static class Program
{
  /// <summary>
  /// 应用程序的主入口点。
  /// </summary>
  [STAThread]
  static void Main()
  {
    Application.EnableVisualStyles();
    Application.SetCompatibleTextRenderingDefault(false);

    //1.这里判定是否已经有实例在运行
    //只运行一个实例
    Process instance = RunningInstance();
    if (instance == null)
    {
      //1.1 没有实例在运行
      Application.Run(new frmMain());
    }
    else
    {
      //1.2 已经有一个实例在运行
      HandleRunningInstance(instance);
    }

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

  //2.在进程中查找是否已经有实例在运行
  #region 确保程序只运行一个实例
  private static Process RunningInstance()
  {
    Process current = Process.GetCurrentProcess();
    Process[] processes = Process.GetProcessesByName(current.ProcessName);
    //遍历与当前进程名称相同的进程列表 
    foreach (Process process in processes)
    {
      //如果实例已经存在则忽略当前进程 
      if (process.Id != current.Id)
      {
        //保证要打开的进程同已经存在的进程来自同一文件路径
        if (Assembly.GetExecutingAssembly().Location.Replace(\"/\", \"\\\\\") == current.MainModule.FileName)
        {
          //返回已经存在的进程
          return process;
        }
      }
    }
    return null;
  }
  //3.已经有了就把它激活，并将其窗口放置最前端
  private static void HandleRunningInstance(Process instance)
  {
    ShowWindowAsync(instance.MainWindowHandle, 1); //调用api函数，正常显示窗口
    SetForegroundWindow(instance.MainWindowHandle); //将窗口放置最前端
  }
  [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
}