如何只能运行一个程序

怎么只能运行一个程序
如何做到只能运行一个程序？并且在第二次打开程序的时候将第一次打开的程序窗口激活

我做的是个TXT编辑器

我想如果我直接打开一个文本文件（之前已经打开一个程序了）但是这个文本文件是在第一次打开的程序窗口中显示的

怎么弄啊？

[解决办法]
同时只有一个窗体实例，再次打开激活已打开窗体的范例
[解决办法]

C# code

        [DllImport("User32.dll")]        private static extern bool ShowWindowAsync(IntPtr hWnd, int cmdShow);        [DllImport("User32.dll")]        private static extern bool SetForegroundWindow(IntPtr hWnd);        [DllImport("User32.dll", EntryPoint = "FindWindow")]        private extern static IntPtr FindWindow(string lpClassName, string lpWindowName);        //添加api        //获取当前运行的实例        public static Process GetRunningInstance()        {            Process current = Process.GetCurrentProcess();            Process[] processes = Process.GetProcessesByName(current.ProcessName);            foreach (Process process in processes)            {                if (process.Id != current.Id)                    if (Assembly.GetExecutingAssembly().Location.Replace("/", "\\") == current.MainModule.FileName)                        return process;            }            return null;        }        public static void HandleRunningInstance(Process instance)        {            if (instance != null && instance.MainWindowHandle.ToInt32() != 0)            {                string windowTile = instance.MainWindowTitle.Trim();                if (windowTile == "系统标题")                    ShowWindowAsync(instance.MainWindowHandle, 3);                else                    ShowWindowAsync(instance.MainWindowHandle, 1);                SetForegroundWindow(instance.MainWindowHandle);            }            else            {                IntPtr hwnd = FindWindow(null, "系统标题");                if (hwnd.ToInt32() == 0)                {                    hwnd = FindWindow(null, "系统标题");                    ShowWindowAsync(hwnd, 1);                    SetForegroundWindow(hwnd);                }                else                {                    ShowWindowAsync(hwnd, 3);                    SetForegroundWindow(hwnd);                }            }        }
[解决办法]
http://topic.csdn.net/u/20091118/18/9f3f7c0a-20fa-4006-9ccd-823734b10353.html