Interfacing Raku to Gnome GTK+

Gnome::Gtk3::Container

Base class for widgets which contain other widgets

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 Gnome::Gtk3::Window containing a Gnome::Gtk3::Frame containing a Gnome::Gtk3::Label. If you wanted an image instead of a textual label inside the frame, you might replace the Gnome::Gtk3::Label widget with a Gnome::Gtk3::Image widget.

There are two major kinds of container widgets in GTK+. Both are subclasses of the abstract Gnome::Gtk3::Container base class.

The first type of container widget has a single child widget and derives from Gnome::Gtk3::Bin. These containers are decorators, which add some kind of functionality to the child. For example, a Gnome::Gtk3::Button makes its child into a clickable button; a Gnome::Gtk3::Frame draws a frame around its child and a Gnome::Gtk3::Window 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 Gnome::Gtk3::HBox arranges its children in a horizontal row, and a Gnome::Gtk3::Grid arranges the widgets it contains in a two-dimensional grid.

For implementations of Gnome::Gtk3::Container the virtual method Gnome::Gtk3::ContainerClass.forall() is always required, since it’s used for drawing and other internal operations on the children. If the Gnome::Gtk3::Container implementation expect to have non internal children it’s needed to implement both Gnome::Gtk3::ContainerClass.add() and Gnome::Gtk3::ContainerClass.remove(). If the Gnome::Gtk3::Container implementation has internal children, they should be added with gtk_widget_set_parent() on init() and removed with gtk_widget_unparent() in the Gnome::Gtk3::WidgetClass.destroy() implementation. See more about implementing custom widgets at https://wiki.gnome.org/HowDoI/CustomWidgets

Height for width geometry management

GTK+ uses a height-for-width (and width-for-height) geometry management system. Height-for-width means that a widget can change how much vertical space it needs, depending on the amount of horizontal space that it is given (and similar for width-for-height).

There are some things to keep in mind when implementing container widgets that make use of GTK+’s height for width geometry management system. First, it’s important to note that a container must prioritize one of its dimensions, that is to say that a widget or container can only have a Gnome::Gtk3::SizeRequestMode that is GTK_SIZE_REQUEST_HEIGHT_FOR_WIDTH or GTK_SIZE_REQUEST_WIDTH_FOR_HEIGHT. However, every widget and container must be able to respond to the APIs for both dimensions, i.e. even if a widget has a request mode that is height-for-width, it is possible that its parent will request its sizes using the width-for-height APIs.

To ensure that everything works properly, here are some guidelines to follow when implementing height-for-width (or width-for-height) containers.

Each request mode involves 2 virtual methods. Height-for-width apis run through gtk_widget_get_preferred_width() and then through gtk_widget_get_preferred_height_for_width(). When handling requests in the opposite Gnome::Gtk3::SizeRequestMode it is important that every widget request at least enough space to display all of its content at all times.

When gtk_widget_get_preferred_height() is called on a container that is height-for-width, the container must return the height for its minimum width. This is easily achieved by simply calling the reverse apis implemented for itself.

Similarly, when gtk_widget_get_preferred_width_for_height() is called for a container or widget that is height-for-width, it then only needs to return the base minimum width

Height for width requests are generally implemented in terms of a virtual allocation of widgets in the input orientation. Assuming an height-for-width request mode, a container would implement the get_preferred_height_for_width() virtual function by first calling gtk_widget_get_preferred_width() for each of its children.

For each potential group of children that are lined up horizontally, the values returned by gtk_widget_get_preferred_width() should be collected in an array of Gnome::Gtk3::RequestedSize structures. Any child spacing should be removed from the input for_width and then the collective size should be allocated using the gtk_distribute_natural_allocation() convenience function.

The container will then move on to request the preferred height for each child by using gtk_widget_get_preferred_height_for_width() and using the sizes stored in the Gnome::Gtk3::RequestedSize array.

To allocate a height-for-width container, it’s again important to consider that a container must prioritize one dimension over the other. So if a container is a height-for-width container it must first allocate all widgets horizontally using a Gnome::Gtk3::RequestedSize array and gtk_distribute_natural_allocation() and then add any extra space (if and where appropriate) for the widget to expand.

After adding all the expand space, the container assumes it was allocated sufficient height to fit all of its content. At this time, the container must use the total horizontal sizes of each widget to request the height-for-width of each of its children and store the requests in a Gnome::Gtk3::RequestedSize array for any widgets that stack vertically (for tabular containers this can be generalized into the heights and widths of rows and columns). The vertical space must then again be distributed using gtk_distribute_natural_allocation() while this time considering the allocated height of the widget minus any vertical spacing that the container adds. Then vertical expand space should be added where appropriate and available and the container should go on to actually allocating the child widgets.

