问C#应用程序延迟Win7交换机用户

EN

[DllImport("WtsApi32.dll")]
public static extern bool WTSRegisterSessionNotification(IntPtr hWnd, [MarshalAs(UnmanagedType.U4)]int dwFlags);

[DllImport("WtsApi32.dll")]
public static extern bool WTSUnRegisterSessionNotification(IntPtr hWnd);

WTSRegisterSessionNotification(this.Handle, 1); // all sessions

protected override void WndProc(ref Message m)
{
    switch (m.Msg)
    {
        case Unmanaged.Constants.WM_WTSSESSION_CHANGE: // 0x02B1
            {
                try
                {
                    int wParamValue = m.WParam.ToInt32();
                    File.AppendAllText(@"d:\temp\logoff.txt", wParamValue.ToString());

                    if (wParamValue == Unmanaged.Constants.SESSION_LOCK)// SESSION_LOCK = 0x7;
                    {
                        DialogResult dialogResult = MessageBox.Show(this, 
                            "Do you really want to switch user?",
                            "title", MessageBoxButtons.YesNo, MessageBoxIcon.Question);

                        if (dialogResult == DialogResult.No)
                        {
                            // cancel switch user
                            return;
                        }
                    }
                }
                catch (Exception exc)
                {
                    break;
                }
                break;
            }
    }

    base.WndProc(ref m);
}