NSDateFormatter.dateFromString返回nil（“ yyyy-MM-dd”到NSDate）

Question

Having a problem with NSDateFormatter.

So I have a date string formatted "yyyy-MM-dd" , for example 2015-09-22. However when I pass this into NSDateFormatter.dateFromString, the method returns nil. My code is as follows:

let dateFormatter = NSDateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd"
dateFormatter.locale = NSLocale(localeIdentifier: "en_US_POSIX")
let dateAsNSDate = dateFormatter.dateFromString(payload.objectForKey("messageExpiry") as! String)

From the debugger console at a breakpoint just above this code:

po payload.objectForKey("messageExpiry") as! String

"2015-09-31"

I have explored other questions similar to this but am as of yet still unable to fix this problem. Any and all help would be appreciated.

Answer 1

Your code is correct and produces the expected result eg for the input string "2015-09-22". For the input "2015-09-31" however, nil is returned because that is an invalid date: September has only 30 days.

You can set

dateFormatter.lenient = true

and then "2015-09-31" is accepted and treated as "2015-10-01". But you should check first why payload.objectForKey("messageExpiry") returns an invalid date.

Answer 2

var str = "2015-09-29"

let dateFormatter = NSDateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd"
dateFormatter.locale = NSLocale(localeIdentifier: "en_US_POSIX")
let dateAsNSDate = dateFormatter.dateFromString(str)
print(dateAsNSDate)
// -> "Optional(2015-09-29 07:00:00 +0000)\n"

So that would appear to work. Looks like you just got too many days in your month, so it wasn't a valid date! :)