c#调用winapi为外部程序控件赋值

public partial class Form1 : Form
    {
        [DllImport("user32.dll")]
        public static extern IntPtr FindWindow(string lpClassName, string lpWindowName);

        //[DllImport("User32.dll", EntryPoint = "SendMessage", CharSet = CharSet.Unicode)]
        //private static extern int SendMessage(IntPtr hwnd, uint wMsg, int wParam, int lParam);

        [DllImport("user32.dll", EntryPoint = "SendMessageA")]

        private static extern int SendMessage(IntPtr hwnd, uint wMsg, IntPtr wParam, string lParam);

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

        [DllImport("user32.dll", EntryPoint = "GetDesktopWindow", CharSet = CharSet.Auto, SetLastError = true)]
        static extern IntPtr GetDesktopWindow();

        [DllImport("user32.dll", SetLastError = true)]
        static extern IntPtr GetWindow(IntPtr hWnd, GetWindowCmd uCmd);

        [DllImport("user32.dll", CharSet = CharSet.Auto)]
        static extern int GetWindowText(IntPtr hWnd, StringBuilder lpText, int nCount);

        [DllImport("user32.dll")]
        public static extern int EnumChildWindows(IntPtr hWndParent, CallBack lpfn, int lParam);
        public delegate bool CallBack(IntPtr hwnd, int lParam);

        [DllImport("user32.dll", SetLastError = true, CharSet = CharSet.Auto)]
        static extern int GetClassName(IntPtr hWnd, StringBuilder lpClassName, int nMaxCount);



        public Form1()
        {
            InitializeComponent();
        }

        private void btnFind_Click(object sender, EventArgs e)
        {
            //1、获取桌面窗口的句柄
            IntPtr desktopPtr = GetDesktopWindow();
            //2、获得一个子窗口（这通常是一个顶层窗口，当前活动的窗口）
            IntPtr winPtr = GetWindow(desktopPtr, GetWindowCmd.GW_CHILD);

            //3、循环取得桌面下的所有子窗口
            while (winPtr != IntPtr.Zero)
            {
                StringBuilder sbs = new StringBuilder(200);
                GetWindowText(winPtr, sbs, sbs.Capacity);

                if (!String.IsNullOrEmpty(sbs.ToString()))
                {
                    if (sbs.ToString().IndexOf("自动输入") >= 0)
                    {
                        StringBuilder sbClassName = new StringBuilder(200);
                        GetClassName(winPtr, sbClassName, sbClassName.Capacity);

                        IntPtr ptrChild = IntPtr.Zero;

                        int i = EnumChildWindows(winPtr, (h, l) =>
                        {
                            StringBuilder sb = new StringBuilder(200);
                            GetWindowText(h, sb, sb.Capacity);
                            if (sb.ToString().Contains("自动输入"))
                            {
                                ptrChild = h;
                                return false;
                            }
                            else
                            {
                                return true;
                            }
                        }, 0);

                        if (ptrChild != IntPtr.Zero)
                        {
                            List<IntPtr> listEdit = new List<IntPtr>();
                            List<string> listLabel = new List<string>();
                            uint WM_SETTEXT = 0x000C;

                            IntPtr result = IntPtr.Zero;
                            do
                            {
                                result = FindWindowEx(ptrChild, result, null, null);
                                if (result != IntPtr.Zero)
                                {
                                    StringBuilder sb = new StringBuilder(200);
                                    GetWindowText(result, sb, sb.Capacity);

                                    GetClassName(result, sbClassName, sbClassName.Capacity);

                                    if (sbClassName.ToString().Contains("EDIT"))
                                    {
                                        listEdit.Add(result);
                                    }
                                    if (sbClassName.ToString().Contains("STATIC"))
                                    {
                                        listLabel.Add(sb.ToString());
                                    }
                                }

                            } while (result != IntPtr.Zero);

                            for (int j = 0; j < listLabel.Count; j++)
                            {
                                string str = listLabel[j];
                                IntPtr p = listEdit[j];
                                SendMessage(p, WM_SETTEXT, IntPtr.Zero, "");

                                string tmp = "";
                                if (str.Contains("单位名称"))
                                {
                                    tmp = textBox1.Text;
                                }
                                else if (str.Contains("识别码"))
                                {
                                    tmp = textBox2.Text;
                                }
                                else if (str.Contains("联系电话"))
                                {
                                    tmp = textBox3.Text;
                                }
                                else if (str.Contains("账户"))
                                {
                                    tmp = textBox4.Text;
                                }
                                SendMessage(p, WM_SETTEXT, IntPtr.Zero, tmp);
                            }

                        }
                    }
                }

                //4、继续获取下一个子窗口
                winPtr = GetWindow(winPtr, GetWindowCmd.GW_HWNDNEXT);

            }
        }

           }

    /// <summary>
    ///
    /// </summary>
    enum GetWindowCmd : uint
    {
         GW_HWNDFIRST = 0,
         GW_HWNDLAST = 1,
         GW_HWNDNEXT = 2,
         GW_HWNDPREV = 3,
         GW_OWNER = 4,
         GW_CHILD = 5,
         GW_ENABLEDPOPUP = 6