static class Program
    {
        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        [STAThread]
        static void Main()
        {
            bool createdNew;
            //系統能夠識別有名稱的互斥，因此可以使用它禁止應用程序啟動兩次
            //第二個參數可以設置為產品的名稱:Application.ProductName

            //每次啟動應用程序，都會驗證名稱為SingletonWinAppMutex的互斥是否存在
            Mutex mutex = new Mutex(false, "SingletonWinAppMutex", out createdNew);

            //如果已運行，則在前端顯示
            //createdNew == false，說明程序已運行
            if (!createdNew)
            {
                Process instance = GetExistProcess();
                if (instance != null)
                {
                    SetForegroud(instance);
                    Application.Exit();
                    return;
                }
            }
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new MainForm());
        }

        /// <summary>
        /// 查看程序是否已經運行
        /// </summary>
        /// <returns></returns>
        private static Process GetExistProcess()
        {
            Process currentProcess = Process.GetCurrentProcess();
            foreach (Process process in Process.GetProcessesByName(currentProcess.ProcessName))
            {
                if ((process.Id != currentProcess.Id) &&
                    (Assembly.GetExecutingAssembly().Location == currentProcess.MainModule.FileName))
                {
                    return process;
                }
            }
            return null;
        }

        /// <summary>
        /// 使程序前端顯示
        /// </summary>
        /// <param name="instance"></param>
        private static void SetForegroud(Process instance)
        {
            IntPtr mainFormHandle = instance.MainWindowHandle;
            if (mainFormHandle != IntPtr.Zero)
            {
                ShowWindowAsync(mainFormHandle, 1);
                SetForegroundWindow(mainFormHandle);
            }
        }

        [DllImport("User32.dll")]
        private static extern bool SetForegroundWindow(IntPtr hWnd);

        [DllImport("User32.dll")]
        private static extern bool ShowWindowAsync(IntPtr hWnd, int cmdShow);
    }