Programming WPF, 2nd Edition

Decorator

System.Object
    System.Windows.Threading.DispatcherObject
        System.Windows.DependencyObject
            System.Windows.Media.Visual
                System.Windows.UIElement
                    System.Windows.FrameworkElement
                        System.Windows.Controls.Decorator

Decorator is the base class for elements that contain a single child, and which either apply some kind of effect or offer a service. For example, Border adds an outline and optional padding around an element. ViewBox scales its child to fit the space available. InkPresenter enables ink rendering on its child.

Tip

Despite being defined in the System.Windows.Controls namespace, a Decorator is not technically a control, as it does not derive from the Control class. Indeed, many of the types in the System.Windows.Controls namespace are not controls. This namespace contains many utility types typically used in conjunction with controls in order to build a user interface.

Decorator is a very simple class—it just defines a public Child element and performs the necessary work to ensure that the child is added to the logical and visual trees. Its layout implementation simply defers to the child element. You should use either this or ContentControl when writing a custom element that wraps a single child. See the ContentControl section, later in this appendix, for a discussion on how to choose between these two types.