How to convert this string in a date with this format? - swift

Question

Im working with a API, when I ask for a date, this API get my a String like this:
20190717-0300
I want to show that date in a UILabel with this format: "dd '\(preposition)' MMMM"
My attempt was to make a string extension:
extension String {
var toDate: String? {
let dateFormatter = DateFormatter()
let preposition = NSLocalizedString("of", comment: "Preposition of dates formatted")
dateFormatter.dateFormat = "dd '\(preposition)' MMMM"
dateFormatter.locale = Locale.current
if let date = dateFormatter.date(from: self) {
let dateString = dateFormatter.string(from: date)
return dateString
}
return nil
}
}
And then use it:
myLabel.text = thatString.toDate
But .toDate always return nil
Note: The answers I found on the site are cases with ISO format strings.
Expected result:
17 of July

Answer 1

Basically you need an input date format and an output date format.
extension String {
var toDate: String? {
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyyMMddZ"
if let date = dateFormatter.date(from: self) {
let preposition = NSLocalizedString("of", comment: "Preposition of dates formatted")
dateFormatter.dateFormat = "dd '\(preposition)' MMMM"
let dateString = dateFormatter.string(from: date)
return dateString
}
return nil
}
}
I totally agree with rmaddy's comment to use setLocalizedDateFormatFromTemplate
The source of the date field symbols is unicode.org: Date Format Patterns

Answer 2

Turn this into extension if you like:
// function
func formatDate(_ from:String, preposition:String) -> String? {
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyyMMddZ"
guard let date = dateFormatter.date(from: from) else {
return nil
}
dateFormatter.dateFormat = "dd '\(preposition)' MMMM"
return dateFormatter.string(from: date)
}
// example usage
let str = "20190717-0300"
if let formatted = formatDate(str, preposition: "of") {
print(formatted)
}