module Gtk::CellLayout

Overview

An interface for packing cells

Gtk::CellLayout is an interface to be implemented by all objects which want to provide a Gtk::TreeViewColumn like API for packing cells, setting attributes and data funcs.

One of the notable features provided by implementations of Gtk::CellLayout 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.

Gtk::CellLayouts as Gtk::Buildable

Implementations of Gtk::CellLayout which also implement the Gtk::Buildable interface (Gtk::CellView, Gtk::IconView, Gtk::ComboBox, Gtk::EntryCompletion, Gtk::TreeViewColumn) accept Gtk::CellRenderer 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:

WARNING ⚠️ The following code is in xml ⚠️

<object class="Gtk::CellView">
  <child>
    <object class="Gtk::CellRendererText"/>
    <attributes>
      <attribute name="text">0</attribute>
    </attributes>
  </child>
</object>

Furthermore for implementations of Gtk::CellLayout that use a Gtk::CellArea to lay out cells (all Gtk::CellLayouts in GTK use a Gtk::CellArea) 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:

WARNING ⚠️ The following code is in xml ⚠️

<object class="Gtk::TreeViewColumn">
  <child>
    <object class="Gtk::CellRendererText"/>
    <cell-packing>
      <property name="align">True</property>
      <property name="expand">False</property>
    </cell-packing>
  </child>
</object>

Subclassing Gtk::CellLayout implementations

When subclassing a widget that implements Gtk::CellLayout like Gtk::IconView or Gtk::ComboBox, there are some considerations related to the fact that these widgets internally use a Gtk::CellArea. The cell area is exposed as a construct-only property by these widgets. This means that it is possible to e.g. do

WARNING ⚠️ The following code is in c ⚠️

Gtk::WIdget *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).

WARNING ⚠️ The following code is in c ⚠️

static void
my_combo_box_init (MyComboBox *b)
{
  Gtk::CellRenderer *cell;

  cell = gtk_cell_renderer_pixbuf_new ();

  // The following call causes the default cell area for combo boxes,
  // a Gtk::CellAreaBox, to be instantiated
  gtk_cell_layout_pack_start (GTK_CELL_LAYOUT (b), cell, FALSE);
  ...
}

Gtk::Widget *
my_combo_box_new (Gtk::CellArea *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.

Direct including types

Defined in:

lib/gi-crystal/src/auto/gtk-4.0/cell_layout.cr

Class Method Summary

Instance Method Summary

Class Method Detail

def self.g_type : UInt64 #

Instance Method Detail

def add_attribute(cell : Gtk::CellRenderer, attribute : String, column : Int32) : Nil #

def area : Gtk::CellArea? #

def cells : GLib::List #

def clear : Nil #

def clear_attributes(cell : Gtk::CellRenderer) : Nil #

def pack_end(cell : Gtk::CellRenderer, expand : Bool) : Nil #

def pack_start(cell : Gtk::CellRenderer, expand : Bool) : Nil #

def reorder(cell : Gtk::CellRenderer, position : Int32) : Nil #

def set_cell_data_func(cell : Gtk::CellRenderer, func : Gtk::CellLayoutDataFunc?) : Nil #

abstract def to_unsafe #