How do I close the on-screen keyboard process from C# winform correctly?

Question

I'm currently designing an image viewer that allows the user to input her e-mail and get the images digitally. The part that troubles me is getting the on-screen keyboard to close. I use this piece of code to start the windows process:

string progFiles = @"C:\Program Files\Common Files\Microsoft Shared\ink";
string keyboardPath = Path.Combine(progFiles, "TabTip.exe");
Process keyboardProc = Process.Start(keyboardPath);

After which i open a VB InputBox to prompt for the e-mail address (for which i use the on-screen keyboard, since the application will be shown on a touch screen). After this prompt I want to close the process automatically.

I've tried to close the process with the following:

keyboardProc.Kill();
keyboardProc.Dispose();
keyboardProc.Close();
keyboardProc = null;

None of them works and simply throws the exception:

An unhandled exception of type 'System.InvalidOperationException' occurred in System.dll
Additional information: Cannot process request because the process has exited.

I also tried identifying the process by ID and closing it this way, didn't work either. I also had a look at: C#/.NET: Closing another process outside the main window but didn't get it working either.. :(

I'm pretty new to C# and this is the first time I've invoked a windows process from code - am I missing something?

Thank you very much in advance!

Answer 1

    /// <summary>
    /// Show the On Screen Keyboard
    /// </summary>
    #region ShowOSK
    public static void ShowOnScreenKeyboard()
    {
        ProcessStartInfo startInfo = new ProcessStartInfo(@"C:\Program Files\Common Files\Microsoft Shared\ink\TabTip.exe");
        Process.Start(startInfo);
    }
    #endregion ShowOSK

    /// <summary>
    /// Hide the On Screen Keyboard
    /// </summary>
    #region HideOSK
    public static void HideOnScreenKeyboard()
    {
        uint WM_SYSCOMMAND = 274;
        uint SC_CLOSE = 61536;
        IntPtr KeyboardWnd = FindWindow("IPTip_Main_Window", null);
        PostMessage(KeyboardWnd.ToInt32(), WM_SYSCOMMAND, (int)SC_CLOSE, 0);
    }
    #endregion HideOSK