HitTestResultCallback Delegate
Represents a callback that is used to customize hit testing. WPF invokes the HitTestResultCallback to report hit test intersections to the user.
Assembly: PresentationCore (in PresentationCore.dll)
'Declaration Public Delegate Function HitTestResultCallback ( _ result As HitTestResult _ ) As HitTestResultBehavior
Parameters
- result
- Type: System.Windows.Media.HitTestResult
The HitTestResult value that represents a visual object that is returned from a hit test.
Return Value
Type: System.Windows.Media.HitTestResultBehaviorA HitTestFilterBehavior that represents the action resulting from the hit test.
The hit test callback method defines the actions that you perform when a hit test is identified on a particular visual object in the visual tree. After you perform the actions, your callback is expected to return a HitTestResultBehavior value that determines whether to continue iterating through the visual tree for any other visual objects.
The following example shows how to invoke HitTest by using a HitTestResultCallback value. The corresponding hit test callback method is also defined.
' Capture the mouse event and hit test the coordinate point value against ' the child visual objects. Private Sub MyVisualHost_MouseLeftButtonUp(ByVal sender As Object, ByVal e As MouseButtonEventArgs) ' Retreive the coordinates of the mouse button event. Dim pt As Point = e.GetPosition(CType(sender, UIElement)) ' Initiate the hit test by setting up a hit test result callback method. VisualTreeHelper.HitTest(Me, Nothing, New HitTestResultCallback(AddressOf myCallback), New PointHitTestParameters(pt)) End Sub ' If a child visual object is hit, toggle its opacity to visually indicate a hit. Public Function myCallback(ByVal result As HitTestResult) As HitTestResultBehavior If result.VisualHit.GetType() Is GetType(DrawingVisual) Then If (CType(result.VisualHit, DrawingVisual)).Opacity = 1.0 Then CType(result.VisualHit, DrawingVisual).Opacity = 0.4 Else CType(result.VisualHit, DrawingVisual).Opacity = 1.0 End If End If ' Stop the hit test enumeration of objects in the visual tree. Return HitTestResultBehavior.Stop End Function
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.