NSDateComponents returns wrong weekday - ios

Question

If you'll run this code:
// January 16th 2015 10:20 AM in Amsterdam
var date = NSDate(timeIntervalSince1970: 1421400000)
var formatter = NSDateFormatter()
formatter.dateFormat = "dd-MMM"
let calendar = NSCalendar.currentCalendar()
calendar.firstWeekday = 2 // default when region == Netherlands
let units = NSCalendarUnit.YearCalendarUnit | NSCalendarUnit.MonthCalendarUnit
| NSCalendarUnit.WeekOfMonthCalendarUnit | NSCalendarUnit.DayCalendarUnit
| NSCalendarUnit.WeekdayCalendarUnit
// Loop days in January
for day in 1...14 {
// select day in month
var components = calendar.components(units, fromDate: date)
components.day = day
// get day and components
let _date = calendar.dateFromComponents(components)!
var _components = calendar.components(units, fromDate: _date)
// retrieve characteristics
let weekOfMonth = _components.weekOfMonth
let dayOfWeek = _components.weekday
let month = _components.month
println("\(formatter.stringFromDate(_date)) is day \(dayOfWeek) of week \(weekOfMonth) of month \(month) \n")
}
You'll probably get back:
01-Jan is day 5 of week 1 of month 1
02-Jan is day 6 of week 1 of month 1
03-Jan is day 7 of week 1 of month 1
04-Jan is day 1 of week 1 of month 1
05-Jan is day 2 of week 2 of month 1
06-Jan is day 3 of week 2 of month 1
07-Jan is day 4 of week 2 of month 1
....
Those weekdays are wrong.
Not only should the the 1st of january be the 4th day (a thursday), it's also strange that the 3rd of january seems to be on day 7 of week 1 and the 4th of january seems to be day 1 of that same week.
Obviously I'm doing something wrong here, who could help me out?
When you remove the calendar.firstWeekday = 2 line you'll get:
01-Jan is day 5 of week 1 of month 1
02-Jan is day 6 of week 1 of month 1
03-Jan is day 7 of week 1 of month 1
04-Jan is day 1 of week 2 of month 1
05-Jan is day 2 of week 2 of month 1
06-Jan is day 3 of week 2 of month 1
07-Jan is day 4 of week 2 of month 1
....
That makes more sense, but I really need the first day of the week to be a monday here..
I've set up a demo project for you to test this behaviour yourself. https://github.com/tiemevanveen/NSDateComponentsTest/tree/master
As sha points out, components.weekday does not change if your week does not start on a sSnday. Strange that components.weekOfMonth does change when your week starts on Monday..
Solution to my problem
An answer to another question let me to a way to find the desired weekday if the calendar's week does not start with a Sunday.
dayOfWeek = calendar.ordinalityOfUnit(.WeekdayCalendarUnit, inUnit: .WeekCalendarUnit, forDate: _date)
That code could also be used to find the week of the month or the month itself:
dayOfWeek = calendar.ordinalityOfUnit(.WeekdayCalendarUnit, inUnit: .WeekCalendarUnit, forDate: _date)
month = calendar.ordinalityOfUnit(.MonthCalendarUnit, inUnit: .YearCalendarUnit, forDate: _date)

Answer 1

It's all correct. If you look at Apple Documentation.
you can see that 1 is Sunday, 2 - is Monday and so forth. So 5 is Thursday as expected.