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Class Gtk.CellArea

Import line: Gtk =;
GIR File: Gtk-3.0.gir
C documentation: GtkCellArea
Class : CellArea
Implements: Gtk.Buildable, Gtk.CellLayout
Extends: GObject.InitiallyUnowned
The GtkCellArea is an abstract class for GtkCellLayout widgets
(also referred to as "layouting widgets") to interface with an
arbitrary number of GtkCellRenderers and interact with the user
for a given GtkTreeModel row.
The cell area handles events, focus navigation, drawing and
size requests and allocations for a given row of data.
Usually users dont have to interact with the GtkCellArea directly
unless they are implementing a cell-layouting widget themselves.

Requesting area sizes

As outlined in GtkWidget's
geometry management section, GTK+ uses a height-for-width
geometry management system to compute the sizes of widgets and user
interfaces. GtkCellArea uses the same semantics to calculate the
size of an area for an arbitrary number of GtkTreeModel rows.
When requesting the size of a cell area one needs to calculate
the size for a handful of rows, and this will be done differently by
different layouting widgets. For instance a GtkTreeViewColumn
always lines up the areas from top to bottom while a GtkIconView
on the other hand might enforce that all areas received the same
width and wrap the areas around, requesting height for more cell
areas when allocated less width.
It's also important for areas to maintain some cell
alignments with areas rendered for adjacent rows (cells can
appear "columnized" inside an area even when the size of
cells are different in each row). For this reason the GtkCellArea
uses a GtkCellAreaContext object to store the alignments
and sizes along the way (as well as the overall largest minimum
and natural size for all the rows which have been calculated
with the said context).
The GtkCellAreaContext is an opaque object specific to the
GtkCellArea which created it (see gtk_cell_area_create_context()).
The owning cell-layouting widget can create as many contexts as
it wishes to calculate sizes of rows which should receive the
same size in at least one orientation (horizontally or vertically),
However, it's important that the same GtkCellAreaContext which
was used to request the sizes for a given GtkTreeModel row be
used when rendering or processing events for that row.
In order to request the width of all the rows at the root level
of a GtkTreeModel one would do the following:

Requesting the width of a handful of GtkTreeModel rows

GtkTreeIter iter;
gint minimum_width;
gint natural_width;
valid = gtk_tree_model_get_iter_first (model, &iter);
while (valid)
gtk_cell_area_apply_attributes (area, model, &iter, FALSE, FALSE);
gtk_cell_area_get_preferred_width (area, context, widget, NULL, NULL);
valid = gtk_tree_model_iter_next (model, &iter);
gtk_cell_area_context_get_preferred_width (context, &minimum_width, &natural_width);

Note that in this example it's not important to observe the
returned minimum and natural width of the area for each row
unless the cell-layouting object is actually interested in the
widths of individual rows. The overall width is however stored
in the accompanying GtkCellAreaContext object and can be consulted
at any time.
This can be useful since GtkCellLayout widgets usually have to
support requesting and rendering rows in treemodels with an
exceedingly large amount of rows. The GtkCellLayout widget in
that case would calculate the required width of the rows in an
idle or timeout source (see g_timeout_add()) and when the widget
is requested its actual width in GtkWidgetClass.get_preferred_width()
it can simply consult the width accumulated so far in the
GtkCellAreaContext object.
A simple example where rows are rendered from top to bottom and
take up the full width of the layouting widget would look like:

A typical get_preferred_width() implementation

static void
foo_get_preferred_width (GtkWidget *widget,
gint *minimum_size,
gint *natural_size)
Foo *foo = FOO (widget);
FooPrivate *priv = foo->priv;
foo_ensure_at_least_one_handfull_of_rows_have_been_requested (foo);
gtk_cell_area_context_get_preferred_width (priv->context, minimum_size, natural_size);

In the above example the Foo widget has to make sure that some
row sizes have been calculated (the amount of rows that Foo judged
was appropriate to request space for in a single timeout iteration)
before simply returning the amount of space required by the area via
the GtkCellAreaContext.
Requesting the height for width (or width for height) of an area is
a similar task except in this case the GtkCellAreaContext does not
store the data (actually, it does not know how much space the layouting
widget plans to allocate it for every row. It's up to the layouting
widget to render each row of data with the appropriate height and
width which was requested by the GtkCellArea).
In order to request the height for width of all the rows at the
root level of a GtkTreeModel one would do the following:

