แก้ไข

แชร์ผ่าน

FrameworkElement.RemoveLogicalChild(Object) Method

  • Reference

Definition

Namespace:
System.Windows
Assembly:
PresentationFramework.dll

Removes the provided object from this element's logical tree. FrameworkElement updates the affected logical tree parent pointers to keep in sync with this deletion.

protected public:
 void RemoveLogicalChild(System::Object ^ child);
protected internal void RemoveLogicalChild (object child);
member this.RemoveLogicalChild : obj -> unit
Protected Friend Sub RemoveLogicalChild (child As Object)

Parameters

child
Object

The element to remove.

Examples

The following example implements a Child property on a custom FrameworkElement that does its own visual layer implementation. The property's 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 values are cached, and then the new value is added to both the standard WPF framework level logical tree and the custom visual collection.

public virtual UIElement Child
{
    get
    {
        return _child;
    }
    set
    {
        if (_child != value)
        {
            //need to remove old element from logical tree
            if (_child != null)
            {
                OnDetachChild(_child);
                RemoveLogicalChild(_child);
            }

            _vc.Clear();

            if (value != null)
            {
                //add to visual
                _vc.Add(value);
                //add to logical
                AddLogicalChild(value);
            }

            //always add the overlay child back into the visual tree if its set
            if (_overlayVisual != null)
                _vc.Add(_overlayVisual);

            //cache the new child
            _child = value;

            //notify derived types of the new child
            if (value != null)
                OnAttachChild(_child);

            InvalidateMeasure();
        }
    }
}

<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

Remarks

Use this method for the implementation of collections on objects that represent logical children of an element. This might be done in property getters or setters, class handlers 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 provided base control class' content models are appropriate. Consider subclassing at the level of ContentControl, ItemsControl, and HeaderedItemsControl. These classes provide a content model with particular enforcement of logical children through dedicated APIs, as well as support for other features typically desirable in a WPF control such as styling through templates.

Applies to

See also