public partial class Form1 : Form

 {

//设置文本内容的消息

private const int WM_SETTEXT = 0x000C;

 //鼠标点击消息

const int BM_CLICK = 0x00F5;[DllImport("user32.dll")]

private static extern IntPtr FindWindow(

  string lpClassName,

  string lpWindowName);

[DllImport("User32.dll")]

private static extern IntPtr FindWindowEx(

  IntPtr hwndParent,

  IntPtr hwndChildAfter,

  string lpszClass,

string lpszWindows);

[DllImport("User32.dll")]

private static extern Int32 SendMessage(

  IntPtr hWnd,       

  int Msg,       

  IntPtr wParam,      

StringBuilder lParam);

        [DllImport("user32.dll ", CharSet = CharSet.Unicode)]

        public static extern IntPtr PostMessage(IntPtr hwnd, int wMsg, IntPtr wParam, IntPtr lParam);

pri}vate

 void button1_Click(object sender, EventArgs e)

{

  // 返回写字板主窗口句柄

  IntPtr hWnd = FindWindow("Notepad", "Untitled - Notepad");

  if (!hWnd.Equals(IntPtr.Zero))

  {

    //返回写字板编辑窗口句柄

    IntPtr edithWnd = FindWindowEx(hWnd, IntPtr.Zero, "Edit", null);

    if (!edithWnd.Equals(IntPtr.Zero))

      // 发送WM_SETTEXT 消息： "Hello World!"

      SendMessage(edithWnd, WM_SETTEXT, IntPtr.Zero, new StringBuilder("Hello World!"));

  }

}

}

 

另：

 Message msg = Message.Create(hwnd_button, BM_CLICK, new IntPtr(0), new IntPtr(0));

//点击hwnd_button句柄对应的按钮

 PostMessage(msg.HWnd, msg.Msg, msg.WParam, msg.LParam);