Dateformatter Doesn't Return Date For "Hh:Mm:Ss"

DateFormatter doesn't return date for HH:mm:ss

From Technical Q&A QA1480 – NSDateFormatter and Internet Dates (emphasis added):

On the other hand, if you're working with fixed-format dates, you should first set the locale of the date formatter to something appropriate for your fixed format. In most cases the best locale to choose is "en_US_POSIX", a locale that's specifically designed to yield US English results regardless of both user and system preferences.

This will prevent the date from being interpreted according to
the user's regional settings:

let dateFormatter = DateFormatter()
// Set the locale first ...
dateFormatter.locale = Locale(identifier: "en_US_POSIX")
// ... and then the date format:
dateFormatter.dateFormat = "HH:mm:ss"

// ...

See also What is the best way to deal with the NSDateFormatter locale "feechur"?.

Date format ( yyyy-MM-dd HH:mm:ss VV) returns nil

You should always set the locale of your DateFormatter when dealing with hardcoded Date formats. You can use en_US_POSIX in most scenarios.

let dateString = "2016-01-21 00:29:09 Etc/GMT"
let dateFormatter = DateFormatter()
dateFormatter.locale = Locale(identifier: "en_US_POSIX")
dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss VV"
let dateObject = dateFormatter.date(from: dateString)
print(dateObject)

Swift `yyyy-MM-dd'T'HH:mm:ss.sssZ` string to date

Your format is wrong. It should be:

"yyyy-MM-dd'T'HH:mm:ss.SSSZ"

Have a look at date time format here:
https://unicode.org/reports/tr35/tr35-dates.html#Date_Format_Patterns

Issue in formatting Date in swift 4

HH:mm:ss gives you the time in 24 hour format, so a doesn't make sense inside the format. Or you can use hh:mm:ss a.

Date() gives you the time in UTC. You need to provide the timezone information to get the date in your timezone.

    let date = Date()
    let dateFormatter = DateFormatter()
    dateFormatter.dateFormat = "dd-MMM-yyyy HH:mm:ss"
    dateFormatter.timeZone = .current
    let localDate = dateFormatter.string(from: date)
    
    print(localDate)

localDate will give you the date in your current timezone.

DateFormatter date from string returns nil when iPhone Date & Time 24-Hour Time is off

You're using a very standardized timestamp format, which allows you to take advantage of the ISO8601DateFormatter.

let dateString = "2020-03-05T09:00:00+00:00"

let df = ISO8601DateFormatter()
df.formatOptions = [.withInternetDateTime]

if let date = df.date(from: dateString) {
    print(date) // 2020-03-05 09:00:00 +0000
}

If a machine (like your server) is generating the timestamp then it will (should) always be in zulu time (GMT) so you don't need to do anything beyond this. You could specify a time zone but there isn't a point since the string will always zero it out for you.

df.timeZone = TimeZone(secondsFromGMT: 0)

This string represents an absolute moment in time. If you need a relative moment in time, such as the local time from the source, you'll need to identify that time zone and apply it here, which is also very straighforward.

Swift date from string conversion doesn't work but the format works with online service?

Small tip when you are working with DateFormatter, if it doesn't work one way, then do it the other way:

let string = dateFormatter.string(from: Date())
print("string: \(string)")

This way you'll see how your format is really interpreted.

If you do so, you'll get:

$> string: Fri, Aug 03, 2018, 12:05:09 GMT

See the extras , and the Aug 03 vs 03 Aug?

Now, your issue is that you misunderstood localizedDateFormatFromTemplate.

In fact you could remove spaces, punctuations and order.
For instance, dateFormatter.setLocalizedDateFormatFromTemplate("ddyyyyHHmmsszEMMM") gives the same output.

You just needs to give it what kind of infos you want (day, year, months, etc.), and it create the correct dateFormat corresponding in the localized version (adding then extra punctuations, etc.).

So use instead:

dateFormatter.dateFormat = "EEE, dd MMM yyyy HH:mm:ss z"

Side note:
I currently live in GMT+2, so I added dateFormatter.timeZone = TimeZone(secondsFromGMT: 0) to make it work.

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