winform只运行一个实例

 static class Program
    {
        /// <summary>
        /// 应用程序的主入口点。
        /// </summary>
        [STAThread]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Process instance = RunningInstance();
            if (instance == null)
            {
                //1.1 没有实例在运行
                Application.Run(new Form1());
            }
            else
            {
                //1.2 已经有一个实例在运行
                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;
                    }
                }
            }
            return null;
        }


        private static void HandleRunningInstance(Process instance)
        {
            MessageBox.Show("已经在运行！", "提示信息", MessageBoxButtons.OK, MessageBoxIcon.Information);
            ShowWindowAsync(instance.MainWindowHandle, 1);  //调用api函数，正常显示窗口
            SetForegroundWindow(instance.MainWindowHandle); //将窗口放置最前端
        }
        [DllImport("User32.dll")]
        private static extern bool ShowWindowAsync(System.IntPtr hWnd, int cmdShow);
        [DllImport("User32.dll")]
        private static extern bool SetForegroundWindow(System.IntPtr hWnd);
    }