static class Program{  /// <summary>  /// 應用程序的主入口點。  /// </summary>  [STAThread]  static void Main()  {    Application.EnableVisualStyles();    Application.SetCompatibleTextRenderingDefault(false);    //1.這里判定是否已經有實例在運行    //只運行一個實例    Process instance = RunningInstance();    if (instance == null)    {      //1.1 沒有實例在運行      Application.Run(new frmMain());    }    else    {      //1.2 已經有一個實例在運行      HandleRunningInstance(instance);    }    //Application.Run(new frmMain());  }  //2.在進程中查找是否已經有實例在運行  #region 確保程序只運行一個實例  private static Process RunningInstance()  {    Process current = Process.GetCurrentProcess();    Process[] processes = Process.GetProcessesByName(current.ProcessName);    //遍歷與當前進程名稱相同的進程列表     foreach (Process process in processes)    {      //如果實例已經存在則忽略當前進程       if (process.Id != current.Id)      {        //保證要打開的進程同已經存在的進程來自同一文件路徑        if (Assembly.GetExecutingAssembly().Location.Replace("/", "http://") == current.MainModule.FileName)        {          //返回已經存在的進程          return process;        }      }    }    return null;  }  //3.已經有了就把它激活，并將其窗口放置最前端  private static void HandleRunningInstance(Process instance)  {    ShowWindowAsync(instance.MainWindowHandle, 1); //調用api函數，正常顯示窗口    SetForegroundWindow(instance.MainWindowHandle); //將窗口放置最前端  }  [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}