在C#中向windows窗体发送消息示例

// define
[DllImport("User32.dll")]
        public static extern IntPtr FindWindow(String lpClassName, String lpWindowName);

        [DllImport("User32.dll")]
        static extern IntPtr FindWindowEx(IntPtr hwndParent, IntPtr hwndChildAfter, string lpszClass, string lpszWindow);

        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = false)]
        static extern IntPtr SendMessage(IntPtr hWnd, uint Msg, IntPtr wParam, IntPtr lParam);

        const int WM_LBUTTONDOWN = 0x201;
        const int WM_LBUTTONUP = 0x0202;

  // sample, u should use spy++ to find windows class name and control class name

        IntPtr hwndWin = FindWindow("TfrmMain", "window title");
            if (hwndWin.Equals(IntPtr.Zero) == false)
            {
                IntPtr hwndBtn = FindWindowEx(hwndWin, IntPtr.Zero, "TButton", "control text");
                if (hwndBtn.Equals(IntPtr.Zero) == false)
                {
                    SendMessage(hwndBtn, WM_LBUTTONDOWN, IntPtr.Zero, IntPtr.Zero);
                    SendMessage(hwndBtn, WM_LBUTTONUP, IntPtr.Zero, IntPtr.Zero);
                }
            }