C#只允许启动一个WinFrom进程

    [STAThread]
    public static void Main()
    {
        //Get the running instance.
        Process instance = RunningInstance();
        if (instance == null)
        {
            System.Windows.Forms.Application.EnableVisualStyles(); //这两行实现 XP 可视风格
            System.Windows.Forms.Application.DoEvents();
            //There isn't another instance, show our form.
            Application.Run(new Main());
        }
        else
        {
            //There is another instance of this process.
            HandleRunningInstance(instance);
        }
    }
    public static Process RunningInstance()
    {
        Process current = Process.GetCurrentProcess();
        Process[] processes = Process.GetProcessesByName(current.ProcessName);
        //Loop through the running processes in with the same name
        foreach (Process process in processes)
        {
            //Ignore the current process
            if (process.Id != current.Id)
            {
                //Make sure that the process is running from the exe file.
                if (Assembly.GetExecutingAssembly().Location.Replace("/", "\\") == current.MainModule.FileName)
                {
                    //Return the other process instance.
                    return process;
                }
            }
        }
        //No other instance was found, return null.
        return null;
    }
    public static void HandleRunningInstance(Process instance)
    {
        //Make sure the window is not minimized or maximized
        ShowWindowAsync(instance.MainWindowHandle, WS_SHOWNORMAL);
        //Set the real intance to foreground window
        SetForegroundWindow(instance.MainWindowHandle);
    }
    [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;

方法一：只禁止多个进程运行

    [STAThread]
    public static void Main()
    {
        bool ret;
        System.Threading.Mutex mutex = new System.Threading.Mutex(true, Application.ProductName, out ret);
        if (ret)
        {
            System.Windows.Forms.Application.EnableVisualStyles(); //这两行实现 XP 可视风格
            System.Windows.Forms.Application.DoEvents();
            System.Windows.Forms.Application.Run(new Main());
            // Main 为你程序的主窗体，如果是控制台程序不用这句
            mutex.ReleaseMutex();
        }
        else
        {
            MessageBox.Show(null, "有一个和本程序相同的应用程序已经在运行，请不要同时运行多个本程序。\n\n这个程序即将退出。", Application.ProductName, MessageBoxButtons.OK, MessageBoxIcon.Warning);
            // 提示信息，可以删除。
            Application.Exit();//退出程序
        }
    }

方法二：禁止多个进程运行,并当重复运行时激活以前的进程