Swift -新的更新给出了可选的问题

Question

我刚刚在我的iOS项目上更新到Xcode 8和Swift 3。它现在给我的应用程序带来了问题。而不是给我正确的日期和时间元素，我的标签显示"Optional(2016)/Optional(09)/Optional(15)"而不是"2016/09/15"。自更新以来我没有更改任何代码，以前是正确的。这就是我使用的:

let date = Date()
let calendar = Calendar.current
let components = (calendar as NSCalendar).components([.month, .year, .day, .hour, .minute, .second], from: date)
var day = components.day
var day1 = components.day
var year = components.year
var month = components.month
let hour = components.hour
let minutes = components.minute
let seconds = components.second

let timeString = "(hour):(minutes):(seconds)"
var dateString = "(year)/(month)/(day)"

谁知道新的可选语法?

Answer 1

DateComponents的所有属性都变成了可选项，例如

var day: Int? { get set }

但是您可以安全地展开在components变量中指定的所有属性。

var day = components.day!

Answer 2

如果你想用前导零来格式化它，最简单的方法可能是使用DateFormatter:

let date = Date()
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy/MM/dd"
let dateString = dateFormatter.string(from: date)
let timeFormatter = DateFormatter()
timeFormatter.dateFormat = "HH:mm:ss"
let timeString = timeFormatter.string(from: date)

---

如果你真的想自己构建这些字符串，使用String(format:):

let calendar = Calendar.current
let components = calendar.dateComponents([.month, .year, .day, .hour, .minute, .second], from: date)
let day = components.day
let year = components.year
let month = components.month
let hour = components.hour
let minutes = components.minute
let seconds = components.second
let timeString = String(format: "%02d:%02d:%02d", hour!, minutes!, seconds!)
let dateString = String(format: "%04d/%02d/%02d", year!, month!, day!)

Answer 3

在创建timeString和dateString时，您需要使用!展开变量:

let timeString = "(hour!):(minutes!):(seconds!)"
var dateString = "(year!)/(month!)/(day!)"
print(timeString)
print(dateString)

将打印出:

6:0:25
2016/9/16