func isExpired(time:String) -> Bool {
      let dformatters = DateFormatter.init()
      dformatters.dateFormat = "yyyy-MM-dd HH:mm"
      let now = NSDate()
      //let dateString1 = "2017-07-06 13:40"
      let date1 = dformatters.date(from: time)
      //let dateString2 = "2017-07-06 13:41"
      //let date2 = dformatters.date(from: dateString2)
      
      if date1?.compare(now as Date) == ComparisonResult.orderedAscending {
          //print("date1 is earlier")
          return false
      } else if date1?.compare(now as Date) == ComparisonResult.orderedDescending {
          //print("date2 is earlier")
          return true
      } else if date1?.compare(now as Date) == ComparisonResult.orderedSame {
          //print("Same date!!!")
      }
      return true
  }

//調(diào)用此方法，傳入指定時間字符串，與當前時間對比，如果早于當前時間返回false，否則返回true