The FrameworkElement implementation of VisualChildrenCount always returns either zero or one. Classes that maintain a visual child collection that might exceed one must override both this property and GetVisualChild.

This property is generally used to determine the upper bounds of the current child collection for purposes of implementing the layout overrides (MeasureOverride, ArrangeOverride).

If your class supports more than one visual child in a child element collection, override this property to return the count of elements in that collection. You must do this even if the collection object itself returns a count. Element layout logic at the WPF framework level presumes that all elements will return a valid count through their VisualChildrenCount property.

The following example shows how a custom adorner uses the values declared by a VisualCollection that it maintains for its multiple visual children and reports these values through overrides of VisualChildrenCount and GetVisualChild.

    ' To store and manage the adorner's visual children.
    Private visualChildren As VisualCollection


...


    ' Override the VisualChildrenCount and GetVisualChild properties to interface with 
    ' the adorner's visual collection.
    Protected Overrides ReadOnly Property VisualChildrenCount() As Integer
        Get
            Return visualChildren.Count
        End Get
    End Property
    Protected Overrides Function GetVisualChild(ByVal index As Integer) As Visual
        Return visualChildren(index)
    End Function

// To store and manage the adorner's visual children.
VisualCollection visualChildren;


...


// Override the VisualChildrenCount and GetVisualChild properties to interface with 
// the adorner's visual collection.
protected override int VisualChildrenCount { get { return visualChildren.Count; } }
protected override Visual GetVisualChild(int index) { return visualChildren[index]; }

.NET Framework

.NET Framework Client Profile

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

Reference

Other Resources