用Sendmessage发送或截取相关消息

关键步骤是覆盖DefWndProc的消息预处理事件。如下，我们定义一个自己的消息进行处理 。

1.引用Sendmessage并定义一个消息

 [DllImport("user32.dll")]
        public static extern int SendMessage(IntPtr hWnd, uint Msg, uint wParam, uint Lparam);
        private const int WM_User=0x0400+101;

2.覆盖DefWndProc事件

 protected override void DefWndProc(ref Message m)
        {
            switch (m.Msg)
            {
                case WM_User:
                    MessageBox.Show("User's Message");
                    break;
                 default:
                    base.DefWndProc(ref m);
                    break;
            }
            
        }

3.调用SendMessage事件
  

 private void button1_Click(object sender, EventArgs e)
        {
            SendMessage(Handle, WM_User, 0, 0);
        }