前端时间做了Messenger助手，后来发现只支持Windows Messenger，不支持Windows Live Messenger，最近改了一下，用到了Active Accessibility编程，代码如下：

using System;
using Accessibility;

namespace MessengerHelper
{
    /// <summary>
    /// 对Messenger窗口进行操作
    /// </summary>
    public class MessengerWindowHelper
    {
        IntPtr _messengerWindowHandle ;
        IntPtr _inputBoxHandle ;
        IntPtr _submitButtonHandle ;
        IAccessible _inputBox ;
        IAccessible _submitButton ;

        private MessengerWindowHelper(){}
        public MessengerWindowHelper(IntPtr windowHandle)
        {
            _messengerWindowHandle = windowHandle ;
            _inputBoxHandle = GetInputBoxHandle() ;
            _submitButtonHandle = GetSubmitButton() ;

            if (_inputBoxHandle == IntPtr.Zero && _submitButtonHandle == IntPtr.Zero)
            {
                GetAccessibleObjects(_messengerWindowHandle, out _inputBox, out _submitButton);
            }
        }

        /// <summary>
        /// 输入消息
        /// </summary>
        /// <param name="message"></param>
        public void InputMessage(string message)
        {
            if (_inputBox == null)
            {
                Win32.SendMessageString(_inputBoxHandle, Win32.WM_SETTEXT, IntPtr.Zero, message);            
            }
            else
            {
                _inputBox.set_accValue(Win32.CHILDID_SELF, message) ;
            }
        }

        /// <summary>
        /// 发送消息
        /// </summary>
        public void SendMessage()
        {
            if (_submitButton == null)
            {
                Win32.SendMessageInt(_submitButtonHandle, Win32.WM_CLICK, IntPtr.Zero, 0);             
            }
            else
            {
                _submitButton.accDoDefaultAction(Win32.CHILDID_SELF) ;
            }
        }

        private IntPtr GetInputBoxHandle()
        {
            IntPtr topInputHandle = Win32.FindWindowEx(_messengerWindowHandle, System.IntPtr.Zero, "RichEdit20W", null) ;
            return Win32.FindWindowEx(_messengerWindowHandle, topInputHandle, "RichEdit20W", null) ;
        }

        private IntPtr GetSubmitButton()
        {
            return Win32.FindWindowEx(_messengerWindowHandle, System.IntPtr.Zero, "Button", "发送(&S)") ;
        }

        private object[] GetAccessibleChildren(IAccessible paccContainer)
        {
            object[] rgvarChildren = new object[paccContainer.accChildCount] ;
            int pcObtained ;
　　        Win32.AccessibleChildren(paccContainer,0,paccContainer.accChildCount, rgvarChildren, out pcObtained);
            return rgvarChildren ;
        }

        private void GetAccessibleObjects(System.IntPtr imWindowHwnd, out IAccessible inputBox, out IAccessible submitButtion)
        {
            System.IntPtr ptrUIHWND = Win32.FindWindowEx(imWindowHwnd, System.IntPtr.Zero, "DirectUIHWND", 0);
            Guid guidCOM = new Guid(0x618736E0,0x3C3D,0x11CF,0x81,0xC,0x0,0xAA,0x0,0x38,0x9B,0x71);
            Accessibility.IAccessible IACurrent = null;
            
            Win32.AccessibleObjectFromWindow(ptrUIHWND,(int)Win32.OBJID_CLIENT,ref guidCOM,ref IACurrent); 
            IACurrent = (IAccessible)IACurrent.accParent;
            int childCount = IACurrent.accChildCount;
            object[] windowChildren = new object[childCount];
            int pcObtained;
            Win32.AccessibleChildren(IACurrent, 0, childCount, windowChildren, out pcObtained);

            inputBox = null ;
            submitButtion = null ;

            string accName ;
            int accRole ;
            foreach(IAccessible child in windowChildren)
            {
                accRole = (int)child.get_accRole(Win32.CHILDID_SELF) ;
                accName = child.get_accName(Win32.CHILDID_SELF) ;
                if (accRole == 10)
                {
                    object[] clientChilren = GetAccessibleChildren(child) ;                            
                    IAccessible client = (IAccessible)clientChilren[0] ;
                    clientChilren = GetAccessibleChildren(client) ;
                    
                    foreach (IAccessible childChild in clientChilren)
                    {
                        accRole = (int)childChild.get_accRole(Win32.CHILDID_SELF) ;
                        accName = childChild.get_accName(Win32.CHILDID_SELF) ;
                        
                        if (accRole == 42 && accName == "输入")
                        {
                            inputBox = childChild ;
                        }

                        if (accRole == 43 && accName == "发送按钮")
                        {
                            submitButtion = childChild ;
                        }

                        if (inputBox != null && submitButtion != null)
                        {
                            break ;
                        }
                    }                    
                    break ;
                }                        
            }            
        }
    }
}

using System;
using System.Runtime.InteropServices;

using Accessibility;

namespace MessengerHelper
{
    /// <summary>
    /// 调用Window API
    /// </summary>
    public class Win32
    {
        public const int WM_SETTEXT = 0x000C; 
        public const int WM_CLICK = 0x00F5;
 
        public const int CHILDID_SELF  = 0;
        public const int CHILDID_1   = 1;
        public const int OBJID_CLIENT  = -4;

        [DllImport("User32.dll")]
        public static extern Int32 FindWindow(String lpClassName,String lpWindowName);

        [DllImport("user32.dll", CharSet=CharSet.Auto)]
        public static extern IntPtr FindWindowEx(
            IntPtr parentHandle,
            IntPtr childAfter, 
            string lpszClass,
            int sWindowTitle  /*HWND*/);

        [DllImport("user32.dll", SetLastError = true)]
        public static extern IntPtr FindWindowEx(IntPtr parentHandle, IntPtr childAfter, string className,  string  windowTitle);        

        [DllImport("user32.dll", EntryPoint="SendMessage")] 
        public static extern int SendMessageString (IntPtr hwnd, int wMsg, IntPtr wParam, string lParam); 

        [DllImport("user32.dll", EntryPoint="SendMessage")] 
        public static extern int SendMessageInt (IntPtr hwnd, int wMsg, IntPtr wParam, int lParam); 

        [DllImport("Oleacc.dll")]
　　    public static extern int AccessibleObjectFromWindow(
　　    IntPtr hwnd,
　　    int dwObjectID,
　　    ref Guid refID,
　　    ref IAccessible ppvObject);

        [DllImport("Oleacc.dll")]
        public static extern int WindowFromAccessibleObject(
            IAccessible pacc,
            out IntPtr phwnd);
    　　
　　    [DllImport("Oleacc.dll")]
　　    public static extern int AccessibleChildren(
　　    Accessibility.IAccessible paccContainer,
　　    int iChildStart,
　　    int cChildren,
　　    [Out] object[] rgvarChildren,
　　    out int pcObtained);    
    }
}

由于微软出的Messenger产品及版本繁多，而且插件也不少，所以兼容性不是很强，实用性不大，但是，个人觉得代码还是有一些借鉴作用。