swift - What am I doing wrong with NSDateComponentsFormatter? -

i found out new-to-ios8 class nsdatecomponentsformatter, lets format time intervals rather dates. cool. i've written code more times care think about. decided try , use in playground, can't work. here's (swift) code:

var componentsformatter = nsdatecomponentsformatter() componentsformatter.allowedunits =   .calendarunithour |   .calendarunitminute |   .calendarunitsecond  componentsformatter.unitsstyle = .positional  let interval: nstimeinterval = 345.7  let intervalstring = componentsformatter.stringfromtimeinterval(interval)  println("interval string = \(intervalstring)") 

this displays

interval string = nil

i've tried various things, no joy. have working example using new class, or can spot i'm missing?

(i speak objective-c too, if have sample code in objective-c works well.)

swift 3.1 • xcode 8.3.2

extension formatter {     static let datecomponents: datecomponentsformatter = {         let formatter = datecomponentsformatter()         formatter.calendar = calendar(identifier: .iso8601)         formatter.unitsstyle = .full         formatter.includesapproximationphrase = true         formatter.includestimeremainingphrase = true         formatter.maximumunitcount = 2         formatter.zeroformattingbehavior = .default         formatter.allowsfractionalunits = false         formatter.allowedunits = [.year, .month, .weekofmonth, .day, .hour, .minute, .second]         return formatter     }() } extension timeinterval {     var remainingtime: string {         return formatter.datecomponents.string(from: self) ?? ""     } } 

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let interval = 60.0 * 60 * 24 * 7  let intervalstring = interval.remainingtime   //  "about 1 week remaining" 

---

positional time

extension formatter {     static let positional: datecomponentsformatter = {         let formatter = datecomponentsformatter()         formatter.unitsstyle = .positional         formatter.zeroformattingbehavior = .default         formatter.allowedunits = [.hour, .minute, .second]         return formatter     }()  } extension timeinterval {     var hourminutesecond: string {         return formatter.positional.string(from: self) ?? ""     } }  let time = 345.7  let positional = time.hourminutesecond   // "5:45"