Requesting the height for width of a handful of GtkTreeModel rows

GtkTreeIter iter;
gint minimum_height;
gint natural_height;
gint full_minimum_height = 0;
gint full_natural_height = 0;
valid = gtk_tree_model_get_iter_first (model, &iter);
while (valid)
gtk_cell_area_apply_attributes (area, model, &iter, FALSE, FALSE);
gtk_cell_area_get_preferred_height_for_width (area, context, widget,
width, &minimum_height, &natural_height);
if (width_is_for_allocation)
cache_row_height (&iter, minimum_height, natural_height);
full_minimum_height += minimum_height;
full_natural_height += natural_height;
valid = gtk_tree_model_iter_next (model, &iter);

Note that in the above example we would need to cache the heights
returned for each row so that we would know what sizes to render the
areas for each row. However we would only want to really cache the
heights if the request is intended for the layouting widgets real
In some cases the layouting widget is requested the height for an
arbitrary for_width, this is a special case for layouting widgets
who need to request size for tens of thousands of rows. For this
case it's only important that the layouting widget calculate
one reasonably sized chunk of rows and return that height
synchronously. The reasoning here is that any layouting widget is
at least capable of synchronously calculating enough height to fill
the screen height (or scrolled window height) in response to a single
call to GtkWidgetClass.get_preferred_height_for_width(). Returning
a perfect height for width that is larger than the screen area is
inconsequential since after the layouting receives an allocation
from a scrolled window it simply continues to drive the the scrollbar
values while more and more height is required for the row heights
that are calculated in the background.

Rendering Areas

Once area sizes have been aquired at least for the rows in the
visible area of the layouting widget they can be rendered at
GtkWidgetClass.draw() time.
A crude example of how to render all the rows at the root level
runs as follows:

Requesting the width of a handful of GtkTreeModel rows

GtkAllocation allocation;
GdkRectangle cell_area = { 0, };
GtkTreeIter iter;
gint minimum_width;
gint natural_width;
gtk_widget_get_allocation (widget, &allocation);
cell_area.width = allocation.width;
valid = gtk_tree_model_get_iter_first (model, &iter);
while (valid)
cell_area.height = get_cached_height_for_row (&iter);
gtk_cell_area_apply_attributes (area, model, &iter, FALSE, FALSE);
gtk_cell_area_render (area, context, widget, cr,
&cell_area, &cell_area, state_flags, FALSE);
cell_area.y += cell_area.height;
valid = gtk_tree_model_iter_next (model, &iter);

Note that the cached height in this example really depends on how
the layouting widget works. The layouting widget might decide to
give every row its minimum or natural height or, if the model content
is expected to fit inside the layouting widget without scrolling, it
would make sense to calculate the allocation for each row at
GtkWidget::size-allocate time using gtk_distribute_natural_allocation().

Handling Events and Driving Keyboard Focus

Passing events to the area is as simple as handling events on any
normal widget and then passing them to the gtk_cell_area_event()
API as they come in. Usually GtkCellArea is only interested in
button events, however some customized derived areas can be implemented
who are interested in handling other events. Handling an event can
trigger the GtkCellArea::focus-changed signal to fire; as well as
GtkCellArea::add-editable in the case that an editable cell was
clicked and needs to start editing. You can call
gtk_cell_area_stop_editing() at any time to cancel any cell editing
that is currently in progress.
The GtkCellArea drives keyboard focus from cell to cell in a way
similar to GtkWidget. For layouting widgets that support giving
focus to cells it's important to remember to pass GTK_CELL_RENDERER_FOCUSED
to the area functions for the row that has focus and to tell the
area to paint the focus at render time.
Layouting widgets that accept focus on cells should implement the
GtkWidgetClass.focus() virtual method. The layouting widget is always
responsible for knowing where GtkTreeModel rows are rendered inside
the widget, so at GtkWidgetClass.focus() time the layouting widget
should use the GtkCellArea methods to navigate focus inside the area
and then observe the GtkDirectionType to pass the focus to adjacent
rows and areas.
A basic example of how the GtkWidgetClass.focus() virtual method
should be implemented:

