获取一个月的所有 NSDate（以及相邻周的日期）

Question

Given a date (for example today 4 Feb 2014 ), I would like to get a list of NSDate instances that go from Monday 27 Jan 2014 to Sunday 2 Mar 2014 .

Basically all the dates in the current month, plus the dates from the last week of the previous month, and the first week of the next month, if they share the same week with some of the dates in the current month.

How can I achieve this?

I can think of a way to obtain this (pseudo-code below), but it's way too long and complicated. Is there any simpler way, like a method that the SDK provides to short cut?

1. Extract the month component from [NSDate date] (today)
2. Construct the first day of the month
3. Calculate its weekday
4. If it's Wednesday (3rd day of the week) then add today-1, today-2 to the list and so on
5. Repeat from step 2, but with the last day of the month

Also to all the elitists out there, just because I'm not posting any code, doesn't mean this is not a coding question. The problem is real (construct a calendar grid of a month), and finding the right algorithm/method before coding is much better than playing around and manually do the maths with NSDate and NSCalendar (very error prone, as I will need to take into account all the weird cases). I figure many people have already encountered this same problem and if they could share some pointers, great. If you don't want to answer, no need to reply.

Answer 1

I'm going to post very general code. You are going to need to make it specific to your needs.

//Setup the calendar object
NSCalendar *calendar = [NSCalendar currentCalendar];

//Get the current date's month
NSUInteger month = [dateComponents month];

//Create an NSDate for the first and last day of the month
NSDateComponents *comp = [calendar components:(NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit) fromDate:[NSDate date]];
[comp setDay:1];
NSDate *firstOfMonth = [calendar dateFromComponents:comp];
[comp setMonth:[comp month]+1];
[comp setDay:0];
NSDate *lastOfMonth = [calendar dateFromComponents:comp];

//Now get the first and last week number from there
NSUInteger unitFlags = NSWeekCalendarUnit;
//Create a date component object from today's date.
NSDateComponents *firstDateComponents = [calendar components:unitFlags
                                                   fromDate:firstOfMonth // for current date
                                                    options:0];
NSDateComponents *lastDateComponents = [calendar components:unitFlags
                                                   fromDate:lastOfMonth // for current date
                                                    options:0];


NSUInteger firstWeek = [firstDateComponents week];
NSUInteger lastWeek = [lastDateComponents week];

Now that you have the first and last weeks you can start at the first day of the first week and go through the last day of the last week to set up your calendar. Good luck.

Answer 2

Swift 5:

extension Date {
    
    var startOfMonth: Date {
        
        let calendar = Calendar(identifier: .gregorian)
        let components = calendar.dateComponents([.year, .month], from: self)
        
        return  calendar.date(from: components)!
    }

    var endOfMonth: Date {
        var components = DateComponents()
        components.month = 1
        components.second = -1
        return Calendar(identifier: .gregorian).date(byAdding: components, to: startOfMonth)!
    }
}

let date = Date()

let firstWeek = Calendar.current.dateComponents([.weekOfYear], from: date.startOfMonth)
let lastWeek = Calendar.current.dateComponents([.weekOfYear], from: date.endOfMonth)