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RemoveLogicalChild Method

FrameworkElement.RemoveLogicalChild Method

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.

Namespace:  System.Windows
Assembly:  PresentationFramework (in PresentationFramework.dll)

protected internal void RemoveLogicalChild(
	Object child
)

Parameters

child
Type: System.Object

The element to remove.

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.

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();
        }
    }
}

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1
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