字符串中的Swift日期始终返回nil

Question

I have a date that is a string that looks like this:

Apr 25 2018 12:00AM

What I am trying to do is convert this date format to yyyy-MM-dd and then convert it back to a string, I have a tried the following:

let formatter = DateFormatter()
            formatter.dateFormat = "M dd yyyy h:mm A"
            let SLAIssuedFinalGradingDate = formatter.date(from: tableDic["SLAIssuedFinalGradingDate"] as! String)
            formatter.dateFormat = "yyyy-MM-dd"
            let SLAIssuedFinalGradingDateString = formatter.string(from: SLAIssuedFinalGradingDate!)

But SLAIssuedFinalGradingDate always returns nil, what am I doing wrong?

Answer 1

Your dateFormat for Apr 25 2018 12:00AM is not right. You are using M dd yyyy h:mm A , but format would be MMM dd yyyy hh:mma .
Use this link to check date format .

Code Should be:

let formatter = DateFormatter()
formatter.locale =  Locale(identifier: "en_US_POSIX")
formatter.dateFormat = "MMM dd yyyy hh:mma"
let SLAIssuedFinalGradingDate = formatter.date(from: tableDic["SLAIssuedFinalGradingDate"] as! String)
formatter.dateFormat = "yyyy-MM-dd"
let SLAIssuedFinalGradingDateString = formatter.string(from: SLAIssuedFinalGradingDate!)

Answer 2

Your dateFormat string is incorrect. A DateFormatter will always return nil if the dateFormat string does not match the supplied string.

"MMM dd yyyy hh:mma"

This is what you're after. I suggest you review a DateFormatter cheat sheet and familiarise yourself with the symbols.