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Visual.AddVisualChild(Visual) Method

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Definition

Namespace:
System.Windows.Media
Assembly:
PresentationCore.dll

Defines the parent-child relationship between two visuals.

protected:
 void AddVisualChild(System::Windows::Media::Visual ^ child);
protected void AddVisualChild (System.Windows.Media.Visual child);
member this.AddVisualChild : System.Windows.Media.Visual -> unit
Protected Sub AddVisualChild (child As Visual)

Parameters

child
Visual

The child visual object to add to parent visual.

Examples

The following example shows how to define custom storage requirements for a visual child. The example uses the AddVisualChild and RemoveVisualChild methods to sets up the parent-child relationship between the parent visual and child. In order for the visual tree to be enumerated correctly, the example provides overridden implementations of the GetVisualChild method and VisualChildrenCount property.

Note

Although it is possible to use VisualCollection to create parent-child relationships between visual objects, it is more efficient to provide your own custom storage implementation when only one child is linked to a parent.

// Create a host visual derived from the FrameworkElement class.
// This class provides layout, event handling, and container support for
// the child visual object.
public class MyVisualHost : FrameworkElement
{
    private DrawingVisual _child;

    public MyVisualHost(DrawingVisual drawingVisual)
    {
        _child = drawingVisual;
        this.AddVisualChild(_child);
    }

    public DrawingVisual Child
    {
        get
        {
            return _child;
        }

        set
        {
            if (_child != value)
            {
                this.RemoveVisualChild(_child);
                _child = value;
                this.AddVisualChild(_child);
            }
        }
    }

    // Provide a required override for the VisualChildrenCount property.
    protected override int VisualChildrenCount
    {
        get { return _child == null ? 0 : 1; }
    }

    // Provide a required override for the GetVisualChild method.
    protected override Visual GetVisualChild(int index)
    {
        if (_child == null)
        {
            throw new ArgumentOutOfRangeException();
        }

        return _child;
    }

' Create a host visual derived from the FrameworkElement class.
' This class provides layout, event handling, and container support for
' the child visual object.
Public Class MyVisualHost
    Inherits FrameworkElement
    Private _child As DrawingVisual

    Public Sub New(ByVal drawingVisual As DrawingVisual)
        _child = drawingVisual
        Me.AddVisualChild(_child)
    End Sub

    Public Property Child() As DrawingVisual
        Get
            Return _child
        End Get

        Set(ByVal value As DrawingVisual)
            If _child IsNot value Then
                Me.RemoveVisualChild(_child)
                _child = value
                Me.AddVisualChild(_child)
            End If
        End Set
    End Property

    ' Provide a required override for the VisualChildrenCount property.
    Protected Overrides ReadOnly Property VisualChildrenCount() As Integer
        Get
            Return If(_child Is Nothing, 0, 1)
        End Get
    End Property

    ' Provide a required override for the GetVisualChild method.
    Protected Overrides Function GetVisualChild(ByVal index As Integer) As Visual
        If _child Is Nothing Then
            Throw New ArgumentOutOfRangeException()
        End If

        Return _child
    End Function

Remarks

The AddVisualChild method sets up the parent-child relationship between two visual objects. This method must be used when you need greater low-level control over the underlying storage implementation of visual child objects. VisualCollection can be used as a default implementation for storing child objects.

Applies to

See also