How to change string to date without converting to any timezone in Swift?

I know there are lot of questions passing around over this simple issue, but still I couldn't get a clear idea.

Here is what I want:

SelectedDateString = "19-08-2015 09:00 AM"
let dateFormatter = NSDateFormatter()
dateFormatter.dateFormat = "dd-MM-yyyy HH:mm a"
dateFormatter.timeZone = NSTimeZone();
let SelectedUTCDate = dateFormatter.dateFromString(SelectedDateString)!
println("SelectedLocalDate = \(SelectedLocalDate)") 
// OUTPUT: SelectedLocalDate = 2015-08-18 18:30:00 +0000

If I dont use TimeZone:

let dateFormatter = NSDateFormatter()
dateFormatter.dateFormat = "dd-MM-yyyy HH:mm a"
// dateFormatter.timeZone = NSTimeZone();
let SelectedUTCDate = dateFormatter.dateFromString(SelectedDateString)!
println("SelectedLocalDate = \(SelectedLocalDate)")
//OUTPUT: SelectedLocalDate = 2015-08-18 19:26:00 +0000

Why is there change in the time and Date? What I want is:

//OUTPUT: SelectedLocalDate = 2015-08-19 09:00:00 +0000

Also I want to convert the Local Date to Exact UTC Date

//Like this: SelectedUTCDate = 2015-08-19 03:30:00 

inputString = "19-08-2015 10:45 am"  // My localtime is 10:35 AM, so I set 10 mins from now
 var currentUTCTime = NSDate() // currentUTCTime is 05: 15 AM.

I want to convert the inputString to its respective UTC Time and find the difference between the two times in both date and string.

//Like this Date: diffInDate: 00-00-0000 00:10 and
// Like this String: diffInString: 10 mins

How can I get both of these?

Solution

let dateString = "19-08-2015 09:00 AM"
let dateFormatter = DateFormatter()
dateFormatter.calendar = Calendar(identifier: .iso8601)
dateFormatter.locale = Locale(identifier: "en_US_POSIX")
dateFormatter.timeZone = TimeZone(secondsFromGMT: 0)
dateFormatter.dateFormat = "dd-MM-yyyy hh:mm a"
if let dateFromString = dateFormatter.date(from: dateString) {
    print(dateFromString)   // "2015-08-19 09:00:00 +0000"
    dateFormatter.timeZone = .current
    dateFormatter.dateFormat = "dd-MM-yyyy hh:mm a Z"
    dateFormatter.string(from: dateFromString)  // 19-08-2015 06:00 AM -0300"
}