static class Program
{
  /// <summary>
  /// 應(yīng)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(jīng)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(jīng)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(jīng)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(jīng)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(jīng)存在的進程來自同一文件路徑
        if (Assembly.GetExecutingAssembly().Location.Replace("/", "\\") == current.MainModule.FileName)
        {
          //返回已經(jīng)存在的進程
          return process;
        }
      }
    }
    return null;
  }
  //3.已經(jīng)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(diào)用api函數(shù)，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
}