Swift 3 - UTC 到时间前标签，考虑 12 小时 / 24 小时设备时间变化

Question

我想将时间UTC 转换为“5 秒前”。以前的标签也在考虑手机上的 12h / 24h 变化。因为会崩溃。现在下面的代码行返回标签值我想要在 Playground 中。但不在我的 ios 项目中。它不会进入 If 块。我错过了什么或有什么问题？

    let dateStringUTC = "2016-10-22 12:37:48 +0000"
    let dateFormatter = DateFormatter()
    dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss ZZZ"

    if let from = dateFormatter.date(from: dateStringUTC) {

        dateFormatter.dateFormat = "MMM d, yyyy h:mm:ss a"
        let stringFromDate = dateFormatter.string(from: from)
        let dateLast = dateFormatter.date(from: stringFromDate)

        let now = Date()
        let components: NSCalendar.Unit = [.second, .minute, .hour, .day, .weekOfMonth]
        let difference = (Calendar.current as NSCalendar).components(components, from: dateLast!, to: now, options: [])

        if difference.second! <= 0 {
            self.timeInfoLbl.text = "now"
        }
        if difference.second! > 0 && difference.minute! == 0 {
            self.timeInfoLbl.text = String(describing: difference.second!) + "s."
        }
        if difference.minute! > 0 && difference.hour! == 0 {
            self.timeInfoLbl.text = String(describing: difference.minute!) + "m."
        }
        if difference.hour! > 0 && difference.day! == 0 {
            self.timeInfoLbl.text = String(describing: difference.hour!) + "h."
        }
        if difference.day! > 0 && difference.weekOfMonth! == 0 {
            self.timeInfoLbl.text = String(describing: difference.day!) + "d."
        }
        if difference.weekOfMonth! > 0 {
            self.timeInfoLbl.text = String(describing: difference.weekOfMonth!) + "w."

            if difference.weekOfMonth! > 52 {
                let number = Float(difference.weekOfMonth!) / 52
                let strYear = String(format:"%.1f", number)
                self.timeInfoLbl.text = strYear + " year"
            }
        }
    }

Answer 1

要将此字符串转换为日期，我会这样做：

let dateStringUTC = "2016-10-22 12:37:48 +0000"
let dateFormatter = DateFormatter()
dateFormatter.locale = Locale(identifier: "en_US_POSIX")
dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss X"
let date = dateFormatter.date(from: dateStringUTC)!

然后，为了以良好的格式显示经过的时间，请考虑DateComponentsFormatter，例如：

let now = Date()

let formatter = DateComponentsFormatter()
formatter.unitsStyle = .full
formatter.maximumUnitCount = 2
let string = formatter.string(from: date, to: Date())! + " " + NSLocalizedString("ago", comment: "added after elapsed time to say how long before")