Implementing keyboard focus navigation

static gboolean
foo_focus (GtkWidget *widget,
GtkDirectionType direction)
Foo *foo = FOO (widget);
FooPrivate *priv = foo->priv;
gint focus_row;
gboolean have_focus = FALSE;
focus_row = priv->focus_row;
if (!gtk_widget_has_focus (widget))
gtk_widget_grab_focus (widget);
valid = gtk_tree_model_iter_nth_child (priv->model, &iter, NULL, priv->focus_row);
while (valid)
gtk_cell_area_apply_attributes (priv->area, priv->model, &iter, FALSE, FALSE);
if (gtk_cell_area_focus (priv->area, direction))
priv->focus_row = focus_row;
have_focus = TRUE;
if (direction == GTK_DIR_RIGHT ||
direction == GTK_DIR_LEFT)
else if (direction == GTK_DIR_UP ||
direction == GTK_DIR_TAB_BACKWARD)
if (focus_row == 0)
valid = gtk_tree_model_iter_nth_child (priv->model, &iter, NULL, focus_row);
if (focus_row == last_row)
valid = gtk_tree_model_iter_next (priv->model, &iter);
return have_focus;

Note that the layouting widget is responsible for matching the
GtkDirectionType values to the way it lays out its cells.

Cell Properties

The GtkCellArea introduces cell properties
for GtkCellRenderers in very much the same way that GtkContainer
introduces child properties
for GtkWidgets. This provides some general interfaces for defining
the relationship cell areas have with their cells. For instance in a
GtkCellAreaBox a cell might "expand" and receive extra space when
the area is allocated more than its full natural request, or a cell
might be configured to "align" with adjacent rows which were requested
and rendered with the same GtkCellAreaContext.
Use gtk_cell_area_class_install_cell_property() to install cell
properties for a cell area class and gtk_cell_area_class_find_cell_property()
or gtk_cell_area_class_list_cell_properties() to get information about
existing cell properties.
To set the value of a cell property, use gtk_cell_area_cell_set_property(),
gtk_cell_area_cell_set() or gtk_cell_area_cell_set_valist(). To obtain
the value of a cell property, use gtk_cell_area_cell_get_property(),
gtk_cell_area_cell_get() or gtk_cell_area_cell_get_valist().

Properties Defined By
Methods / Constructors
Method / Constructor Defined By
Events - usage syntax: this.signals.EVENTNAME.connect( Function )
Event Defined By
Used by These Methods / Signals / Properties
Class / Namespace Method / Signal / Properties
area : Gtk.CellArea
The GtkCellArea this context was created by
get_area () : Gtk.CellArea
Fetches the GtkCellArea this context was created by.
get_area () : Gtk.CellArea
Returns the underlying GtkCellArea which might be cell_layout
if called on a GtkCellArea or might be NULL if no GtkCellArea
is used by cell_layout.
cell_area : Gtk.CellArea
The GtkCellArea rendering cells
If no area is specified when creating the cell view with gtk_cell_view_new_with_context()
a horizontally oriented GtkCellAreaBox will be used.
new Gtk.CellView.with_context (CellArea area, CellAreaContext context) : Gtk.Widget
Create a new Gtk.CellView
cell_area : Gtk.CellArea
The GtkCellArea used to layout cell renderers for this combo box.
new Gtk.ComboBox.with_area (CellArea area) : Gtk.Widget
Create a new Gtk.ComboBox
new Gtk.ComboBox.with_area_and_entry (CellArea area) : Gtk.Widget
Create a new Gtk.ComboBox
cell_area : Gtk.CellArea
The GtkCellArea used to layout cell renderers in the treeview column.
new Gtk.EntryCompletion.with_area (CellArea area) : Gtk.EntryCompletion
Create a new Gtk.EntryCompletion
cell_area : Gtk.CellArea
The GtkCellArea used to layout cell renderers for this view.
new Gtk.IconView.with_area (CellArea area) : Gtk.Widget
Create a new Gtk.IconView
cell_area : Gtk.CellArea
The GtkCellArea used to layout cell renderers for this column.
new Gtk.TreeViewColumn.with_area (CellArea area) : Gtk.TreeViewColumn
Create a new Gtk.TreeViewColumn
Documentation generated by Introspection Doc Generator Loosely Based on JsDoc Toolkit on Sat Apr 16 2011 17:12:12 GMT+0800 (HKT)