DateFormatter dateFromString Always Returns nil in swift 3

Question

Due to some reason fail to convert a string to a NSDate.

This is my date converting code:

 let kSQLiteDateFormat : String = "yyyy/MM/dd HH:mm:ss Z"
let dateFormat = [kSQLiteDateFormat,
"dd MM, yyyy",
"MMM-yyyy",
"yyyy-MM-dd",
"yyyy-12",
"yyyy/MM/dd",
"yyyy/mm/dd",
"yyyy-MM-dd HH:mm:ss",
"yyyy-MM-dd HH:mm:ss Z",
"yyyy-MM-dd HH:mm:ss K",
"yyyy-MM-dd HH:mm:ss ZZ",
"yyyy/MM/dd hh:mm a",
"MM/dd/yyyy",
"MM/dd/yyyy HH:mm:ss Z",
"h:mm a",
"hh:mm a",
"yyyy/MM/dd HH:mm:ss Z",
"yyyy/MM/dd h:mm a",
"MM/dd/yyyy h:mm a",
"yyyy-MM-dd h:mm a",
"yyyy-MM-dd'T'hh:mm:ss",
"yyyy/MM/dd h a",
"yyyy-MM-dd'T'HH:mm:ss","dd MMM, yyyy","dd-MM-yyyy HH:mm", "EEE, MMM dd","MM/dd/yyyy hh:mm:ss a"]


if let dateString : String = dateString as String? {
        let dateFormatter : DateFormatter = DateFormatter()
        for format in dateFormat {

            dateFormatter.dateFormat =  format
            if  let date : NSDate = (dateFormatter.date(from: dateString)! as NSDate) {
                return date
            }
        }
    }
    return nil

every time return nil

Answer 1

The forced unwrapping in

if  let date : NSDate = (dateFormatter.date(from: dateString)! as NSDate) {
    return date
}

makes the program crash if dateString does not match the date format and dateFormatter.date(from: dateString) returns nil.

What you probably want is

if let date = dateFormatter.date(from: dateString) {
    return date
}

or, if you really need an NSDate and not a Date:

if let date = dateFormatter.date(from: dateString) {
    return date as NSDate
}

In addition, you might want to set the formatter's locate to "POSIX"

dateFormatter.locale = Locale(identifier: "en_US_POSIX")

in order to avoid a dependency on the user's regional preferences, compare DateFormatter doesn't return date for "HH:mm:ss".