Visual Studio C# Windows Forms Application touch screen exception error

Question

I have Windows Forms Visual Studio Project; I have added the code to be able to use a finger instead of the mouse on touch screen monitor.

When I use a mouse, everything is working, but when I use a finger to top and double top on the screen also working only if I do it on any item on the form, but wh

en I use a finger on a form (on the empty space) I get an exception error, I attached a picture as well as code for the finger as a pointer.

Anyone knows what should be done, thanks in advance.

Code Here:

protected override void WndProc(ref Message m)

{

    switch (m.Msg)

    {

        case Win32.WM_POINTERDOWN:

        case Win32.WM_POINTERUP:

        case Win32.WM_POINTERUPDATE:

        case Win32.WM_POINTERCAPTURECHANGED:

            break;

        default:

            base.WndProc(ref m);

            return;

    }

    int pointerID = Win32.GET_POINTER_ID(m.WParam);

    Win32.POINTER_INFO pi = new Win32.POINTER_INFO();

    if (!Win32.GetPointerInfo(pointerID, ref pi))

    {

        Win32.CheckLastError();

    }

    Point pt = PointToClient(pi.PtPixelLocation.ToPoint());

    MouseEventArgs me = new MouseEventArgs(System.Windows.Forms.MouseButtons.Left, 1, pt.X, pt.Y, 0);

    switch (m.Msg)

    {

        case Win32.WM_POINTERDOWN:

            Console.WriteLine("TOCOU" + pt);

            (Parent as Form1).Form1_MouseDown((this as object), me);

            break;

        case Win32.WM_POINTERUP:

            Console.WriteLine("LEVANTOU");

            (Parent as Form1).Form1_MouseUp((this as object), me);

            break;

        case Win32.WM_POINTERUPDATE:

            Console.WriteLine("UPDATE");

            (Parent as Form1).Form1_MouseMove((this as object), me);

            break;

    }

}

Answer 1

Hi @Gennady Gurin , Welcome to Microsoft Q&A,

When touching in the blank area, there is no target control to receive the message, which may cause an exception. If the Parent object is not of Form1 type, the forced conversion will fail. To ensure that Parent is of Form1 type, you can use the as keyword and perform type checking.

protected override void WndProc(ref Message m)
{
    Form1 parentForm = Parent as Form1;

    switch (m.Msg)
    {
        case Win32.WM_POINTERDOWN:
        case Win32.WM_POINTERUP:
        case Win32.WM_POINTERUPDATE:
        case Win32.WM_POINTERCAPTURECHANGED:
            break;
        default:
            base.WndProc(ref m);
            return;
    }

    int pointerID = Win32.GET_POINTER_ID(m.WParam);
    Win32.POINTER_INFO pi = new Win32.POINTER_INFO();
    if (!Win32.GetPointerInfo(pointerID, ref pi))
    {
        Win32.CheckLastError();
        return;
    }

    Point pt = PointToClient(pi.PtPixelLocation.ToPoint());
    MouseEventArgs me = new MouseEventArgs(System.Windows.Forms.MouseButtons.Left, 1, pt.X, pt.Y, 0);

    if (parentForm != null)
    {
        switch (m.Msg)
        {
            case Win32.WM_POINTERDOWN:
                Console.WriteLine("TOCOU" + pt);
                parentForm.Form1_MouseDown(this, me);
                break;

            case Win32.WM_POINTERUP:
                Console.WriteLine("LEVANTOU");
                parentForm.Form1_MouseUp(this, me);
                break;

            case Win32.WM_POINTERUPDATE:
                Console.WriteLine("UPDATE");
                parentForm.Form1_MouseMove(this, me);
                break;
        }
    }
    else
    {
        Console.WriteLine("Parent form is not of type Form1.");
    }
}

Best Regards,

Jiale

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