See Gnome::Gtk3::Widget’s geometry management section to learn more about implementing height-for-width geometry management for widgets.

Gnome::Gtk3::Container as Gnome::Gtk3::Buildable

The Gnome::Gtk3::Container implementation of the Gnome::Gtk3::Buildable interface supports a element for children, which can contain multiple elements that specify child properties for the child.

Since 2.16, child properties can also be marked as translatable using the same “translatable”, “comments” and “context” attributes that are usedfor regular properties.

Since 3.16, containers can have a element containing multiple elements, one for each child that should be added to the focus chain. The ”name” attribute gives the id of the widget.

An example of these properties in UI definitions:

<object class="GtkBox>">
  <child>
    <object class="GtkEntry>" id="entry1"/>
    <packing>
      <property name="pack-type">start</property>
    </packing>
  </child>
  <child>
    <object class="GtkEntry>" id="entry2"/>
  </child>
  <focus-chain>
    <widget name="entry1"/>
    <widget name="entry2"/>
  </focus-chain>
</object>

Synopsis

Declaration

unit class Gnome::Gtk3::Container;
also is Gnome::Gtk3::Widget;

Uml Diagram

Methods

new

multi method new ( N-GObject :$native-object! )

Create an object using a native object from elsewhere. See also Gnome::GObject::Object.

multi method new ( Str :$build-id! )

Create an object using a native object from a builder. See also Gnome::GObject::Object.

add

Adds $widget to this container. Typically used for simple containers such as Gnome::Gtk3::Window, Gnome::Gtk3::Frame, or Gnome::Gtk3::Button; for more complicated layout containers such as Gnome::Gtk3::Box or Gnome::Gtk3::Grid, this function will pick default packing parameters that may not be correct. So consider functions such as Gnome::Gtk3::Box.pack-start() and Gnome::Gtk3::Grid.attach() as an alternative to 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.

Note that some containers, such as Gnome::Gtk3::ScrolledWindow or Gnome::Gtk3::ListBox, may add intermediate children between the added widget and the container.

method add ( N-GObject() $widget )
  • $widget; a widget to be placed inside this container

foreach

Invokes a callback method on each non-internal child of this container. See forall() for details on what constitutes an “internal” child. For all practical purposes, this function should iterate over precisely those child widgets that were added to the container by the application with explicit add() calls.

Most applications should use foreach(), rather than forall().

method foreach (
  Any:D $callback-object, Str:D $callback-name, *%user-options
)

  • $callback-object; An object where the callback method is defined

  • $callback-name; method name of the callback. A name ending in -rk gets a raku widget instead of a native object.

  • %user-options; A list of named arguments which are provided to the callback. A special named argumend, :give-raku-objects, is used to provide raku objects instead of the native objects in the same way the extension -rk would do. This might be a better way because one can check the named argument if a raku object is provided or not, see examples below.

Example

An example from the t/Container.t test program where both methods are used;

class X {
  method cb2 ( Gnome::Gtk3::Label() $rk, :$label ) {
    is $rk.get-name, 'GtkLabel', '.foreach(): cb2()';
    is $rk.get-text, $label, 'label text';
  }

  method cb3 ( N-GObject $o, Str :$label ) {
    is $o.().get-name, 'GtkLabel', '.foreach(): cb3()';
    is $o.().get-text, $label, 'label text';
  }
}

$b .= new(:label<some-text>);
$b.foreach( X.new, 'cb2', :label<some-text>);
$b.foreach( X.new, 'cb3', :label<some-text>);

get-border-width

Retrieves the border width of the container. See set-border-width().

Returns: the current border width

method get-border-width ( --> UInt )

get-children, get-children-rk

Returns the container’s non-internal children. See forall() for details on what constitutes an “internal” child.

Returns: a newly-allocated list of the container’s non-internal children.

method get-children ( --> N-GList )
method get-children-rk ( --> Gnome::Glib::List )

get-focus-child

Returns the current focus child widget inside this container. This is not the currently focused widget. That can be obtained by calling Gnome::Gtk3::Window.get-focus().

Returns: The child widget which will receive the focus inside this container when the this container is focused, or undefined if none is set.

method get-focus-child ( --> N-GObject )

get-focus-hadjustment

Retrieves the horizontal focus adjustment for the container. See set-focus-hadjustment().

Returns: the horizontal focus adjustment, or undefined if none has been set. In the -rk case, an invalid Widget is returned. It is a native object for Gnome::Gtk3::Adjustment.

method get-focus-hadjustment ( --> N-GObject )

get-focus-vadjustment

Retrieves the vertical focus adjustment for the container. See set-focus-vadjustment().

