C WinForm Judge whether the program is already running and only one instance is allowed to run with source code

When we develop WinFrom program, we often hope that only one instance of the program is running, so as to avoid running multiple identical programs. 1 is meaningless and 2 is error-prone.

In order to be more convenient to use, the author sorted out a piece of code for his own use, which can judge whether the program is running, only one instance is running, and when the program is running, double-click the program icon and call out the running program directly.

Look at the code below, just add the following code in the entry file of the program:

static class Program
{
  /// <summary>
  ///  The main entry point for the application. 
  /// </summary>
  [STAThread]
  static void Main()
  {
    Application.EnableVisualStyles();
    Application.SetCompatibleTextRenderingDefault(false);

    //1. It is determined here whether an instance is already running 
    // Run only 1 Instances 
    Process instance = RunningInstance();
    if (instance == null)
    {
      //1.1  There are no instances running 
      Application.Run(new frmMain());
    }
    else
    {
      //1.2  There are already 1 Instances are running 
      HandleRunningInstance(instance);
    }

    //Application.Run(new frmMain());
  }

  //2. Find out whether an instance is already running in the process 
  #region  Ensure that the program only runs 1 Instances 
  private static Process RunningInstance()
  {
    Process current = Process.GetCurrentProcess();
    Process[] processes = Process.GetProcessesByName(current.ProcessName);
    // Traverse the list of processes with the same name as the current process  
    foreach (Process process in processes)
    {
      // Ignore the current process if the instance already exists  
      if (process.Id != current.Id)
      {
        // Ensure that the process to be opened comes from the same process as the existing process 1 File path 
        if (Assembly.GetExecutingAssembly().Location.Replace("/", "\\") == current.MainModule.FileName)
        {
          // Returns an existing process 
          return process;
        }
      }
    }
    return null;
  }
  //3. If you already have it, activate it and place its window at the front 
  private static void HandleRunningInstance(Process instance)
  {
    ShowWindowAsync(instance.MainWindowHandle, 1); // Call api Function to display the window normally 
    SetForegroundWindow(instance.MainWindowHandle); // Place the window at the front 
  }
  [DllImport("User32.dll")]
  private static extern bool ShowWindowAsync(System.IntPtr hWnd, int cmdShow);
  [DllImport("User32.dll")]
  private static extern bool SetForegroundWindow(System.IntPtr hWnd);
  #endregion
}