Swift 4 and Xcode 9: Cannot invoke 'dateComponents' with an argument list of type '(NSCalendar.Unit.Type, from: NSData, to: Date?)'

Question

Trying to create a countdown timer, but I can't get past this error:

Cannot invoke 'dateComponents' with an argument list of type '(NSCalendar.Unit.Type, from: NSData, to: Date?)'

my code:

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var TimerLable: UILabel!



    let formatter = DateFormatter()
    let userCleander = Calendar.current;
    let CalenderComponent : NSCalendar.Unit = [
        NSCalendar.Unit.year,
        NSCalendar.Unit.month,
        NSCalendar.Unit.day,
        NSCalendar.Unit.hour
    ]


    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

    }
    func printTime()
    {
        formatter.dateFormat = "dd/MM/yy hh:mm a"
        let StartTime = NSData()
        let EndTime = formatter.date(from: "10/08/19 12:00 a")

        let TimeDifference = userCleander.dateComponents(NSCalendar.Unit, from: StartTime, to: EndTime)
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }



}

Answer 1

The main issue which causes the error is just a typo. StartTime is supposed to be NSDate not NSData.

Basically don't use NS... classes if there is a Swift native counterpart (Calendar, Date etc).

The Swift 3+ code is

let formatter = DateFormatter()
let userCalendar = Calendar.current

let calendarComponents : Set<Calendar.Component> = [ .year, .month, .day, .hour]

func printTime()
{
    formatter.dateFormat = "dd/MM/yy hh:mm a"
    let startTime = Date()
    let endTime = formatter.date(from: "10/08/19 12:00 am")!

    let timeDifference = userCalendar.dateComponents(calendarComponents, from: startTime, to: endTime)
}

Two notes:

• According to the naming guidelines variable names start with a lowercase letter
• The date format does not match the date string and the created date needs to be unwrapped.