把请求下来的时间字符串(requestDateString)转换为NSDate
Swift2.3:
//创建formatter
let formatter = NSDateFormatter()
//设置时间格式
formatter.dateFormat = "EEE MMM d HH:mm:ss Z yyyy"
//设置时间区域
formatter.locale = NSLocale(localeIdentifier: "en")
//转换为字符串
let requestDate = formatter.dateFromString(requestDateString)
Swift3.0:
let requestDateString =