Compare ISO8601 format dates in Swift | iOS

Question

Im trying to compare two dates along with time (which are in format ISO8601). I've implemented below logic but the object returns nil(this will not take care of time which I need). Please advice what needs to done

eg: when two dates "2017-01-25T01:00:00.00" and "2018-01-25T01:00:00.00"is compared, it should return true (i.e., secondDate > firstDate) taking time into consideration

    //Date Formatter
    let dateFormatter = DateFormatter()
    let dateFormatString = "2017-01-25T01:00:00.00"
    dateFormatter.dateFormat = dateFormatString
    dateFormatter.calendar = Calendar(identifier: Calendar.Identifier.iso8601)
    dateFormatter.locale = Locale(identifier: "en_EN_POSIX")
    dateFormatter.timeZone = TimeZone(secondsFromGMT: 0)

    //Get Dates from ISO8601 format 
    var dateString: Date?
    var dateFromAPI: Date?
    //Date from string value (defaultFirstDate is string value)
    if let firstDate = defaultFirstDate, let truncatedDate = firstDate.components(separatedBy: "T").first{ 
    //Issue is with below line - it returns nil
        dateString = dateFormatter.date(from: truncatedDate)
    }
    if let secondDate = defaultSecondDate, let truncatedDate = secondDate.components(separatedBy: "T").first { 
    //Issue is with below line - it returns nil
        dateFromAPI = dateFormatter.date(from: truncatedDate)
    }


    if let date1 = dateString, let date2 = dateFromAPI, date1.compare(date2) == ComparisonResult.orderedAscending {
        showPage = true
    }