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 #GtkGrid arranges the widgets it contains
in a two-dimensional grid.
For implementations of #GtkContainer the virtual method #GtkContainerClass.forall()
is always required, since it's used for drawing and other internal operations
on the children.
If the #GtkContainer implementation expect to have non internal children
it's needed to implement both #GtkContainerClass.add() and #GtkContainerClass.remove().
If the GtkContainer implementation has internal children, they should be added
with gtk.widget.Widget.setParent on init() and removed with gtk.widget.Widget.unparent
in the #GtkWidgetClass.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
#GtkSizeRequestMode that is gtk.types.SizeRequestMode.HeightForWidth or
gtk.types.SizeRequestMode.WidthForHeight. 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.Widget.getPreferredWidth and then through gtk.widget.Widget.getPreferredHeightForWidth.
When handling requests in the opposite #GtkSizeRequestMode it is important that
every widget request at least enough space to display all of its content at all times.
When gtk.widget.Widget.getPreferredHeight 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 as follows:
staticvoid
foo_container_get_preferred_height (GtkWidget *widget,
gint *min_height,
gint *nat_height)
{
if (i_am_in_height_for_width_mode)
{
gint min_width;
GTK_WIDGET_GET_CLASS (widget)->get_preferred_width (widget,
&min_width,
NULL);
GTK_WIDGET_GET_CLASS (widget)->get_preferred_height_for_width
(widget,
min_width,
min_height,
nat_height);
}
else
{
... many containers support both request modes, execute the
real width-for-height request here by returning the
collective heights of all widgets that are stacked
vertically (or whatever is appropriate forthis container)
...
}
}
Similarly, when gtk.widget.Widget.getPreferredWidthForHeight is called for a container or widget
that is height-for-width, it then only needs to return the base minimum width like so:
staticvoid
foo_container_get_preferred_width_for_height (GtkWidget *widget,
gint for_height,
gint *min_width,
gint *nat_width)
{
if (i_am_in_height_for_width_mode)
{
GTK_WIDGET_GET_CLASS (widget)->get_preferred_width (widget,
min_width,
nat_width);
}
else
{
... execute the real width-for-height request here based on
the required width of the children collectively if the
container were to be allocated the said height ...
}
}
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.Widget.getPreferredWidth for each of its children.
For each potential group of children that are lined up horizontally, the values returned by
gtk.widget.Widget.getPreferredWidth should be collected in an array of #GtkRequestedSize structures.
Any child spacing should be removed from the input @for_width and then the collective size should be
allocated using the gtk.global.distributeNaturalAllocation convenience function.
The container will then move on to request the preferred height for each child by using
gtk.widget.Widget.getPreferredHeightForWidth and using the sizes stored in the #GtkRequestedSize 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 #GtkRequestedSize array and gtk.global.distributeNaturalAllocation 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
#GtkRequestedSize 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.global.distributeNaturalAllocation
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 [GtkWidget’s geometry management section][geometry-management]
to learn more about implementing height-for-width geometry management for widgets.
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.
The GtkContainer implementation of the GtkBuildable interface supports
a <packing> element for children, which can contain multiple <property>
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 used
for regular properties.
Since 3.16, containers can have a <focus-chain> element containing multiple
<widget> elements, one for each child that should be added to the focus
chain. The ”name” attribute gives the id of the widget.
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 #GtkGrid arranges the widgets it contains in a two-dimensional grid.
For implementations of #GtkContainer the virtual method #GtkContainerClass.forall() is always required, since it's used for drawing and other internal operations on the children. If the #GtkContainer implementation expect to have non internal children it's needed to implement both #GtkContainerClass.add() and #GtkContainerClass.remove(). If the GtkContainer implementation has internal children, they should be added with gtk.widget.Widget.setParent on init() and removed with gtk.widget.Widget.unparent in the #GtkWidgetClass.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 #GtkSizeRequestMode that is gtk.types.SizeRequestMode.HeightForWidth or gtk.types.SizeRequestMode.WidthForHeight. 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.Widget.getPreferredWidth and then through gtk.widget.Widget.getPreferredHeightForWidth. When handling requests in the opposite #GtkSizeRequestMode it is important that every widget request at least enough space to display all of its content at all times.
When gtk.widget.Widget.getPreferredHeight 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 as follows:
Similarly, when gtk.widget.Widget.getPreferredWidthForHeight is called for a container or widget that is height-for-width, it then only needs to return the base minimum width like so:
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.Widget.getPreferredWidth for each of its children.
For each potential group of children that are lined up horizontally, the values returned by gtk.widget.Widget.getPreferredWidth should be collected in an array of #GtkRequestedSize structures. Any child spacing should be removed from the input @for_width and then the collective size should be allocated using the gtk.global.distributeNaturalAllocation convenience function.
The container will then move on to request the preferred height for each child by using gtk.widget.Widget.getPreferredHeightForWidth and using the sizes stored in the #GtkRequestedSize 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 #GtkRequestedSize array and gtk.global.distributeNaturalAllocation 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 #GtkRequestedSize 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.global.distributeNaturalAllocation 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 [GtkWidget’s geometry management section][geometry-management] to learn more about implementing height-for-width geometry management for widgets.
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.ContainerClass.installChildProperty to install child properties for a container class and gtk.container_class.ContainerClass.findChildProperty or gtk.container_class.ContainerClass.listChildProperties to get information about existing child properties.
To set the value of a child property, use gtk.container.Container.childSetProperty, gtk.container.Container.childSet or gtk.container.Container.childSetValist. To obtain the value of a child property, use gtk.container.Container.childGetProperty, gtk.container.Container.childGet or gtk.container.Container.childGetValist. To emit notification about child property changes, use gtk.widget.Widget.childNotify.
GtkContainer as GtkBuildable
The GtkContainer implementation of the GtkBuildable interface supports a <packing> element for children, which can contain multiple <property> 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 used for regular properties.
Since 3.16, containers can have a <focus-chain> element containing multiple <widget> 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: