TouchFrameEventArgs.GetPrimaryTouchPoint(IInputElement) 方法

定義

命名空間:

System.Windows.Input

組件:

PresentationCore.dll

傳回主要觸控裝置目前相對於指定之項目的觸控點。

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.TouchPoint

Public Function GetPrimaryTouchPoint (relativeTo As IInputElement) As TouchPoint

參數

relativeTo

IInputElement

會定義座標空間的項目。 若要使用 WPF 絕對座標，請將 relativeTo 指定為 null。

傳回

TouchPoint

主要 TouchDevice 目前相對於指定項目的位置，如果主要 TouchDevice 不在作用中，則為 null。

範例

下列程式代碼會處理從擷取的 TouchFrameEventArgs觸控點。 在上 Canvas按下觸控時，會 TouchDevice 擷取至 Canvas。 當觸控隨即放開時， TouchDevice 會放開 。 當觸控在 之間 Canvas移動時， Id 會檢查 。 Id如果 符合Id主要觸控點的 ，表示第一次觸控，則會記錄其位置。 如果移動來自第二個觸控，則會從第一個觸控的位置繪製線條到第二個觸控的位置。

這個範例是類別概觀中可用的較大範例的 Touch 一部分。

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

備註

在一組作用中的觸控裝置中，第一個 Activated 裝置是主要觸控裝置。 例如，如果兩指觸碰螢幕，則向下的第一個手指是由主要觸控裝置表示。 如果第一個手指在第二個手指仍然關閉時隨即增益，則主要觸控裝置會 null變成 。