Swift 3 - find number of calendar days between two dates

Question

The way I did this in Swift 2.3 was:

let currentDate         = NSDate() let currentCalendar     = NSCalendar.currentCalendar()  var startDate : NSDate? var endDate   : NSDate?  // The following two lines set the `startDate` and `endDate` to the start of the day  currentCalendar.rangeOfUnit(.Day, startDate: &startDate, interval: nil, forDate: currentDate) currentCalendar.rangeOfUnit(.Day, startDate: &endDate, interval: nil, forDate: self)  let intervalComps = currentCalendar.components([.Day], fromDate: startDate!, toDate: endDate!, options: [])  print(intervalComps.day) 

Now this has all changed with Swift 3. I have to either use NSCalendar and NSDate by constantly type casting with as, or find the Swift 3 way of doing it.

What's the right way to do it in Swift 3?

Answer 1

In Swift 5 there is a simple one-liner to get the number of days (or any other DateComponent) between two dates:

let diffInDays = Calendar.current.dateComponents([.day], from: dateA, to: dateB).day 

Note: As pointed out in the comments, this solution measures the 24h periods and therefore requires at least 24h between dateA and dateB.

Answer 2

Turns out this is much simpler to do in Swift 3:

extension Date {          func interval(ofComponent comp: Calendar.Component, fromDate date: Date) -> Int {          let currentCalendar = Calendar.current          guard let start = currentCalendar.ordinality(of: comp, in: .era, for: date) else { return 0 }         guard let end = currentCalendar.ordinality(of: comp, in: .era, for: self) else { return 0 }          return end - start     } } 

Edit

Comparing the ordinality of the two dates should be within the same era instead of the same year, since naturally the two dates may fall in different years.

Usage

let yesterday = Date(timeInterval: -86400, since: Date()) let tomorrow = Date(timeInterval: 86400, since: Date())   let diff = tomorrow.interval(ofComponent: .day, fromDate: yesterday) // return 2