c# – PostMessage似乎不起作用

这是我的代码：

// 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 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);
    }
}

当我按下输入时,代码被调用,但没有任何反应.然后我按TAB,它工作正常. (所以我发送Tab消息有问题.)