C#服务程序FolderBrowserDialog看不见目录树解决方法

C#服务程序FolderBrowserDialog看不见目录树
我写的C#服务程序里用到了FolderBrowserDialog，但是看不见目录树
服务代码如下：

C# code

        protected override void OnStart(string[] args)        {            // TODO: 在此处添加代码以启动服务。            mainThread = new Thread(new ThreadStart(FormShow));            mainThread.Start();        }void      FormShow()        {            GetDesktopWindow();            IntPtr hwinstaSave = GetProcessWindowStation();            IntPtr dwThreadId = GetCurrentThreadId();            IntPtr hdeskSave = GetThreadDesktop(dwThreadId);            IntPtr hwinstaUser = OpenWindowStation("WinSta0", false, 33554432);            if (hwinstaUser == IntPtr.Zero)            {                RpcRevertToSelf();                return;            }            SetProcessWindowStation(hwinstaUser);            IntPtr hdeskUser = OpenDesktop("Default", 0, false, 33554432);            RpcRevertToSelf();            if (hdeskUser == IntPtr.Zero)            {                SetProcessWindowStation(hwinstaSave);                CloseWindowStation(hwinstaUser);                return;            }            SetThreadDesktop(hdeskUser);            IntPtr dwGuiThreadId = dwThreadId;            fm = new FormMain();            Application.Run(fm);            dwGuiThreadId = IntPtr.Zero;            SetThreadDesktop(hdeskSave);            SetProcessWindowStation(hwinstaSave);            CloseDesktop(hdeskUser);            CloseWindowStation(hwinstaUser);        }

C# code

private void button1_Click(object sender, EventArgs e)        {            FolderBrowserDialog fb = new FolderBrowserDialog();            fb.ShowNewFolderButton = true;            fb.RootFolder = Environment.SpecialFolder.Desktop;            if(fb.ShowDialog() == DialogResult.OK)            {                this.textBox1.Text = fb.SelectedPath;            }        }