static class Program

    {  

        private const int WS_SHOWNORMAL = ;

        [DllImport("User32.dll")]

        private static extern bool ShowWindowAsync(IntPtr hWnd, int cmdShow);

        [DllImport("User32.dll")]

        private static extern bool SetForegroundWindow(IntPtr hWnd);  

        /// <summary>

        /// 应用程序的主入口点。

        /// </summary>

        [STAThread]

        static void Main()

        {

            Process instance = GetRunningInstance();

            if (instance == null)

            {

                Application.EnableVisualStyles();

                Application.SetCompatibleTextRenderingDefault(false);

                Application.Run(new frm_Main());//在这启动主窗体。

            }

            else

            {

                HandleRunningInstance(instance);

            }

        }

        /// <summary>

        /// 获取当前是否具有相同进程。

        /// </summary>

        /// <returns></returns>

        public static Process GetRunningInstance()

        {

            Process current = Process.GetCurrentProcess();

            Process[] processes = Process.GetProcessesByName(current.ProcessName);

            //遍历正在有相同名字运行的例程

            foreach (Process process in processes)

            {

                //忽略现有的例程

                if (process.Id != current.Id)

                    //确保例程从EXE文件运行

                    if ( System.Reflection.Assembly.GetExecutingAssembly().Location.Replace("/" , "\\") == current.MainModule.FileName )

                        return process;

            }

            return null;

        }

        /// <summary>

        /// 激活原有的进程。

        /// </summary>

        /// <param name="instance"></param>

        public static void HandleRunningInstance(Process instance)

        {

            ShowWindowAsync(instance.MainWindowHandle, WS_SHOWNORMAL);

            SetForegroundWindow(instance.MainWindowHandle);

        }

    }

}