Get a Week From a Different Starting Day

Question

Before I try this with my approach (which I have a feeling is simplistic and too drawn out), I wanted to ask anyone if there is an easier / more direct way in Swift.

The task is to let the user pick any day in the calendar. So let's say they pick Tuesday a month ago. Now I want to put that entire week into an array. So the Monday before, then Tues, then Wednesday, Thurs, Fri, Sat, Sun. So the array would always hold 7 days.

Here is the thing - I'd like to change this up so the user can define what their "start day" is - for example if I assign Thursday as my starting day, then if I were to pick a random Tuesday again from a few months back, the array should look like this: [Thurs/Fri/Sat/Sun/Mon/Tues/Wed] (the array always starts with the user's starting day) and will go backwards a week if you pick a date before your start date. So for example if I selected Tuesday the 14, then it would go back to the Thursday the 9th as the starting day.

My approach was to simply do a loop, starting from the day the user specifies, and walking backwards until I've reached my start date, and then walk forwards until I hit the corresponding end date.

Is there a better approach instead of doing something like that? Maybe some nifty NSDateComponents i'm not ware of or some such?

Thanks for your help as always!

What if you pick the day after your starting day - so if the starting day is Thursday and you pick a friday - do you want the week from the Thursday the day before the selected day or from the next Thursday i.e. after the selected day? — Paulw11

Martin R Martin R · Accepted Answer · 2014-08-06T05:25:35

You can set the firstWeekday property of the current calendar to determine the first day of the week for all calendrical calculations:

let cal = NSCalendar.currentCalendar()
cal.firstWeekday = 5 // 1 == Sunday, 5 == Thursday

Use rangeOfUnit to determine the start and of the week containing the chosen date:

let chosenDate = ...
var startOfWeek : NSDate? = nil
var lengthOfWeek : NSTimeInterval = 0
cal.rangeOfUnit(.WeekCalendarUnit, startDate: &startOfWeek, interval:&lengthOfWeek, forDate: chosenDate)
var endOfWeek = startOfWeek!.dateByAddingTimeInterval(lengthOfWeek)

Iterate over the dates:

var date = startOfWeek!
let formatter = NSDateFormatter()
formatter.dateFormat = "EEEE, dd.MM.yyyy"

while date.compare(endOfWeek) == NSComparisonResult.OrderedAscending  {
    println(formatter.stringFromDate(date))
    date = cal.dateByAddingUnit(.DayCalendarUnit, value: 1, toDate: date, options: NSCalendarOptions(0))
}

Example output (for today as the chosen date):

Thursday, 31.07.2014
Friday, 01.08.2014
Saturday, 02.08.2014
Sunday, 03.08.2014
Monday, 04.08.2014
Tuesday, 05.08.2014
Wednesday, 06.08.2014

Get a Week From a Different Starting Day

1 Answers