Converting total minutes to "HH:mm" format - swift

Question

I'm currently saving some timestamped data in the minutes format, eg 550 is 9:10AM.
Is there a way to convert this into the string "09:10"? I'll be using 24hr format.
I'm using swift for an iOS app, but if there is logic that's non-language specific, that would be helpful too.
Cheers,
Josh

Answer 1

The question is what the 550 really represents:
If it represents an abstract time interval, measured in minutes, you would likely convert it to a TimeInterval and then use DateComponentsFormatter to prepare a string representation of hours and minutes:
let timeInterval = TimeInterval(minutes * 60)
let formatter = DateComponentsFormatter()
formatter.allowedUnits = [.hour, .minute]
formatter.unitsStyle = .positional
formatter.zeroFormattingBehavior = .pad
let string = formatter.string(from: timeInterval)
This is a simple “hours and minutes” representation. This pattern is especially useful if the number of hours could exceed 24 (e.g. 1,550 minutes is 25 hours and 50 minutes, or 1 day, 1 hour, and 50 minutes, depending upon whether you add .day to allowedUnits or not).
If, however, you really mean that the 550 minutes is intended to literally represent the time of the day, then you might use calendrical date calculations and use DateFormatter for a string representation of the time:
let timeInterval = TimeInterval(minutes * 60)
let date = Calendar.current.startOfDay(for: Date()).addingTimeInterval(timeInterval)
let formatter = DateFormatter()
formatter.locale = Locale(identifier: "en_US_POSIX")
formatter.dateFormat = "HH:mm"
let string = formatter.string(from: date)
But, that having been said, if this really represented 9:10am in the morning (not an abstract time interval nine hours and ten minutes) and you wanted to show it in the UI, you would generally honor the device’s preferred time format (am/pm or 24-hour clock):
let timeInterval = TimeInterval(minutes * 60)
let date = Calendar.current.startOfDay(for: Date()).addingTimeInterval(timeInterval)
let formatter = DateFormatter()
formatter.timeStyle = .short
formatter.dateStyle = .none
let string = formatter.string(from: date)
Either way (forcing 24 hour clock or honor the user’s preferences), though, you really are displaying a time of day, which means that this while it will be 9:10am most days of the year, if you do this on the day that we spring forward to daylight savings, it will say 10:10am, but if on the day we fall backwards back to standard time on that day, it would be 8:10am.
Clearly, the syntax is different in Objective-C than it is in Swift, but the basic API is the same (though you obviously would be using the NS prefixes, e.g. NSDateComponentsFormatter and/or NSDateFormatter).