C#API控制窗体

       using  System.Runtime.InteropServices;

        [DllImport( "user32.dll" , EntryPoint =  "SendMessage" , SetLastError =  true , CharSet = CharSet.Auto)]
        private  static  extern  int  SendMessage(IntPtr hwnd,  uint  wMsg,  int  wParam,  int  lParam);

        [DllImport( "user32.dll" , EntryPoint =  "FindWindow" , SetLastError =  true )]
        private  static  extern  IntPtr FindWindow( string  lpClassName,  string  lpWindowName);

        [DllImport( "user32.dll" , EntryPoint =  "FindWindowEx" , SetLastError =  true )]
        private  static  extern  IntPtr FindWindowEx(IntPtr hwndParent,  uint  hwndChildAfter,  string  lpszClass,  string  lpszWindow);

        const  uint  BM_CLICK = 0xF5;

        private  void  DoClick()
        {
            //下面的这些参数都可以用Spy++查到
            string  lpszParentClass =  "#000000" ;  //整个窗口的类名，需要Spy++查询对应的窗口
            string  lpszParentWindow =  "使命召唤10 xxxxxxx" ;  //窗口标题，这也是要Spy++去查
            string  lpszClass_Submit =  "Button" ;  //需要查找的Button的类名，这里需要Spy++去查看是按钮还是图片什么的
            string  lpszName_Submit =  "开始游戏" ;  //需要查找的Button的标题，这里需要Spy++去查看是按钮还是图片什么的
            IntPtr ParenthWnd =  new  IntPtr(0);
            IntPtr EdithWnd =  new  IntPtr(0);
            //查到窗体，得到整个窗体
            ParenthWnd = FindWindow(lpszParentClass, lpszParentWindow);
            //判断这个窗体是否有效
            if  (!ParenthWnd.Equals(IntPtr.Zero))
            {
                //得到Button，并触发它的Click事件
                EdithWnd = FindWindowEx(ParenthWnd, ( uint )EdithWnd, lpszClass_Submit, lpszName_Submit);
                if  (!EdithWnd.Equals(IntPtr.Zero))
                {
                    SendMessage(EdithWnd, BM_CLICK, 0, 0);
                }
            }
        }

我看网上的资料说可以这么做：取到button的句柄 然后用API SendMessage发送 WM_LBUTTONDOWN和WM_LBUTTONUP模拟点击具体的代码怎么写呢？