C#服务获取不了当前激活窗口句柄

C# code

[DllImport("user32.dll", CharSet = CharSet.Auto, ExactSpelling = true)]public static extern IntPtr GetForegroundWindow();//获取当前激活窗口//获取窗口标题[DllImport("user32", SetLastError = true)]public static extern int GetWindowText(IntPtr hWnd, //窗口句柄StringBuilder lpString, //标题int nMaxCount  //最大值);//获取类的名字[DllImport("user32.dll")]private static extern int GetClassName(    IntPtr hWnd, //句柄    StringBuilder lpString, //类名    int nMaxCount //最大值);[DllImport("user32.dll")][return: MarshalAs(UnmanagedType.Bool)]static extern bool GetWindowRect(IntPtr hWnd, ref RECT lpRect);private void getAllProcess(object sender, ElapsedEventArgs e)        {            allprocess = Process.GetProcesses();            foreach (Process pro in allprocess)            {                                string pName = pro.ProcessName;                               if (pName == "QQ")                {                    try                    {                                                IntPtr formHandle = GetForegroundWindow();                        StringBuilder title = new StringBuilder(256);                        GetWindowText(formHandle, title, title.Capacity);//得到窗口的标题                        StringBuilder className = new StringBuilder(256);                        GetClassName(formHandle, className, className.Capacity);//得到窗口的句柄                                                RECT rc = new RECT();                        GetWindowRect(formHandle, ref rc);                        string formName = className.ToString();                        string fileSavePath = @"D:\image\qqimage/";                        publicDll.logMsg("QQ:开始查找 " + className, logMsgType.Normal);                        publicDll.logMsg("QQ:是否截图 " + title, logMsgType.Normal);                             if (formName.EndsWith("TXGuiFoundation"))                        {                            publicDll.logMsg("TXGuiFoundation:" + pName, logMsgType.Normal);                            if (!System.IO.Directory.Exists(fileSavePath))                            {                                System.IO.Directory.CreateDirectory(fileSavePath);                            }                            GetImageFromScreen();//截图                        }                    }                    catch (Exception ex)                    {                        publicDll.logMsg("Error:" + ex.Message, logMsgType.Normal);                    }                }            }        }

以上代码，我设定每隔2秒自动获取当前激活的窗口并截图保存，
在winform 中执行没问题，写成控制台程序执行也么问题，
但是写成服务形式就不行了，编译不会报错，但是
publicDll.logMsg("QQ:开始查找 " + , logMsgType.Normal);
publicDll.logMsg("QQ:是否截图 " + title, logMsgType.Normal);

日志发现 className title 为空导致（winform 或者控制台时候就不会），求大神看看。。。

难道服务不能用这个？？

[解决办法]

C# code

using System;using System.Runtime.InteropServices;using System.ServiceProcess;using System.Text;using System.Threading;namespace WindowsService1{    public partial class Service1 : ServiceBase    {        private Boolean _bStart;        [DllImport("user32.dll")]        public static extern IntPtr GetForegroundWindow();//获取当前激活窗口        //获取窗口标题        [DllImport("user32", SetLastError = true)]        public static extern int GetWindowText(        IntPtr hWnd, //窗口句柄        StringBuilder lpString, //标题        int nMaxCount  //最大值        );        //获取类的名字        [DllImport("user32.dll")]        private static extern int GetClassName(            IntPtr hWnd, //句柄            StringBuilder lpString, //类名            int nMaxCount //最大值        );        public Service1()        {            InitializeComponent();        }        protected override void OnStart(string[] args)        {            _bStart = true;            ThreadPool.QueueUserWorkItem(new WaitCallback((obj) =>                {                    IntPtr curHwnd = IntPtr.Zero;                    IntPtr lastHwnd = IntPtr.Zero;                    while (_bStart)                    {                        curHwnd = GetForegroundWindow();                        if (curHwnd != IntPtr.Zero && curHwnd != lastHwnd)                        {                            lastHwnd = curHwnd;                            StringBuilder sb = new StringBuilder(255);                            GetWindowText(curHwnd, sb, 255);                            if (sb.Length > 0)                            {                                System.IO.File.AppendAllText("c:\\log.txt", String.Format("{0}\r\n", sb.ToString()));                            }                        }                    }                }                ), null);        }        protected override void OnStop()        {            _bStart = false;        }    }}