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TouchFrameEventArgs.GetTouchPoints Method

Returns a collection that contains the current touch point for each active touch device relative to the specified element.

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

'Declaration
Public Function GetTouchPoints ( _
	relativeTo As IInputElement _
) As TouchPointCollection

Parameters

relativeTo
Type: System.Windows.IInputElement

The element that defines the coordinate space. To use WPF absolute coordinates, specify relativeTo as Nothing.

Return Value

Type: System.Windows.Input.TouchPointCollection
A collection that contains the current TouchPoint for each active TouchDevice.

The following code processes the touch points retrieved from the TouchFrameEventArgs. When a touch is pressed on the canvas, the TouchDevice is captured to the canvas. When the touch is raised, the TouchDevice is released. When a touch moves across the canvas, the Id is checked. If the Id matches the Id of the primary touch point, which indicates the first touch, its location is recorded. If the move came from the second touch, a line is drawn from the position of the first touch to the position of the second touch.

This example is part of a larger example that is available in the Touch class overview.

For Each _touchPoint In e.GetTouchPoints(Me.canvas1)

    If _touchPoint.Action = TouchAction.Down Then 
        ' Clear the canvas and capture the touch to it.
        canvas1.Children.Clear()
        _touchPoint.TouchDevice.Capture(canvas1)

    ElseIf _touchPoint.Action = TouchAction.Move Then 
        ' This is the first (primary) touch point. Just record its position. 
        If _touchPoint.TouchDevice.Id = e.GetPrimaryTouchPoint(Me.canvas1).TouchDevice.Id Then
            pt1.X = _touchPoint.Position.X
            pt1.Y = _touchPoint.Position.Y

            ' This is not the first touch point; draw a line from the first point to this one. 
        ElseIf _touchPoint.TouchDevice.Id <> e.GetPrimaryTouchPoint(Me.canvas1).TouchDevice.Id Then
            pt2.X = _touchPoint.Position.X
            pt2.Y = _touchPoint.Position.Y

            Dim _line As New Line()
            _line.Stroke = New RadialGradientBrush(Colors.White, Colors.Black)
            _line.X1 = pt1.X
            _line.X2 = pt2.X
            _line.Y1 = pt1.Y
            _line.Y2 = pt2.Y

            _line.StrokeThickness = 2
            Me.canvas1.Children.Add(_line)
        End If 

    ElseIf _touchPoint.Action = TouchAction.Up Then 
        ' If this touch is captured to the canvas, release it. 
        If (_touchPoint.TouchDevice.Captured Is canvas1) Then
            canvas1.ReleaseTouchCapture(_touchPoint.TouchDevice)
        End If 
    End If 
Next

.NET Framework

Supported in: 4.6, 4.5, 4

.NET Framework Client Profile

Supported in: 4
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