ios - Swift Problems understanding the result of Calendar.dateComponents -


in app have list of contacts including contacts birthday. want see of contacts have birthday within in next 7 days. using filter on list filter , return thos contacts match

     let timespan = 7      let cal = calendar.current      let = date()      var birthdays = contactlist.filter { (contact) -> bool in         if let birthdate = contact.birthdate {             let difference = cal.datecomponents([.day,.year], from: birthdate date, to: now! )             print("bd:\(birthdate) : diff \(difference.day!)")             return ((difference.day! <= timespan) && difference.day! >= 0)         }         return false     }

my hope so. result weired. added ugly print closure in order see result of 'difference'

what odd instance following: today 2017-08-18 1 of contacts born on 1987-08-19. instead of returning difference.day of 1 receive 364. if swap from: , to: in datecomponents receive difference.day of -364.

my expectation have difference.day = 1.

again in playground

import uikit var = date() let dateformatter = dateformatter()  dateformatter.dateformat = "yyyy-mm-dd" let s = dateformatter.date(from: "1987-08-19")  let cal = calendar.current  let difference = cal.datecomponents([calendar.component.day,calendar.component.month,calendar.component.year], from: s!, to: ) print("\(difference.day!)") // result difference.day = 30

what doing wrong?

thanks

you can create extension return number of days next birthday follow:

extension date {     var year:  int { return calendar.current.component(.year, from: self)  }     var month: int { return calendar.current.component(.month, from: self) }     var day:   int { return calendar.current.component(.day, from: self)   }     var noon: date { return calendar.current.date(bysettinghour: 12, minute: 0, second: 0, of: self)! }     var daysfrombirthday: int {         let nextbirthdate = datecomponents(calendar: .current, year: date().year + (month < date().month ? 1 : 0), month: month, day: day, hour: 12).date ?? date.distantfuture         return calendar.current.datecomponents([.day], from: date().noon, to: nextbirthdate).day ?? 0     } }

and can filter objects follow:

let timespan = 0...7  let birthdays = contactlist.filter {     timespan ~= $0.birthdate?.daysfrombirthday ?? -1 }

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