public static System.Diagnostics.Process RunningInstance()        {            System.Diagnostics.Process current = System.Diagnostics.Process.GetCurrentProcess();            System.Diagnostics.Process[] processes = System.Diagnostics.Process.GetProcessesByName(current.ProcessName);            //查找相同名称的进程            foreach (System.Diagnostics.Process process in processes)            {                //忽略当前进程                if (process.Id != current.Id)                {                    //确认相同进程的程序运行位置是否一样.                    if (System.Reflection.Assembly.GetExecutingAssembly().Location.Replace("/", "\\") == current.MainModule.FileName)                    {                        //Return the other process instance.                        return process;                    }                }            }            //No other instance was found, return null.            return null;        }

在main中调用

Application.EnableVisualStyles();            Application.SetCompatibleTextRenderingDefault(false);            System.Diagnostics.Process instance = RunningInstance();            if (instance == null)            {                Application.Run(new Form1());            }            else            {                MessageBox.Show("已有程序打开");            }