Question

I’m using the following code to detect touch points. However, when the user’s fingers completely leave the screen, my handler never gets called.

QUESTION – how do i detect that the number of touch points has become 0?

    public MainPage()
    {
        InitializeComponent();

        Touch.FrameReported += new TouchFrameEventHandler(OnFrameReported);
    }

    private void OnFrameReported(object sender, TouchFrameEventArgs e)
    {
        var args = e.GetTouchPoints(null);

Answer 1

The best answer I found is to listen to ManipulationComplete to get notified that the user is lifting their last finger. However, you will still get some trailing touch frames after that. So we need to ignore them… I just ignored the next second of them, but that’s probably overkill.

    public MainPage()
    {
        ...

        ManipulationCompleted += OnManipulationCompleted;

        ...
    }

    private void OnManipulationCompleted(object sender, ManipulationCompletedEventArgs e)
    {
        OnFrameReported(this, null);

        m_whenStopIgnoringTouchEvents = Environment.TickCount + 1000;
    }

    private void OnFrameReported(object sender, TouchFrameEventArgs e)
    {
        if (e != null)
        {
            if(Environment.TickCount > m_whenStopIgnoringTouchEvents)
            {
                // null indicates the touch point information is relative to the 
                // top left corner
                var args = e.GetTouchPoints(null);
                ...
            }
        }
    }

    private int m_whenStopIgnoringTouchEvents = 0;