focus_hadjustment()`.

`container` : | a GtkContainer
Returns : | the horizontal focus adjustment, or `NULL` if none has been set.

### gtk_container_set_focus_hadjustment ()

    void        gtk_container_set_focus_hadjustment
                                                (GtkContainer *container,
                                                 GtkAdjustment *adjustment);

Hooks up an adjustment to focus handling in a container, so when a child of the container is focused, the adjustment is scrolled to show that widget. This function sets the horizontal alignment. See `gtk_scrolled_window_get_hadjustment()` for a typical way of obtaining the adjustment and `gtk_container_set_focus_vadjustment()` for setting the vertical adjustment.

The adjustments have to be in pixel units and in the same coordinate system as the allocation for immediate children of the container.

`container` : | a GtkContainer
`adjustment` : | an adjustment which should be adjusted when the focus is moved among the descendents of `container`

### gtk_container_resize_children ()

    void        gtk_container_resize_children   (GtkContainer *container);

`container` : |

### gtk_container_child_type ()

    GType       gtk_container_child_type        (GtkContainer *container);

Returns the type of the children supported by the container.

Note that this may return `G_TYPE_NONE` to indicate that no more children can be added, e.g. for a GtkPaned which already has two children.

`container` : | a GtkContainer.
Returns : | a GType.

### gtk_container_child_get ()

    void        gtk_container_child_get         (GtkContainer *container,
                                                 GtkWidget *child,
                                                 const gchar *first_prop_name,
                                                 ...);

Gets the values of one or more child properties for `child` and `container`.

`container` : | a GtkContainer
`child` : | a widget which is a child of `container`
`first_prop_name` : | the name of the first property to get
`...` : | a `NULL`-terminated list of property names and GValue*, starting with `first_prop_name`.

### gtk_container_child_set ()

    void        gtk_container_child_set         (GtkContainer *container,
                                                 GtkWidget *child,
                                                 const gchar *first_prop_name,
                                                 ...);

Sets one or more child properties for `child` and `container`.

`container` : | a GtkContainer
`child` : | a widget which is a child of `container`
`first_prop_name` : | the name of the first property to set
`...` : | a `NULL`-terminated list of property names and values, starting with `first_prop_name`.

### gtk_container_child_get_property ()

    void        gtk_container_child_get_property
                                                (GtkContainer *container,
                                                 GtkWidget *child,
                                                 const gchar *property_name,
                                                 GValue *value);

Gets the value of a child property for `child` and `container`.

`container` : | a GtkContainer
`child` : | a widget which is a child of `container`
`property_name` : | the name of the property to get
`value` : | a location to return the value

### gtk_container_child_set_property ()

    void        gtk_container_child_set_property
                                                (GtkContainer *container,
                                                 GtkWidget *child,
                                                 const gchar *property_name,
                                                 const GValue *value);

Sets a child property for `child` and `container`.

`container` : | a GtkContainer
`child` : | a widget which is a child of `container`
`property_name` : | the name of the property to set
`value` : | the value to set the property to

### gtk_container_child_get_valist ()

    void        gtk_container_child_get_valist  (GtkContainer *container,
                                                 GtkWidget *child,
                                                 const gchar *first_property_name,
                                                 va_list var_args);

Gets the values of one or more child properties for `child` and `container`.

`container` : | a GtkContainer
`child` : | a widget which is a child of `container`
`first_property_name` : | the name of the first property to get
`var_args` : | a `NULL`-terminated list of property names and GValue*, starting with `first_prop_name`.

### gtk_container_child_set_valist ()

    void        gtk_container_child_set_valist  (GtkContainer *container,
                                                 GtkWidget *child,
                                                 const gchar *first_property_name,
                                                 va_list var_args);

Sets one or more child properties for `child` and `container`.

`container` : | a GtkContainer
`child` : | a widget which is a child of `container`
`first_property_name` : | the name of the first property to set
`var_args` : | a `NULL`-terminated list of property names and values, starting with `first_prop_name`.

### gtk_container_forall ()

    void        gtk_container_forall            (GtkContainer *container,
                                                 GtkCallback callback,
                                                 gpointer callback_data);

Invokes `callback` on each child of `container`, including children that are considered "internal" (implementation details of the container). "Internal" children generally weren't added by the user of the container, but were added by the container implementation itself. Most applications should use `gtk_container_foreach()`, rather than `gtk_container_forall()`.

`container` : | a GtkContainer
`callback` : | a callback
`callback_data` : | callback user data

### gtk_container_get_border_width ()

    guint       gtk_container_get_border_width  (GtkContainer *container);

Retrieves the border width of the container. See `gtk_container_set_border_width()`.

`container` : | a GtkContainer
Returns : | the current border width

### gtk_container_set_border_width ()

    void        gtk_container_set_border_width  (GtkContainer *container,
                                                 guint border_width);

Sets the border width of the container.

The border width of a container is the amount of space to leave around the outside of the container. The only exception to this is GtkWindow; because toplevel windows can't leave space outside, they leave the space inside. The border is added on all sides of the container. To add space to only one side, one approach is to create a GtkAlignment widget, call `gtk_widget_set_usize()` to give it a size, and place it on the side of the container as a spacer.

