C#中事件的定义和使用

            public event FileWatchEventHandler FileWatchEvent;

            protected virtual void OnFileChange(EventArgs e)
            {
                  if (FileWatchEvent != null)
                  {
                       
                        FileWatchEvent(this, e);
                  }
            }

            public void MonitorFile()
            {
                  bool bCurrentStatus;

                  while(true)
                  {
                        bCurrentStatus = File.Exists("test.txt");

                        //状态不符，说明文件被删除或重新创建，此时触发事件；
                        if ( bCurrentStatus != _bLastStatus )
                        {
                              _bLastStatus = bCurrentStatus;
                              OnFileChange( EventArgs.Empty );