Package: gtk

Class gtk-cell-layout


g-object, common-lisp:standard-object, common-lisp:t

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gtk-cell-layout is an interface to be implemented by all objects which want to provide a gtk-tree-view-column-like API for packing cells, setting attributes and data funcs.

One of the notable features provided by implementations of gtk-cell-layout are attributes. Attributes let you set the properties in flexible ways. They can just be set to constant values like regular properties. But they can also be mapped to a column of the underlying tree model with the function gtk-cell-layout-set-attributes, which means that the value of the attribute can change from cell to cell as they are rendered by the cell renderer. Finally, it is possible to specify a function with the function gtk-cell-layout-set-cell-data-func that is called to determine the value of the attribute for each cell that is rendered.

GtkCellLayouts as GtkBuildable
Implementations of gtk-cell-layout which also implement the gtk-buildable interface (gtk-cell-view, gtk-icon-view, gtk-combo-box, gtk-combo-box-entry, gtk-entry-completion, gtk-tree-view-column) accept gtk-cell-renderer objects as <child> elements in UI definitions. They support a custom <attributes> element for their children, which can contain multiple <attribute> elements. Each <attribute> element has a name attribute which specifies a property of the cell renderer; the content of the element is the attribute value.

Example: A UI definition fragment specifying attributes
 <object class="GtkCellView">
     <object class="GtkCellRendererText"/>
       <attribute name="text">0</attribute>
Furthermore for implementations of gtk-cell-layout that use a gtk-cell-area to lay out cells (all gtk-cell-layout's in GTK+ use a gtk-cell-area) cell properties can also be defined in the format by specifying the custom <cell-packing> attribute which can contain multiple <property> elements defined in the normal way.

Example: A UI definition fragment specifying cell properties
 <object class="GtkTreeViewColumn">
     <object class="GtkCellRendererText"/>
       <property name="align">True</property>
       <property name="expand">False</property>
Subclassing GtkCellLayout implementations
When subclassing a widget that implements gtk-cell-layout like gtk-icon-view or gtk-combo-box, there are some considerations related to the fact that these widgets internally use a gtk-cell-area. The cell area is exposed as a construct-only property by these widgets. This means that it is possible to e. g. do
 combo = g_object_new (GTK_TYPE_COMBO_BOX,
                       "cell-area", my_cell_area, NULL);    
to use a custom cell area with a combo box. But construct properties are only initialized after instance init() functions have run, which means that using functions which rely on the existence of the cell area in your subclass' init() function will cause the default cell area to be instantiated. In this case, a provided construct property value will be ignored (with a warning, to alert you to the problem).
 static void
 my_combo_box_init (MyComboBox *b)
   GtkCellRenderer *cell;

cell = gtk_cell_renderer_pixbuf_new (); /* The following call causes the default cell area for combo boxes, * a GtkCellAreaBox, to be instantiated */ gtk_cell_layout_pack_start (GTK_CELL_LAYOUT (b), cell, FALSE); ... } GtkWidget * my_combo_box_new (GtkCellArea *area) { /* This call is going to cause a warning * about area being ignored */ return g_object_new (MY_TYPE_COMBO_BOX, "cell-area", area, NULL); }
If supporting alternative cell areas with your derived widget is not important, then this does not have to concern you. If you want to support alternative cell areas, you can do so by moving the problematic calls out of init() and into a constructor() for your class.

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