Why date formatter crashes?

问题:

My below code is working fine. I don't know why it crashes sometimes(Mostly on application launch. 1 case out of ~100).

extension Formatter {
    static let enUSPOSIX: DateFormatter = {
        let formatter = DateFormatter()
        formatter.locale = Locale(identifier: "en_US_POSIX")//
        return formatter
    }()
}


let dateFormatter = Formatter.enUSPOSIX
dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss+hh:mm"
let date = dateFormatter.date(from: "2018-05-13T00:00:00+05:30")
dateFormatter.timeZone = TimeZone(identifier: "UTC")
let calendar = Calendar.current
let dayComponent = calendar.component(.year, from: date!)//crashes here sometime
print(dayComponent)

回答1:

Basically your date format is wrong. The time zone +05:30 is ZZZZZ not +hh:mm, please read unicode.org Date Format Patterns

 dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ssZZZZZ"

Edit:

For this standard ISO8601 format I'd prefer ISO8601DateFormatter

let dateFormatter = ISO8601DateFormatter()
let date = dateFormatter.date(from: "2018-05-13T00:00:00+05:30")

回答2:

I had the same issue when testing on one of my applications

let dateFormatter = Formatter.enUSPOSIX
dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss+hh:mm"
let date = dateFormatter.date(from: "2018-05-13T00:00:00+05:30")
dateFormatter.timeZone = TimeZone(identifier: "UTC")
let calendar = Calendar.current
let dayComponent = calendar.component(.year, from: date!)

This is Crashing because the date object is nil so when fore unwrapping the date in dayComponent line this crashes. try this

let dateFormatter = Formatter.enUSPOSIX
dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss+hh:mm"
if let date = dateFormatter.date(from: "2018-05-13T00:00:00+05:30"){
   dateFormatter.timeZone = TimeZone(identifier: "UTC")
   let calendar = Calendar.current
   let dayComponent = calendar.component(.year, from: date!)
}else{
  dateFormatter.dateFormat = "yyyy-MM-dd'T'hh:mm:ss+hh:mm" // Date as 12 hour  
 if let date = dateFormatter.date(from: "2018-05-13T00:00:00+05:30"){
   dateFormatter.timeZone = TimeZone(identifier: "UTC")
  let calendar = Calendar.current
  let dayComponent = calendar.component(.year, from: date!)
} else{
   print("Cannot format Date")
 }
}

回答3:

Today I met exactly the same problem. Application randomly crashes on production because of force unwrapping on open func date(from string: String) -> Date?

My code looked like this:

let creationDate: Date = {
    let dateFormatter = DateFormatter()
    return dateFormatter.date(from: "19-06-2018 14:00")!
}()

After my investigation I realized that crashes appear only on devices which have set 12h date format in device settings. In these cases 14:00 does not exist because it should be "2:00PM".

Simply change in code fix that problem:

let creationDate: Date = {
    let dateFormatter = DateFormatter()
    dateFormatter.dateFormat = "dd-MM-yyyy HH:mm"
    dateFormatter.locale = Locale(identifier: "en_US_POSIX")

    return dateFormatter.date(from: "19-06-2018 14:00")!
}()