TouchFrameEventArgs.GetPrimaryTouchPoint(IInputElement) Method
Definition
Important
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Returns the current touch point of the primary touch device relative to the specified element.
public:
System::Windows::Input::TouchPoint ^ GetPrimaryTouchPoint(System::Windows::IInputElement ^ relativeTo);public System.Windows.Input.TouchPoint GetPrimaryTouchPoint (System.Windows.IInputElement relativeTo);member this.GetPrimaryTouchPoint : System.Windows.IInputElement -> System.Windows.Input.TouchPointPublic Function GetPrimaryTouchPoint (relativeTo As IInputElement) As TouchPointParameters
- relativeTo
- IInputElement
The element that defines the coordinate space. To use WPF absolute coordinates, specify relativeTo as null.
Returns
The current position of the primary TouchDevice relative to the specified element; or null if the primary TouchDevice is not active.
Examples
The following code processes the touch points that are retrieved from the TouchFrameEventArgs. When a touch is pressed on the Canvas, the TouchDevice is captured to the Canvas. When the touch is lifted, 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.
foreach (TouchPoint _touchPoint in e.GetTouchPoints(this.canvas1))
{
if (_touchPoint.Action == TouchAction.Down)
{
// Clear the canvas and capture the touch to it.
this.canvas1.Children.Clear();
_touchPoint.TouchDevice.Capture(this.canvas1);
}
else if (_touchPoint.Action == TouchAction.Move && e.GetPrimaryTouchPoint(this.canvas1) != null)
{
// This is the first (primary) touch point. Just record its position.
if (_touchPoint.TouchDevice.Id == e.GetPrimaryTouchPoint(this.canvas1).TouchDevice.Id)
{
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.
else if (_touchPoint.TouchDevice.Id != e.GetPrimaryTouchPoint(this.canvas1).TouchDevice.Id)
{
pt2.X = _touchPoint.Position.X;
pt2.Y = _touchPoint.Position.Y;
Line _line = 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;
this.canvas1.Children.Add(_line);
}
}
else if (_touchPoint.Action == TouchAction.Up)
{
// If this touch is captured to the canvas, release it.
if (_touchPoint.TouchDevice.Captured == this.canvas1)
{
this.canvas1.ReleaseTouchCapture(_touchPoint.TouchDevice);
}
}
}
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
Remarks
In a set of active touch devices, the first device to be Activated is the primary touch device. For example, if two fingers are touching the screen, the first finger that is down is represented by the primary touch device. If the first finger is lifted while the second finger is still down, the primary touch device becomes null.
