NSDateComponentsFormatter's stringFromDate(_, toDate:) returns nil

Question

Question

Why is string nil?

let formatter = NSDateComponentsFormatter()
let referenceDate = NSDate(timeIntervalSinceReferenceDate: 0)
let intervalDate = NSDate(timeInterval: 3628810, sinceDate: referenceDate)
let string = formatter.stringFromDate(referenceDate, toDate: intervalDate)

I'm expecting a string like "6w 10s" to be returned.

(6 weeks is 3,628,800 seconds.)

Attempted Troubleshooting

To troubleshoot, I tried setting allowedUnits:

formatter.allowedUnits = .YearCalendarUnit | .MonthCalendarUnit | .WeekCalendarUnit | .DayCalendarUnit | .HourCalendarUnit | .MinuteCalendarUnit | .SecondCalendarUnit

Which results in this error:

"NSInvalidArgumentException", "Specifying positional units with gaps is ambiguous, and therefore unsupported"

I don't know what a "positional unit" is (outside of football), and I don't think I'm specifying any gaps.

Notes

I'm not using stringFromTimeInterval() because that will return different results depending on the system's current date. (i.e., February only has 28/29 days in a month.) I want to calculate the time interval from the NSDate reference date.

I'm using Xcode 6.1.1 (6A2008a). Here's a Playground screenshot if that helps:

enter image description here

rintaro · Accepted Answer · 2015-02-20T17:59:08.607

From the headerdoc:

/* Bitmask of units to include. Set to 0 to get the default behavior.
   Note that, especially if the maximum number of units is low, unit
   collapsing is on, or zero dropping is on, not all allowed units may
   actually be used for a given NSDateComponents. Default value is the
   components of the passed-in NSDateComponents object, or years | 
   months | weeks | days | hours | minutes | seconds if passed an
   NSTimeInterval or pair of NSDates.

   Allowed units are:

    NSCalendarUnitYear
    NSCalendarUnitMonth
    NSCalendarUnitWeekOfMonth (used to mean "quantity of weeks")
    NSCalendarUnitDay
    NSCalendarUnitHour
    NSCalendarUnitMinute
    NSCalendarUnitSecond

   Specifying any other NSCalendarUnits will result in an exception.
 */
var allowedUnits: NSCalendarUnit

So:

let formatter = NSDateComponentsFormatter()
formatter.calendar = NSCalendar.currentCalendar()
formatter.allowedUnits = nil
formatter.allowedUnits |= .CalendarUnitYear
formatter.allowedUnits |= .CalendarUnitMonth
formatter.allowedUnits |= .CalendarUnitWeekOfMonth
formatter.allowedUnits |= .CalendarUnitDay
formatter.allowedUnits |= .CalendarUnitHour
formatter.allowedUnits |= .CalendarUnitMinute
formatter.allowedUnits |= .CalendarUnitSecond

let referenceDate = NSDate(timeIntervalSinceReferenceDate: 0)
let intervalDate = NSDate(timeInterval: 214458810, sinceDate: referenceDate)
let string = formatter.stringFromDate(referenceDate, toDate: intervalDate)
// -> "6y 9m 2w 4d 3:53:30"

When we omit one of them in the middle:

formatter.allowedUnits = nil
formatter.allowedUnits |= .CalendarUnitYear
formatter.allowedUnits |= .CalendarUnitMonth
formatter.allowedUnits |= .CalendarUnitWeekOfMonth
formatter.allowedUnits |= .CalendarUnitDay
// formatter.allowedUnits |= .CalendarUnitHour
formatter.allowedUnits |= .CalendarUnitMinute
formatter.allowedUnits |= .CalendarUnitSecond

'Specifying positional units with gaps is ambiguous, and therefore unsupported' error :) That is the "gap" means, I think.

Ah, so it's `.WeekOfMonth`, not `.Week` — that sort of explains the "gaps" error. — Nate Cook, Feb 20 '15 at 17:54
Yeah, we can't use `.WeekCalendarUnit`, and ignored. That is the "gap" I think. — rintaro, Feb 20 '15 at 17:55
And there's also a bug, since it clearly isn't doing this: "Default value is ... years | months | weeks | days | hours | minutes | seconds if passed an NSTimeInterval or pair of NSDates." — Nate Cook, Feb 20 '15 at 17:56
on iOS 12 skipping `.weekOfMonth` causes this crash. this works: `formatter.allowedUnits = [.year, .month, .weekOfMonth, .day, .hour, .minute, .second]` — spnkr, Nov 10 '20 at 12:45

score 4 · Answer 2 · answered Feb 20 '15 at 17:19

4

This works for me to get rid of the "gaps":

formatter.allowedUnits = .DayCalendarUnit | .HourCalendarUnit | .MinuteCalendarUnit | .SecondCalendarUnit

answered Feb 20 '15 at 17:19

Nate Cook

92,417
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That doesn't return `nil` (it returns "42d 0:00:10"), but why can't I get the weeks / months / years? – Aaron Brager Feb 20 '15 at 17:26
`stringFromTimeInterval()` has no problem returning weeks / months / years using the current date as a start date. – Aaron Brager Feb 20 '15 at 17:27
I think it's an API bug - the docs talk about a default set of allowed units, so it shouldn't just be returning `nil` from that unconfigured call. – Nate Cook Feb 20 '15 at 17:42

trndjc · Answer 3 · 2020-02-03T16:28:25.303

3

Not specifying a unit style will cause this in Swift 4 and 5.

let componentsFormatter = DateComponentsFormatter()
componentsFormatter.unitsStyle = .full

Other unit styles: .spellOut, .short, .brief, .abbreviated, .positional

edited Feb 03 '20 at 16:28

answered Nov 27 '18 at 22:15

trndjc

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MRizwan33 · Answer 4 · 2018-04-18T05:30:29.383

Swift 3.0 version for Solving this.

 let dateFormatted = DateComponentsFormatter()

 dateFormatted.allowedUnits = [NSCalendar.Unit.year, NSCalendar.Unit.month, NSCalendar.Unit.weekOfMonth ,NSCalendar.Unit.day, NSCalendar.Unit.hour, NSCalendar.Unit.minute, NSCalendar.Unit.second]

 let autoFormattedDifference = dateFormatted.string(from: currentDate, to: dateFromTimestamp)

 print("The difference between dates is: \(autoFormattedDifference!)")

Now here the difference is giving all the value of allowUnits from ascending or descending order.

NSDateComponentsFormatter's stringFromDate(_, toDate:) returns nil

Question

Attempted Troubleshooting

Notes

4 Answers4

Linked