如何在 Swift 中将字符串更改为日期而不转换为任何时区？

Question

我知道这个简单的问题有很多问题，但我仍然无法得到清晰的想法。

这就是我想要的：

SelectedDateString = "19-08-2015 09:00 AM"
let dateFormatter = NSDateFormatter()
dateFormatter.dateFormat = "dd-MM-yyyy HH:mm a"
dateFormatter.timeZone = NSTimeZone();
let SelectedUTCDate = dateFormatter.dateFromString(SelectedDateString)!
println("SelectedLocalDate = \(SelectedLocalDate)") 
// OUTPUT: SelectedLocalDate = 2015-08-18 18:30:00 +0000

如果我不使用时区：

let dateFormatter = NSDateFormatter()
dateFormatter.dateFormat = "dd-MM-yyyy HH:mm a"
// dateFormatter.timeZone = NSTimeZone();
let SelectedUTCDate = dateFormatter.dateFromString(SelectedDateString)!
println("SelectedLocalDate = \(SelectedLocalDate)")
//OUTPUT: SelectedLocalDate = 2015-08-18 19:26:00 +0000

为什么时间和日期有变化？我想要的是：

//OUTPUT: SelectedLocalDate = 2015-08-19 09:00:00 +0000

我还想将本地日期转换为精确的 UTC 日期

//Like this: SelectedUTCDate = 2015-08-19 03:30:00 

inputString = "19-08-2015 10:45 am"  // My localtime is 10:35 AM, so I set 10 mins from now
 var currentUTCTime = NSDate() // currentUTCTime is 05: 15 AM. 

我想将 inputString 转换为其各自的 UTC 时间，并找出日期和字符串中两个时间之间的差异。

//Like this Date: diffInDate: 00-00-0000 00:10 and
// Like this String: diffInString: 10 mins

我怎样才能同时获得这两个？

Answer 1

let dateString = "19-08-2015 09:00 AM"
let dateFormatter = DateFormatter()
dateFormatter.calendar = Calendar(identifier: .iso8601)
dateFormatter.locale = Locale(identifier: "en_US_POSIX")
dateFormatter.timeZone = TimeZone(secondsFromGMT: 0)
dateFormatter.dateFormat = "dd-MM-yyyy hh:mm a"
if let dateFromString = dateFormatter.date(from: dateString) {
    print(dateFromString)   // "2015-08-19 09:00:00 +0000"
    dateFormatter.timeZone = .current
    dateFormatter.dateFormat = "dd-MM-yyyy hh:mm a Z"
    dateFormatter.string(from: dateFromString)  // 19-08-2015 06:00 AM -0300"
}

Answer 2

extension Date {
    func originToString(dateFormat: String) -> String {
        let dateFormatter = DateFormatter()
        dateFormatter.dateFormat = dateFormat
        dateFormatter.calendar = Calendar(identifier: .iso8601)
        dateFormatter.locale = Locale(identifier: "en_US_POSIX")
        dateFormatter.timeZone = TimeZone(secondsFromGMT: 0)
        return dateFormatter.string(from: self)
    }
}