`container` : | a GtkContainer
`border_width` : | amount of blank space to leave outside the container. Valid values are in the range 0-65535 pixels.

### gtk_container_propagate_expose ()

    void        gtk_container_propagate_expose  (GtkContainer *container,
                                                 GtkWidget *child,
                                                 GdkEventExpose *event);

When a container receives an expose event, it must send synthetic expose events to all children that don't have their own GdkWindows. This function provides a convenient way of doing this. A container, when it receives an expose event, calls `gtk_container_propagate_expose()` once for each child, passing in the event the container received.

`gtk_container_propagate_expose()` takes care of deciding whether an expose event needs to be sent to the child, intersecting the event's area with the child area, and sending the event.

In most cases, a container can simply either simply inherit the ::expose implementation from GtkContainer, or, do some drawing and then chain to the ::expose implementation from GtkContainer.

`container` : | a GtkContainer
`child` : | a child of `container`
`event` : | a expose event sent to container

### gtk_container_get_focus_chain ()

    gboolean    gtk_container_get_focus_chain   (GtkContainer *container,
                                                 GList **focusable_widgets);

Retrieves the focus chain of the container, if one has been set explicitly. If no focus chain has been explicitly set, GTK+ computes the focus chain based on the positions of the children. In that case, GTK+ stores `NULL` in `focusable_widgets` and returns `FALSE`.

`container` : | a GtkContainer
`focusable_widgets` : | location to store the focus chain of the container, or `NULL`. You should free this list using `g_list_free()` when you are done with it, however no additional reference count is added to the individual widgets in the focus chain.
Returns : | `TRUE` if the focus chain of the container has been set explicitly.

### gtk_container_set_focus_chain ()

    void        gtk_container_set_focus_chain   (GtkContainer *container,
                                                 GList *focusable_widgets);

Sets a focus chain, overriding the one computed automatically by GTK+.

In principle each widget in the chain should be a descendant of the container, but this is not enforced by this method, since it's allowed to set the focus chain before you pack the widgets, or have a widget in the chain that isn't always packed. The necessary checks are done when the focus chain is actually traversed.

`container` : | a GtkContainer.
`focusable_widgets` : | the new focus chain.

### gtk_container_unset_focus_chain ()

    void        gtk_container_unset_focus_chain (GtkContainer *container);

Removes a focus chain explicitly set with `gtk_container_set_focus_chain()`.

`container` : | a GtkContainer.

### gtk_container_class_find_child_property ()

    GParamSpec* gtk_container_class_find_child_property
                                                (GObjectClass *cclass,
                                                 const gchar *property_name);

Finds a child property of a container class by name.

`cclass` : | a GtkContainerClass
`property_name` : | the name of the child property to find
Returns : | the GParamSpec of the child property or `NULL` if `class` has no child property with that name.

### gtk_container_class_install_child_property ()

    void        gtk_container_class_install_child_property
                                                (GtkContainerClass *cclass,
                                                 guint property_id,
                                                 GParamSpec *pspec);

Installs a child property on a container class.

`cclass` : | a GtkContainerClass
`property_id` : | the id for the property
`pspec` : | the GParamSpec for the property

### gtk_container_class_list_child_properties ()

    GParamSpec** gtk_container_class_list_child_properties
                                                (GObjectClass *cclass,
                                                 guint *n_properties);

Returns all child properties of a container class.

`cclass` : | a GtkContainerClass
`n_properties` : | location to return the number of child properties found
Returns : | a newly allocated array of GParamSpec*. The array must be freed with `g_free()`.

## Properties

### The "`border-width`" property

      "border-width"         guint                 : Read / Write

The width of the empty border outside the containers children.

Allowed values: <= G_MAXINT

Default value: 0

### The "`child`" property

      "child"                GtkWidget             : Write

Can be used to add a new child to the container.

### The "`resize-mode`" property

      "resize-mode"          GtkResizeMode         : Read / Write

Specify how resize events are handled.

Default value: GTK_RESIZE_PARENT

## Signals

### The "add" signal

    void        user_function                  (GtkContainer *container,
                                                GtkWidget *widget,
                                                gpointer user_data);

`container` : | the object which received the signal.
`widget` : |
`user_data` : | user data set when the signal handler was connected.

### The "check-resize" signal

    void        user_function                  (GtkContainer *container,
                                                gpointer user_data);

`container` : | the object which received the signal.
`user_data` : | user data set when the signal handler was connected.

### The "remove" signal

    void        user_function                  (GtkContainer *container,
                                                GtkWidget *widget,
                                                gpointer user_data);

`container` : | the object which received the signal.
`widget` : |
`user_data` : | user data set when the signal handler was connected.

### The "set-focus-child" signal

    void        user_function                  (GtkContainer *container,
                                                GtkWidget *widget,
                                                gpointer user_data);

`container` : | the object which received the signal.
`widget` : |
`user_data` : | user data set when the signal handler was connected.