Unable to parse a date on real device, works in simulator

Question

I have an app and if I try to run this app on real devices (iPhone 5S and 6) - Xcode shows error:

fatal error: unexpectedly found nil while unwrapping an Optional value 2017-04-11 00:43:58.724143+0200 APN[2153:475883] fatal error: unexpectedly found nil while unwrapping an Optional value

There is a block of code where is problem. But in simulator is all ok and correct.

let stringBefore = "Mon, 10 Apr 2017 11:39:24 +0000"

let startIndexDate = stringBefore.index(stringBefore.startIndex, offsetBy: 5)
let endIndexDate = stringBefore.index(stringBefore.endIndex, offsetBy: -15)

let rangeDate = startIndexDate..<endIndexDate
let stringAfter = stringBefore.substring(with: rangeDate)

let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "dd MMM yyyy"

let date = dateFormatter.date(from: stringAfter)
dateFormatter.dateFormat = "dd.MM.yyyy"

let finish = dateFormatter.string(from: date!) // there is the problem but why in Simulator is ok?

I know that I can write

dateFormat = "EEE, dd MMM yyyy hh:mm:ss +zzzz"

but I would like to ask you where is the problem?

Answer 1

It's possible it's a weird time zone issue that your converter isn't handling. I can't know without some debugging.

Regardless, I would recommend using another DateFormatter to find your date rather than trying to parse the string:

let startingFormatter = DateFormatter()
startingFormatter.dateFormat = "EEE, dd MMM y HH:mm:ss Z"

let endingFormatter = DateFormatter()
endingFormatter.dateFormat = "dd.MM.yyyy"

let stringBefore = "Mon, 10 Apr 2017 11:39:24 +0000"
let actualDate = startingFormatter.date(from: stringBefore)

if let actualDate = actualDate {
    let finish = endingFormatter.string(from: actualDate) //result is "10.04.2017"
}
else {
    //handle error
}

Also, as a general rule, force unwrapping an optional ( date! ) is a bad idea unless you're 100% confident there is a value, (which you can't be in this case because you don't know what's happening under the hood), or are ok with your program crashing if that value doesn't exist.