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)
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
Available since 3.0