C#只允许启动一个WinFrom进程

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
[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;