## GtkCellLayout GtkCellLayout — An interface for packing cells |

## Synopsis

    #include <gtk/gtk.h>

                        GtkCellLayout;
    struct              GtkCellLayoutIface;
    void                (*GtkCellLayoutDataFunc)            (GtkCellLayout *cell_layout,
                                                             GtkCellRenderer *cell,
                                                             GtkTreeModel *tree_model,
                                                             GtkTreeIter *iter,
                                                             gpointer data);
    void                gtk_cell_layout_pack_start          (GtkCellLayout *cell_layout,
                                                             GtkCellRenderer *cell,
                                                             gboolean expand);
    void                gtk_cell_layout_pack_end            (GtkCellLayout *cell_layout,
                                                             GtkCellRenderer *cell,
                                                             gboolean expand);
    GtkCellArea *       gtk_cell_layout_get_area            (GtkCellLayout *cell_layout);
    GList *             gtk_cell_layout_get_cells           (GtkCellLayout *cell_layout);
    void                gtk_cell_layout_reorder             (GtkCellLayout *cell_layout,
                                                             GtkCellRenderer *cell,
                                                             gint position);
    void                gtk_cell_layout_clear               (GtkCellLayout *cell_layout);
    void                gtk_cell_layout_set_attributes      (GtkCellLayout *cell_layout,
                                                             GtkCellRenderer *cell,
                                                             ...);
    void                gtk_cell_layout_add_attribute       (GtkCellLayout *cell_layout,
                                                             GtkCellRenderer *cell,
                                                             const gchar *attribute,
                                                             gint column);
    void                gtk_cell_layout_set_cell_data_func  (GtkCellLayout *cell_layout,
                                                             GtkCellRenderer *cell,
                                                             GtkCellLayoutDataFunc func,
                                                             gpointer func_data,
                                                             GDestroyNotify destroy);
    void                gtk_cell_layout_clear_attributes    (GtkCellLayout *cell_layout,
                                                             GtkCellRenderer *cell);

## Object Hierarchy

      GInterface
       +----GtkCellLayout

## Prerequisites

GtkCellLayout requires GObject.

## Known Implementations

GtkCellLayout is implemented by GtkAppChooserButton, GtkCellArea, GtkCellAreaBox, GtkCellView, GtkComboBox, GtkComboBoxText, GtkEntryCompletion, GtkIconView and GtkTreeViewColumn.

## Description

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, GtkComboBoxEntry, 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.

Example 64. A UI definition fragment specifying attributes

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    <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 GtkCellLayouts 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 defined in the normal way.

Example 65. A UI definition fragment specifying cell properties

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    <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

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    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).

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    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.

## Details

### GtkCellLayout

    typedef struct _GtkCellLayout GtkCellLayout;

### struct GtkCellLayoutIface

    struct GtkCellLayoutIface {
      GTypeInterface g_iface;

      /* Virtual Table */
      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 gchar           *attribute,
                                   gint                   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,
                                   gint                   position);
      GList* (* get_cells)        (GtkCellLayout         *cell_layout);

      GtkCellArea *(* get_area)   (GtkCellLayout         *cell_layout);
    };

### GtkCellLayoutDataFunc ()

    void                (*GtkCellLayoutDataFunc)            (GtkCellLayout *cell_layout,
                                                             GtkCellRenderer *cell,
                                                             GtkTreeModel *tree_model,
                                                             GtkTreeIter *iter,
                                                             gpointer data);

A function which should set the value of `cell_layout`'s cell renderer(s) as appropriate.

`cell_layout` : | a GtkCellLayout
`cell` : | the cell renderer whose value is to be set
`tree_model` : | the model
`iter` : | a GtkTreeIter indicating the row to set the value for
`data` : | user data passed to `gtk_cell_layout_set_cell_data_func()`

### gtk_cell_layout_pack_start ()

    void                gtk_cell_layout_pack_start          (GtkCellLayout *cell_layout,
                                                             GtkCellRenderer *cell,
                                                             gboolean expand);

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`.

Note that reusing the same cell renderer is not supported.

