从 TimeZone.abbreviation() 初始化 TimeZone 时遇到问题

Question

I am storing user birth dates on my backend via storing a date component dictionary. It looks something like this:

{
    "day": 1,
    "month": 1,
    "year": 1970,
    "timeZone": "GMT"
}

To store this object, it grabs the user's birth day, month, and year from user input. The user time zone, however, is gathered via TimeZone.current.abbreviation() .

Now, some of my user birthdate objects on my backend have their "timeZone" formatted as "CST" , "BST" , or "PDT" . "timeZone" s that are formatted this way successfully initialize a TimeZone on the front end via let timeZone = TimeZone(abbreviation: "CST")! , let timeZone = TimeZone(abbreviation: "BST")! , or let timeZone = TimeZone(abbreviation: "PDT")! , respectively.

The problem is, other user birthdate objects on my backend have their "timeZone" formatted as "GMT+8" . When trying to initialize "timeZone" s formatted like this via let timeZone = TimeZone(abbreviation: "GMT+8")! , the initialization returns nil . I also tried let timeZone = TimeZone(identifier: "GMT+8")! , but this returns nil as well.

Is there a way to initialize a TimeZone when it is formatted with respect to its offset to GMT as opposed to its unique abbreviation? I've seen a TimeZone initializer that is TimeZone(secondsFromGMT: Int) . Could I simply take the 8 from "GMT+8" and multiply it by 3600 (the number of seconds in an hour) and pass this result to TimeZone(secondsFromGMT: Int) ?

Answer 1

I ended up writing code that adapts my application to account for these unexpected fringe cases where a TimeZone's abbreviation is formatted like "GMT+8" rather than "SGT" . I created an extension to TimeZone :

extension TimeZone {
    static func timeZone(from string: String) -> TimeZone {
        //The string format passed into this function should always be similar to "GMT+8" or "GMT-3:30"

        if string.contains("±") {
            //This case should always be "GMT±00:00", or simply GMT
            return TimeZone(secondsFromGMT: 0)!
        } else {

            //If the string doesn't contain "±", then there should be some offset. We will split the string into timeZone components. "GMT+8" would split into ["GMT", "8"]. "GMT-3:30" would split int ["GMT","3","30"]
            let timeZoneComponents = string.components(separatedBy: CharacterSet(charactersIn: "+-:"))
            var isAheadOfGMT: Bool!

            //Check if the string contains "+". This will dictate if we add or subtract seconds from GMT
            if string.contains("+") {
                isAheadOfGMT = true
            } else {
                isAheadOfGMT = false
            }

            //Grab the second element in timeZoneElements. This represents the offset in hours
            let offsetInHours = Int(timeZoneComponents[1])!

            //Convert these hours into seconds
            var offsetInSeconds: Int!
            if isAheadOfGMT {
                offsetInSeconds = offsetInHours * 3600
            } else {
                offsetInSeconds = offsetInHours * -3600
            }

            //Check if there is a colon in the passed string. If it does, then there are additional minutes we need to account for
            if string.contains(":") {
                let additionalMinutes = Int(timeZoneComponents[2])!
                let additionalSeconds = additionalMinutes * 60
                offsetInSeconds += additionalSeconds
            }

            //Create a TimeZone from this calculated offset in seconds
            let timeZoneFromOffset = TimeZone(secondsFromGMT: offsetInSeconds)!

            //Return this value
            return timeZoneFromOffset
        }
    }
}

It is used like so:

let json: [String:String] = ["timeZone":"GMT+8"]
let timeZone = json["timeZone"]
let birthDate: BirthDate!
if let timeZoneFromAbbrev = TimeZone(abbreviation: timeZone) {
    birthDate = BirthDate(day: birthDay, month: birthMonth, year: birthYear, timeZone: timeZoneFromAbbrev)
} else {       
    let timeZoneFromOffset = TimeZone.timeZone(from: timeZone)
    print(timeZoneFromOffset.abbreviation())
    //Prints "GMT+8"

    birthDate = BirthDate(day: birthDay, month: birthMonth, year: birthYear, timeZone: timeZoneFromOffset)
}

My BirthDate class for context:

class BirthDate {
    var day: Int
    var month: Int
    var year: Int
    var timeZone: TimeZone

    init(day: Int, month: Int, year: Int, timeZone: TimeZone) {
        self.day = day
        self.month = month
        self.year = year
        self.timeZone = timeZone
    }
}

Time zones are funny things to work with. If anybody sees issue with the TimeZone extension above, please let me know. I think I've accounted for all scenarios, but could be mistaken.