Gtk.CellLayout
Description: Reference for Gtk.CellLayout

### Interface

# GtkCellLayout

#### Description [src]

    interface Gtk.CellLayout : GObject.Object

An interface for packing cells

`GtkCellLayout` is an interface to be implemented by all objects which want to provide a `GtkTreeViewColumn` like API for packing cells, setting attributes and data funcs.

One of the notable features provided by implementations of `GtkCellLayout` 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 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 `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 GtkCellLayout which also implement the GtkBuildable interface (`GtkCellView`, `GtkIconView`, `GtkComboBox`, `GtkEntryCompletion`, `GtkTreeViewColumn`) accept `GtkCellRenderer` 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.

This is an example of a UI definition fragment specifying attributes:

    <object class="GtkCellView">
      <child>
        <object class="GtkCellRendererText"/>
        <attributes>
          <attribute name="text">0</attribute>
        </attributes>
      </child>
    </object>

Furthermore for implementations of `GtkCellLayout` that use a `GtkCellArea` to lay out cells (all `GtkCellLayout`s in GTK use a `GtkCellArea`) cell properties can also be defined in the format by specifying the custom `<cell-packing>` attribute which can contain multiple `<property>` elements.

Here is a UI definition fragment specifying cell properties:

    <object class="GtkTreeViewColumn">
      <child>
        <object class="GtkCellRendererText"/>
        <cell-packing>
          <property name="align">True</property>
          <property name="expand">False</property>
        </cell-packing>
      </child>
    </object>

# Subclassing GtkCellLayout implementations

When subclassing a widget that implements `GtkCellLayout` like `GtkIconView` or `GtkComboBox`, there are some considerations related to the fact that these widgets internally use a `GtkCellArea`. The cell area is exposed as a construct-only property by these widgets. This means that it is possible to e.g. do

    GtkWIdget *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.

#### Prerequisite

In order to implement CellLayout, your type must inherit from `GObject`.

#### Implementations

- GtkCellArea
- GtkCellAreaBox
- GtkCellView
- GtkComboBox
- GtkComboBoxText
- GtkEntryCompletion
- GtkIconView
- GtkTreeViewColumn

#### Instance methods

###### gtk_cell_layout_add_attribute

Adds an attribute mapping to the list in `cell_layout`.

###### gtk_cell_layout_clear

Unsets all the mappings on all renderers on `cell_layout` and removes all renderers from `cell_layout`.

###### gtk_cell_layout_clear_attributes

Clears all existing attributes previously set with gtk_cell_layout_set_attributes().

###### gtk_cell_layout_get_area

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`.

###### gtk_cell_layout_get_cells

Returns the cell renderers which have been added to `cell_layout`.

###### gtk_cell_layout_pack_end

Adds the `cell` to the end of `cell_layout`. If `expand` is `FALSE`, then the `cell` is allocated no more space than it needs. Any unused space is divided evenly between cells for which `expand` is `TRUE`.

###### gtk_cell_layout_pack_start

Packs the `cell` into the beginning of `cell_layout`. If `expand` is `FALSE`, then the `cell` is allocated no more space than it needs. Any unused space is divided evenly between cells for which `expand` is `TRUE`.

###### gtk_cell_layout_reorder

Re-inserts `cell` at `position`.

###### gtk_cell_layout_set_attributes

Sets the attributes in the parameter list as the attributes of `cell_layout`.

###### gtk_cell_layout_set_cell_data_func

Sets the `GtkCellLayout`DataFunc to use for `cell_layout`.

#### Interface structure

    struct GtkCellLayoutIface {
      void (* pack_start) (
        GtkCellLayout* cell_layout,
        GtkCellRenderer* cell,
        gboolean expand
      );
      void (* pack_end) (
        GtkCellLayout* cell_layout,
        GtkCellRenderer* cell,
        gboolean expand
      );
      void (* clear) (
        GtkCellLayout* cell_layout
      );
      void (* add_attribute) (
        GtkCellLayout* cell_layout,
        GtkCellRenderer* cell,
        const char* attribute,
        int column
      );
      void (* set_cell_data_func) (
        GtkCellLayout* cell_layout,
        GtkCellRenderer* cell,
        GtkCellLayoutDataFunc func,
        gpointer func_data,
        GDestroyNotify destroy
      );
      void (* clear_attributes) (
        GtkCellLayout* cell_layout,
        GtkCellRenderer* cell
      );
      void (* reorder) (
        GtkCellLayout* cell_layout,
        GtkCellRenderer* cell,
        int position
      );
      GList* (* get_cells) (
        GtkCellLayout* cell_layout
      );
      GtkCellArea* (* get_area) (
        GtkCellLayout* cell_layout
      );

    }

###### Interface members

`pack_start` |
    void (* pack_start) (
        GtkCellLayout* cell_layout,
        GtkCellRenderer* cell,
        gboolean expand
      )
| No description available.
`pack_end` |
    void (* pack_end) (
        GtkCellLayout* cell_layout,
        GtkCellRenderer* cell,
        gboolean expand
      )
| No description available.
`clear` |
    void (* clear) (
        GtkCellLayout* cell_layout
      )
| No description available.
`add_attribute` |
    void (* add_attribute) (
        GtkCellLayout* cell_layout,
        GtkCellRenderer* cell,
        const char* attribute,
        int column
      )
| No description available.
`set_cell_data_func` |
    void (* set_cell_data_func) (
        GtkCellLayout* cell_layout,
        GtkCellRenderer* cell,
        GtkCellLayoutDataFunc func,
        gpointer func_data,
        GDestroyNotify destroy
      )
| No description available.
`clear_attributes` |
    void (* clear_attributes) (
        GtkCellLayout* cell_layout,
        GtkCellRenderer* cell
      )
| No description available.
`reorder` |
    void (* reorder) (
        GtkCellLayout* cell_layout,
        GtkCellRenderer* cell,
        int position
      )
| No description available.
`get_cells` |
    GList* (* get_cells) (
        GtkCellLayout* cell_layout
      )
| No description available.
`get_area` |
    GtkCellArea* (* get_area) (
        GtkCellLayout* cell_layout
      )
| No description available.

#### Virtual methods

###### Gtk.CellLayout.add_attribute

Adds an attribute mapping to the list in `cell_layout`.

###### Gtk.CellLayout.clear

Unsets all the mappings on all renderers on `cell_layout` and removes all renderers from `cell_layout`.

###### Gtk.CellLayout.clear_attributes

Clears all existing attributes previously set with gtk_cell_layout_set_attributes().

###### Gtk.CellLayout.get_area

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`.

###### Gtk.CellLayout.get_cells

Returns the cell renderers which have been added to `cell_layout`.

###### Gtk.CellLayout.pack_end

Adds the `cell` to the end of `cell_layout`. If `expand` is `FALSE`, then the `cell` is allocated no more space than it needs. Any unused space is divided evenly between cells for which `expand` is `TRUE`.

###### Gtk.CellLayout.pack_start

Packs the `cell` into the beginning of `cell_layout`. If `expand` is `FALSE`, then the `cell` is allocated no more space than it needs. Any unused space is divided evenly between cells for which `expand` is `TRUE`.

###### Gtk.CellLayout.reorder

Re-inserts `cell` at `position`.

###### Gtk.CellLayout.set_cell_data_func

Sets the `GtkCellLayout`DataFunc to use for `cell_layout`.