C# only allows two ways to start a WinFrom process

Method 1: Only prohibit multiple processes from running

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[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(); //These two lines implement XP visual style
System.Windows.Forms.Application.DoEvents();
System.Windows.Forms.Application.Run(new Main()) ; A // Main is the main window of your program. The program is already running, please do not run multiple programs at the same time. nnThis program is about to exit.
           Application.Exit();//Exit the program      
    }  
}
[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(); //These two lines implement XP visual style
System.Windows.Forms.Application.DoEvents();
         System.Windows.Forms.Application.Run(new Main());
                         //                                                              ‘ Main ’ is the main form of your program. If it is a console program, don’t use this sentence                                                                {
   MessageBox.Show(null, "An application identical to this program is already running. Please do not run multiple programs at the same time. nnThis program is about to exit.", Application.ProductName, MessageBoxButtons.OK, MessageBoxIcon.Warning) ;
                                                                             // Prompt information, can be deleted.
Application.Exit();//Exit the program
}
}


Method 2: Disable multiple processes from running, and activate the previous process when running repeatedly

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[STAThread]
public static void Main()
{
  //Get the running instance.
Process instance = RunningInstance();
if (instance == null)
{ System.Windows.Forms.Application.EnableVisualStyles(); //These two lines implement XP visual style
        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;  
[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; 

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