Adds the provided object to the logical tree of this element.
Assembly: PresentationFramework (in PresentationFramework.dll)
Use this method for the implementation of collections on objects that represent logical child elements of an element. Collection maintenance for child element collections might be done in property getters or setters, class handling of Changed events, constructors, or within the collection types themselves.
For control authors, manipulating the logical tree at this level is not the recommended practice, unless none of the content models for available base control classes are appropriate for your control scenario. Consider subclassing at the level of ContentControl, ItemsControl, and HeaderedItemsControl. These classes provide a content model with particular enforcement of logical tree child elements through dedicated APIs, as well as support for other features typically desirable in a WPF control such as styling through templates. For more information on how to use LogicalChildren and , see Trees in WPF.
may throw an exception if called at a time when the logical tree is being iterated by another process.
The following example implements a Child property on a custom FrameworkElement that does its own visual layer implementation. The property setter is designed so that if the value changes, the old value is removed from the logical tree, as well as a class-specific visual collection. The property value is cached, and then the new value is added to both the logical tree and the custom visual collection.
<System.ComponentModel.DefaultValue(GetType(Object), Nothing)> Public Overridable Property Child() As UIElement Get Return _child End Get Set(ByVal value As UIElement) If _child IsNot value Then 'need to remove old element from logical tree If _child IsNot Nothing Then OnDetachChild(_child) RemoveLogicalChild(_child) End If _vc.Clear() If value IsNot Nothing Then 'add to visual _vc.Add(value) 'add to logical AddLogicalChild(value) End If 'always add the overlay child back into the visual tree if its set If _overlayVisual IsNot Nothing Then _vc.Add(_overlayVisual) End If 'cache the new child _child = value 'notify derived types of the new child If value IsNot Nothing Then OnAttachChild(_child) End If InvalidateMeasure() End If End Set End Property
Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.