`cell_layout` : | a GtkCellLayout
`cell` : | a GtkCellRenderer
`expand` : | `TRUE` if `cell` is to be given extra space allocated to `cell_layout`

Since 2.4

### gtk_cell_layout_pack_end ()

    void                gtk_cell_layout_pack_end            (GtkCellLayout *cell_layout,
                                                             GtkCellRenderer *cell,
                                                             gboolean expand);

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`.

Note that reusing the same cell renderer is not supported.

`cell_layout` : | a GtkCellLayout
`cell` : | a GtkCellRenderer
`expand` : | `TRUE` if `cell` is to be given extra space allocated to `cell_layout`

Since 2.4

### gtk_cell_layout_get_area ()

    GtkCellArea *       gtk_cell_layout_get_area            (GtkCellLayout *cell_layout);

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_layout` : | a GtkCellLayout
Returns : | the cell area used by `cell_layout`. [transfer none]

Since 3.0

### gtk_cell_layout_get_cells ()

    GList *             gtk_cell_layout_get_cells           (GtkCellLayout *cell_layout);

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

`cell_layout` : | a GtkCellLayout
Returns : | a list of cell renderers. The list, but not the renderers has been newly allocated and should be freed with `g_list_free()` when no longer needed. [element-type GtkCellRenderer][transfer container]

Since 2.12

### gtk_cell_layout_reorder ()

    void                gtk_cell_layout_reorder             (GtkCellLayout *cell_layout,
                                                             GtkCellRenderer *cell,
                                                             gint position);

Re-inserts `cell` at `position`.

Note that `cell` has already to be packed into `cell_layout` for this to function properly.

`cell_layout` : | a GtkCellLayout
`cell` : | a GtkCellRenderer to reorder
`position` : | new position to insert `cell` at

Since 2.4

### gtk_cell_layout_clear ()

    void                gtk_cell_layout_clear               (GtkCellLayout *cell_layout);

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

`cell_layout` : | a GtkCellLayout

Since 2.4

### gtk_cell_layout_set_attributes ()

    void                gtk_cell_layout_set_attributes      (GtkCellLayout *cell_layout,
                                                             GtkCellRenderer *cell,
                                                             ...);

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

The attributes should be in attribute/column order, as in `gtk_cell_layout_add_attribute()`. All existing attributes are removed, and replaced with the new attributes.

`cell_layout` : | a GtkCellLayout
`cell` : | a GtkCellRenderer
`...` : | a `NULL`-terminated list of attributes

Since 2.4

### gtk_cell_layout_add_attribute ()

    void                gtk_cell_layout_add_attribute       (GtkCellLayout *cell_layout,
                                                             GtkCellRenderer *cell,
                                                             const gchar *attribute,
                                                             gint column);

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

The `column` is the column of the model to get a value from, and the `attribute` is the parameter on `cell` to be set from the value. So for example if column 2 of the model contains strings, you could have the "text" attribute of a GtkCellRendererText get its values from column 2.

`cell_layout` : | a GtkCellLayout
`cell` : | a GtkCellRenderer
`attribute` : | an attribute on the renderer
`column` : | the column position on the model to get the attribute from

Since 2.4

### gtk_cell_layout_set_cell_data_func ()

    void                gtk_cell_layout_set_cell_data_func  (GtkCellLayout *cell_layout,
                                                             GtkCellRenderer *cell,
                                                             GtkCellLayoutDataFunc func,
                                                             gpointer func_data,
                                                             GDestroyNotify destroy);

Sets the GtkCellLayoutDataFunc to use for `cell_layout`.

This function is used instead of the standard attributes mapping for setting the column value, and should set the value of `cell_layout`'s cell renderer(s) as appropriate.

`func` may be `NULL` to remove a previously set function.

`cell_layout` : | a GtkCellLayout
`cell` : | a GtkCellRenderer
`func` : | the GtkCellLayoutDataFunc to use, or `NULL`. [allow-none]
`func_data` : | user data for `func`
`destroy` : | destroy notify for `func_data`

Since 2.4

### gtk_cell_layout_clear_attributes ()

    void                gtk_cell_layout_clear_attributes    (GtkCellLayout *cell_layout,
                                                             GtkCellRenderer *cell);

Clears all existing attributes previously set with `gtk_cell_layout_set_attributes()`.

`cell_layout` : | a GtkCellLayout
`cell` : | a GtkCellRenderer to clear the attribute mapping on

Since 2.4