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PostMessage doesn't seem to work

I am trying to use PostMessage to send a tab key.

Here is my code:

// This class allows us to send a tab key when the the enter key
//  is pressed for the mooseworks mask control.   
public class MaskKeyControl : MaskedEdit
{
//  [DllImport("coredll.dll", SetLastError = true, CharSet = CharSet.Auto)]
//  static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, Int32 wParam, Int32 lParam);

    [return: MarshalAs(UnmanagedType.Bool)]
    // I am calling this on a Windows Mobile device so the dll is coredll.dll
    [DllImport("coredll.dll", SetLastError = true)]
    static extern bool PostMessage(IntPtr hWnd, uint Msg, Int32 wParam, Int32 lParam);

    public const Int32 VK_TAB = 0x09;
    public const Int32 WM_KEYDOWN = 0x100;

    protected override void OnKeyDown(KeyEventArgs e)
    {
        if (e.KeyData == Keys.Enter)
        {
            PostMessage(this.Handle, WM_KEYDOWN, VK_TAB, 0);
            return;
        }
        base.OnKeyDown(e);
    }

    protected override void OnKeyPress(KeyPressEventArgs e)
    {
        if (e.KeyChar == '\r') 
            e.Handled = true;
        base.OnKeyPress(e);
    }
}

When I hit the enter button, the code gets called but nothing happens. Then I press TAB and it works fine. (So ​​there is something wrong with my tab message sending.)

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3 answers


You really shouldn't send Windows messages related to user input directly to Windows controls. Rather, if you want to simulate input, you must instead rely on the SendInput API function to send keystrokes.



Also, as Chris Taylor mentions in his comment, the SendKeys class can be used to send key inputs to the application in case you want to use an existing managed wrapper (instead of calling the SendInput function yourself through the P / Invoke layer).

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PostMessage for key events is really really weird.



In this case, perhaps SendMessage with KEYDOWN, KEYPRESS, KEYUP (three calls) might work better.

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An alternative to sending input messages to the control could be more explicit and do the following.

protected override void OnKeyDown(KeyEventArgs e)
{
  if (e.KeyCode == Keys.Enter)
  {
    if (Parent != null)
    {
      Control nextControl = Parent.GetNextControl(this, true);
      if (nextControl != null)
      {
        nextControl.Focus();
        return;
      }
    }
  }
  base.OnKeyDown(e);
}

Pressing enter will set focus to the next parent control.

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