ManipulationDeltaEventArgs.ReportBoundaryFeedback Method (ManipulationDelta)

.NET Framework (current version)

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Specifies that the manipulation has gone beyond certain boundaries.

Namespace:   System.Windows.Input
Assembly:  PresentationCore (in PresentationCore.dll)

Public Sub ReportBoundaryFeedback (
	unusedManipulation As ManipulationDelta


Type: System.Windows.Input.ManipulationDelta

The portion of the manipulation that represents moving beyond the boundary.

Exception Condition

unusedManipulation is null.

Use the ReportBoundaryFeedback method to indicate that an element has moved beyond a certain boundary. For example, if a user moves an element outside of the bounds of a Window, you can call this method to report that to the window. When you call ReportBoundaryFeedback, the ManipulationBoundaryFeedback event occurs. By default, the Window subscribes to the ManipulationBoundaryFeedback event to provide visual feedback to the user that a boundary has been reached. You can subscribe to ManipulationBoundaryFeedback to implement custom behavior.

The following example shows an event handler for the ManipulationDelta event that calls the ReportBoundaryFeedback method when the user moves the element over the edge of its container. To test this example, follow the steps in Walkthrough: Creating Your First Touch Application and replace the code in step 5 with this code.

Private Sub Window_ManipulationDelta(ByVal sender As Object, ByVal e As ManipulationDeltaEventArgs)

    Dim rectToMove As Rectangle = TryCast(e.OriginalSource, Rectangle)
    Dim overshoot As Vector

    ' When the element crosses the boundary of the window, check whether 
    ' the manipulation is in inertia. If it is, complete the manipulation.
    ' Otherwise, report the boundary feedback.
    If CalculateOvershoot(rectToMove, e.ManipulationContainer, overshoot) Then
        If e.IsInertial Then
            e.Handled = True
            Exit Sub
            'Report that the element hit the boundary

            e.ReportBoundaryFeedback(New ManipulationDelta(overshoot, 0, New Vector(), New Vector()))
        End If
    End If

    ' Move the element as usual.

    ' Get the Rectangle and its RenderTransform matrix.
    Dim rectsMatrix As Matrix = DirectCast(rectToMove.RenderTransform, MatrixTransform).Matrix

    ' Rotate the Rectangle.
    rectsMatrix.RotateAt(e.DeltaManipulation.Rotation, e.ManipulationOrigin.X, e.ManipulationOrigin.Y)

    ' Resize the Rectangle. Keep it square 
    ' so use only the X value of Scale.
    rectsMatrix.ScaleAt(e.DeltaManipulation.Scale.X, e.DeltaManipulation.Scale.X, e.ManipulationOrigin.X, e.ManipulationOrigin.Y)

    ' Move the Rectangle.
    rectsMatrix.Translate(e.DeltaManipulation.Translation.X, e.DeltaManipulation.Translation.Y)

    ' Apply the changes to the Rectangle.
    rectToMove.RenderTransform = New MatrixTransform(rectsMatrix)

    e.Handled = True
End Sub

Private Function CalculateOvershoot(ByVal element As UIElement, ByVal container As IInputElement, ByRef overshoot As Vector) As Boolean
    ' Get axis aligned element bounds
    Dim elementBounds = element.RenderTransform.TransformBounds(VisualTreeHelper.GetDrawing(element).Bounds)

    'double extraX = 0.0, extraY = 0.0;
    overshoot = New Vector()

    Dim parent As FrameworkElement = TryCast(container, FrameworkElement)
    If parent Is Nothing Then
        Return False
    End If

    ' Calculate overshoot. 
    If elementBounds.Left < 0 Then
        overshoot.X = elementBounds.Left
    ElseIf elementBounds.Right > parent.ActualWidth Then
        overshoot.X = elementBounds.Right - parent.ActualWidth
    End If

    If elementBounds.Top < 0 Then
        overshoot.Y = elementBounds.Top
    ElseIf elementBounds.Bottom > parent.ActualHeight Then
        overshoot.Y = elementBounds.Bottom - parent.ActualHeight
    End If

    ' Return false if Overshoot is empty; otherwsie, return true.
    Return Not Vector.Equals(overshoot, New Vector())
End Function

.NET Framework
Available since 4.0
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