Error Creating Simple Countdown to Date App in Swift 4 - swift

Question

So, I am currently working on an app that will do a simple countdown to a specific date; however, I am getting this error: "Value of type '(NSCalendar.Unit, Date, Date [NSCalendar.Options]) -> ()' has no member 'day' "
Any way to fix this to finish the app?
class ViewController: UIViewController {
#IBOutlet weak var CountdownText: UILabel!
let formatter = DateFormatter()
let userCalendar = NSCalendar.current
let requestedComponent: NSCalendar.Unit = [
NSCalendar.Unit.month,
NSCalendar.Unit.day,
NSCalendar.Unit.hour,
NSCalendar.Unit.minute,
NSCalendar.Unit.second,
]
func printTime()
{
formatter.dateFormat = "MM/dd/yy hh:mm:ss a"
let startTime = NSDate()
let endTime = formatter.date(from: "12/03/18 2:00:00 p")
func timeDifference (requestedComponent: NSCalendar.Unit, from: Date, to: Date, options: [NSCalendar.Options]) {}
CountdownText.text = "\(timeDifference.day) Days \(timeDifference.minute) Minutes \(timeDifference.second) Seconds"
}
}

Answer 1

You're trying to get call .day property from your function type which does and returns nothing.
I bet your function timeDifference should be somewhere outside the printTime function.
Believe you want to do something like following:
func printTime() {
formatter.dateFormat = "MM/dd/yy hh:mm:ss a"
let startTime = Date()
let endTime = formatter.date(from: "12/03/18 2:00:00 p")
let days = timeDifference(requestedComponent: .day, from: startTime, to: endTime, options: [])
let minutes = timeDifference(requestedComponent: .minute, from: startTime, to: endTime, options: [])
let seconds = timeDifference(requestedComponent: .second, from: startTime, to: endTime, options: [])
CountdownText.text = "\(days) Days \(minutes) Minutes \(seconds) Seconds"
}
func timeDifference (requestedComponent: NSCalendar.Unit, from: Date, to: Date, options: [NSCalendar.Options]) -> Int {
var calculatedValue = 0
// calculatings
return calculatedValue
}

Answer 2

You've declared a function named timeDifference() and you're trying to access it like a variable instance
Here's what you need to do:-
func timeDifference (requestedComponent: NSCalendar.Unit, from: Date, to: Date, options: [NSCalendar.Options]) {
//Do your things here
}
And call the function inside the variable this way:-
var text = "\(timeDifference(requestedComponent: .day, from: Date(), to: Date(), options: [.searchBackwards])) Days \(timeDifference(requestedComponent: .minute, from: Date(), to: Date(), options: [.searchBackwards])) Minutes \(timeDifference(requestedComponent: .second, from: Date(), to: Date(), options: [.searchBackwards])) Seconds"
Additionally, you can make your function parameters optional like this:-
func timeDifference (requestedComponent: NSCalendar.Unit, from: Date, to: Date, options: [NSCalendar.Options]? = nil) {}
The fourth parameter here is optional and the you don't have to provide an option every time. It's considered to be nil without input and it won't affect you in any way, unless you use it somewhere within the function, where you might have to handle it with an 'if' statement
(Just in case if it helps!)
NOTE:-
You can also return a "NSCalendar.Unit" from your function and use it for calculation, in which case, your usage pattern is right.
But I assume that the function here is written for the purpose of calculation and you're dealing with a label's value to display the calculated result. Dealing this all within a function is the sole purpose of a function, and hence I recommend doing this

Answer 3

You are trying to use function (with no return type) as NSCalendarComponent, hence it is showing you error. Instead, you and get start time and end time components like this:
func printTime(){
formatter.dateFormat = "MM/dd/yy hh:mm:ss a"
let calendar = Calendar.current
let startTime=calendar.dateComponents([.hour,.minute,.second], from: Date())
print("\(startTime.hour!):\(startTime.minute!):\(startTime.second!)")
let endTime = calendar.dateComponents([.hour,.minute,.second], from: formatter.date(from: "12/03/18 2:00:00 p") ?? Date())
print("\(endTime.hour!):\(endTime.minute!):\(endTime.second!)")
//do calculations here for time difference
}
and now you can calculate time difference and show it on countdown text.

Answer 4

First of all don't use NSCalendar and NSDate at all in Swift 3+.
Your code doesn't work because the function timeDifference has no return value and does nothing anyway.
You probably mean
let requestedComponents: Set<Calendar.Component> = [.month, .day, .hour, .minute, .second]
...
func timeDifference (requestedComponents: Set<Calendar.Component>, from: Date, to: Date) -> DateComponents {
return Calendar.current.dateComponents(requestedComponents, from: from, to: to)
}
...
let difference = timeDifference(requestedComponents: requestedComponents, from: startTime, to: endTime)
CountdownText.text = "\(difference.day!) Days \(difference.minute!) Minutes \(difference.second!) Seconds"
There is a more convenient way to calculate and display time differences, DateComponentsFormatter
func printTime()
{
let formatter = DateFormatter()
formatter.dateFormat = "MM/dd/yy hh:mm:ss a"
let startTime = Date()
let endTime = formatter.date(from: "12/03/18 2:00:00 p")!
let componentsFormatter = DateComponentsFormatter()
componentsFormatter.allowedUnits = [.hour, .minute, .second]
componentsFormatter.unitsStyle = .full
CountdownText.text = componentsFormatter.string(from: startTime, to: endTime)
}