只允许运行一个客户端实例

 internal static class Program    {        /// <summary>        /// 应用程序的主入口点。        /// </summary>        [STAThread]        private static void Main()        {            Application.EnableVisualStyles();            Application.SetCompatibleTextRenderingDefault(false);            SysHelper.RunFrmOnly<FrmMain>();        }    }    public static class SysHelper    {        /// <summary>        /// 唯一运行一个实例,第二次打开时会把首次运行的置顶        /// 缺陷：(1)应用程序改名后无效  (2)如果首次运行的界面最大化，置顶时，界面会缩小，需要手动调整        /// </summary>        /// <typeparam name="T">运行的窗体</typeparam>        public static void RunFrmOnly<T>() where T : new()        {            Process instance = RunningInstance();            if (instance == null)            {                Form frm = new T() as Form;                Application.Run(frm);            }            else            {                HandleRunningInstance(instance);            }        }        [DllImport("User32.dll")]        private static extern bool SetForegroundWindow(IntPtr hWnd);        [DllImport("User32.dll")]        private static extern bool ShowWindowAsync(IntPtr hWnd, int cmdShow);        private static void HandleRunningInstance(Process instance)        {            // 确保窗口没有被最小化或最大化            ShowWindowAsync(instance.MainWindowHandle, 4);            // 设置真实例程为foreground  window            SetForegroundWindow(instance.MainWindowHandle); // 放到最前端        }        private static Process RunningInstance()        {            Process current = Process.GetCurrentProcess();            Process[] processes = Process.GetProcessesByName(current.ProcessName);            return processes.Where(process => process.Id != current.Id).FirstOrDefault(                process => Assembly.GetExecutingAssembly().Location.Replace("/", "\\") == current.MainModule.FileName);        }    }