获取基于Internet Explorer_Server的聊天窗口内容

假设在得到窗体中控件的句柄（通过SPY++）的前提下，如果是像文本框这种控件，只要用SendMessage就可得到文本了，但是对于聊天记录窗口却行不通（返回空值），因为那其实是一个内置浏览器Internet Explorer_Server

经查询，可用以下方式获取：

先引用：mshtml

using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;
using mshtml;

   [Flags]
    public enum SendMessageTimeoutFlags : uint
    {
        SMTO_NORMAL = 0x0,
        SMTO_BLOCK = 0x1,
        SMTO_ABORTIFHUNG = 0x2,
        SMTO_NOTIMEOUTIFNOTHUNG = 0x8
    }

public class WinAPI
{
        [DllImport("user32.dll", SetLastError = true, CharSet = CharSet.Auto)]
        static extern uint RegisterWindowMessage(string lpString);      

        [DllImport("user32.dll", SetLastError = true, CharSet = CharSet.Auto)]
        private static extern IntPtr SendMessageTimeout(IntPtr hWnd, uint Msg, IntPtr wParam, IntPtr lParam, SendMessageTimeoutFlags flags, uint timeout, out UIntPtr result);

        [DllImport("oleacc.dll", PreserveSig = false)]
        [return: MarshalAs(UnmanagedType.Interface)]
        private static extern object ObjectFromLresult(UIntPtr lResult, [MarshalAs(UnmanagedType.LPStruct)] Guid refiid, IntPtr wParam);

        public IHTMLDocument2 GetHtmlDocument(IntPtr hWnd)
        {
            uint lMsg = RegisterWindowMessage("WM_HTML_GETOBJECT");

            UIntPtr lRes;
            SendMessageTimeout(hWnd, lMsg, IntPtr.Zero, IntPtr.Zero, SendMessageTimeoutFlags.SMTO_ABORTIFHUNG, , out lRes);

            IHTMLDocument2 htmlDoc = null;
            if (lRes != UIntPtr.Zero)
            {
                htmlDoc = (IHTMLDocument2)ObjectFromLresult(lRes, typeof(IHTMLDocument2).GUID, IntPtr.Zero);
            }

            return htmlDoc;
        }

        public string GetWebText(IntPtr hWnd)
        {
            IHTMLDocument2 htmlDoc = GetHtmlDocument(hWnd);
            if (htmlDoc != null)
            {
                return htmlDoc.body.innerHTML;
            }
            else
            {
                return string.Empty;
            }
        }
}