Returns: the vertical focus adjustment, or undefined if none has been set. It is a native object for Gnome::Gtk3::Adjustment.

method get-focus-vadjustment ( --> N-GObject )

get-path-for-child

Returns a newly created widget path representing all the widget hierarchy from the toplevel down to and including child.

Returns: A native object for Gnome::Gtk3::WidgetPath

method get-path-for-child ( N-GObject() $child --> N-GObject )
  • $child; a child of this container

propagate-draw

When a container receives a call to the draw function, it must send synthetic draw calls to all children that don’t have their own Gnome::Gtk3::Windows. This function provides a convenient way of doing this. A container, when it receives a call to its draw function, calls propagate-draw() once for each child, passing in the cr the container received.

gtk-container-propagate-draw() takes care of translating the origin of cr, and deciding whether the draw needs to be sent to the child. It is a convenient and optimized way of getting the same effect as calling gtk-widget-draw() on the child directly.

In most cases, a container can simply either inherit the draw implementation from Gnome::Gtk3::Container, or do some drawing and then chain to the draw implementation from Gnome::Gtk3::Container.

method propagate-draw ( N-GObject() $child, cairo_t $cr )

  • $child; a child of this container

  • $cr; Cairo context as passed to the container. If you want to use cr in container’s draw function, consider using cairo-save() and cairo-restore() before calling this function.

remove

Removes widget from this container. widget must be inside this container. Note that this 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 before removing it from 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.

method remove ( N-GObject() $widget )
  • $widget; a current child of this container

set-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 Gnome::Gtk3::Window; 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, use a specific margin property on the child widget, for example margin-top.

method set-border-width ( UInt $border_width )
  • $border_width; amount of blank space to leave outside the container. Valid values are in the range 0-65535 pixels.

set-focus-child

Sets, or unsets if child is undefined, the focused child of this container.

This function emits the GtkContainer::set-focus-child signal of this container. Implementations of Gnome::Gtk3::Container can override the default behaviour by overriding the class closure of this signal.

This is function is mostly meant to be used by widgets. Applications can use gtk-widget-grab-focus() to manually set the focus to a specific widget.

method set-focus-child ( N-GObject() $child )
  • $child; a Gnome::Gtk3::Widget, or undefined

set-focus-hadjustment

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 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.

method set-focus-hadjustment ( N-GObject() $adjustment )
  • $adjustment; an adjustment which should be adjusted when the focus is moved among the descendents of this container

set-focus-vadjustment

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 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.

method set-focus-vadjustment ( N-GObject() $adjustment )
  • $adjustment; an adjustment which should be adjusted when the focus is moved among the descendents of this container

Signals

add

method handler (
  N-GObject #`{ native widget } $n-widget,
  Gnome::Gtk3::Container :_widget($container),
  Int :$_handler-id,
  N-GObject :$_native-object,
  *%user-options
)

  • $n-widget; the added widget

  • $container; The instance which registered the signal

  • $_handler-id; The handler id which is returned from the registration

  • $_native-object; The native object provided by the caller wrapped in the Raku object.

  • %user-options; A list of named arguments provided at the register-signal() method

check-resize

method handler (
  Gnome::Gtk3::Container :_widget($container),
  Int :$_handler-id,
  N-GObject :$_native-object,
  *%user-options
)

  • $container; The instance which registered the signal

  • $_handler-id; The handler id which is returned from the registration

  • $_native-object; The native object provided by the caller wrapped in the Raku object.

  • %user-options; A list of named arguments provided at the register-signal() method

remove

method handler (
  N-GObject #`{ native widget } $n-widget,
  Gnome::Gtk3::Container :_widget($container),
  Int :$_handler-id,
  N-GObject :$_native-object,
  *%user-options
)

  • $n-widget; The removed widget

  • $container; The instance which registered the signal

  • $_handler-id; The handler id which is returned from the registration

  • $_native-object; The native object provided by the caller wrapped in the Raku object.

  • %user-options; A list of named arguments provided at the register-signal() method

set-focus-child

method handler (
  N-GObject #`{ native widget } $widget,
  Gnome::Gtk3::Container :_widget($container),
  Int :$_handler-id,
  N-GObject :$_native-object,
  *%user-options
)

  • $widget; The focussed child

  • $container; The instance which registered the signal

  • $_handler-id; The handler id which is returned from the registration

  • $_native-object; The native object provided by the caller wrapped in the Raku object.

  • %user-options; A list of named arguments provided at the register-signal() method

Properties

border-width

The width of the empty border outside the containers children

  • Gnome::GObject::Value type of this property is G_TYPE_UINT

  • Parameter is readable and writable.

  • Minimum value is 0.

  • Maximum value is 65535.

  • Default value is 0.