获取窗体的搜有控件句柄

如何获取该窗体上盘符地址栏,和搜索栏控件的句柄,并发消息去改变盘符路径和搜索的文件值

 const int WM_SETTEXT = 0x000C;
        const int WM_LBUTTONDOWN = 0x0201;
        const int WM_LBUTTONUP = 0x0202;
        const int WM_CLOSE = 0x0010;

        [DllImport("user32.dll")]
        public static extern IntPtr FindWindow(string lpClassName, string lpWindowName);

        [DllImport("User32.dll", EntryPoint = "SendMessage")]
        private static extern int SendMessage(IntPtr hWnd, int Msg, IntPtr wParam, string lParam);

        [DllImport("User32.dll ")]
        public static extern IntPtr FindWindowEx(IntPtr parent, IntPtr childe, string strclass, string FrmText);

        private void button1_Click(object sender, EventArgs e)
        {
            IntPtr hwnd = FindWindow("CabinetWClass", null);
            IntPtr htextbox = FindWindowEx(hwnd, IntPtr.Zero, "EDIT", null);
            SendMessage(htextbox, WM_SETTEXT, IntPtr.Zero, "name");

            IntPtr hbutton = FindWindowEx(hwnd, IntPtr.Zero, "BUTTON", null);
            SendMessage(hbutton, WM_LBUTTONDOWN, IntPtr.Zero, null);
            SendMessage(hbutton, WM_LBUTTONUP, IntPtr.Zero, null);
        }

这样为什么获取不到,应该如何获取 窗体 控件 句柄

补充：.NET技术 ,  C#