iOS Date() returns 不正确的值

Question

我正在使用以下代码获取 iOS 设备日期。

    let today = Date()
    let dateFormatter = DateFormatter()
    dateFormatter.dateFormat = "dd"
    let currentDate = dateFormatter.string(from: today)
    print("todayDate : \(currentDate)")
    dateFormatter.dateFormat = "MM"
    let currentMonth = dateFormatter.string(from: today)
    print("currentMonth : \(currentMonth)")
    dateFormatter.dateFormat = "YYYY"
    let currentYear = dateFormatter.string(from: today)
    print("currentYear : \(currentYear)")

当我在 iPhone 设置 29-12-2019 或 30-12-2019 或 31-12-2019 中更改设备日期时。 currentMonth 和 currentDate 值是正确的。但是，currentYear return 值是 2020 而不是 2019。请建议我解决这个问题。

Answer 1

A common mistake is to use YYYY. yyyy specifies the calendar year whereas YYYY specifies the year (of “Week of Year”), used in the ISO year-week calendar. In most cases, yyyy and YYYY yield the same number, however they may be different. Typically you should use the calendar year. see this for help : Challenges of DateFormatters

使用你的日期格式

"yyyy" is ordinary calendar year.

dateFormatter.dateFormat = "yyyy"

而不是

"YYYY" is week-based calendar year.

dateFormatter.dateFormat = "YYYY"

最后根据你的问题，

   let today = Date()
   let dateFormatter = DateFormatter()     
   dateFormatter.dateFormat = "yyyy"
   let currentYear = dateFormatter.string(from: today)
   print("currentYear : \(currentYear)")

你得到的输出是

iOS Date() returns 不正确的值

iOS Date() returns incorrect value

nsdateformatter

ios

swift