如何只运行一个实例

如何只运行一个实例，而在第二次和以后运行时激活原程序而不重新创建一个新实例，本文收集来源于internet

调用实现类

            Process p = DCSingleInstance.GetRunningInstance();
            if (p != null)
            {
                DCSingleInstance.HandleRunningInstance(p);
                return;
            }

 DCSingleInstance.GetRunningInstance();
            if (p != null)
            {
                DCSingleInstance.HandleRunningInstance(p);
                return;
            }

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

        private const int WS_SHOWNORMAL = 1;


        public static Process GetRunningInstance()
        {
            Process currentProcess = Process.GetCurrentProcess();
            string currentFileName = currentProcess.MainModule.FileName;
            Process[] processes = Process.GetProcessesByName(currentProcess.ProcessName);
            foreach (Process process in processes)
            {
                if (process.MainModule.FileName == currentFileName)
                {
                    if (process.Id != currentProcess.Id)
                        return process;
                }
            }
            return null;
        }


        public static bool HandleRunningInstance(Process instance)
        {

            ShowWindowAsync(instance.MainWindowHandle, WS_SHOWNORMAL);
            return SetForegroundWindow(instance.MainWindowHandle);
        }

        public static bool HandleRunningInstance()
        {
            Process p = GetRunningInstance();
            if (p != null)
            {
                HandleRunningInstance(p);
                return true;
            }
            return false;
        }


    }