时间戳和字符串之间转换 Swift

    //时间戳转成字符串
    func timeIntervalChangetoTimeStr(timeInterval:TimeInterval, dateFormat:String?) -> String {
        let date:NSDate = NSDate.init(timeIntervalSince1970: timeInterval/1000)
        let formatter = DateFormatter.init()
        if dateFormat == nil {
            formatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
        }else{
            formatter.dateFormat = dateFormat
        }
        return formatter.string(from: date as Date)
    }

    //字符串转时间戳
    func timeStrChangetotimeInterval(timeStr: String?, dateFormat:String?) -> String {
        if timeStr?.count ?? 0 > 0 {
            return ""
        }
        let format = DateFormatter.init()
        format.dateStyle = .medium
        format.timeStyle = .short
        if dateFormat == nil {
            format.dateFormat = "yyyy-MM-dd HH:mm:ss"
        }else{
            format.dateFormat = dateFormat
        }
        let date = format.date(from: timeStr!)
        return String(date!.timeIntervalSince1970)
    }