如何获得特定工作日的一个月的所有日子？

Question

How do I get the actual date of the month based on a given a day ? For example, I would like to retrieve all the dates in June 2017 which are Saturday. How can I achieve that ? Sample code will be very much appreciated as I have struggled for days on this.

Answer 1

A DateComponents has a weekday property, representing the day of the week. The weekdays are (in Foundation's Gregorian calendar) numbered 1 for Sunday, 2 for Monday, …, and 7 for Saturday.

A DateComponents also has a weekdayOrdinal property, representing “ the position of the weekday within the next larger calendar unit, such as the month. For example, 2 is the weekday ordinal unit for the second Friday of the month. ”

So let's initialize a DateComponents for some Saturday in June 2017. It's generally a good idea to specify a time of noon if you don't care about the time, because midnight (the default time of day) can cause problems in some time zones on some days .

var components = DateComponents(era: 1, year: 2017, month: 06, hour: 12, weekday: 7)

And let's make a calendar.

var calendar = Calendar.autoupdatingCurrent

Now we can loop over all the possible weekday ordinals. For each, we'll ask the calendar to generate a date. Then we ask the calendar to convert the date back to year, month, and day components.

In the Gregorian calendar, some months have 5 Saturdays, but most have 4. So when we ask for the 5th Saturday, we'll probably get a date in the following month. When that happens, we want to suppress that date.

for i in 1 ... 5 {
    components.weekdayOrdinal = i
    let date = calendar.date(from: components)!
    let ymd = calendar.dateComponents([.year, .month, .day], from: date)
    guard ymd.month == components.month else { break }
    print("\(ymd.year!)-\(ymd.month!)-\(ymd.day!)")
}

Output:

2017-6-3
2017-6-10
2017-6-17
2017-6-24

Objective-C version:

NSDateComponents *components = [NSDateComponents new];
components.era = 1;
components.year = 2017;
components.month = 6;
components.hour = 12;
components.weekday = 7;
NSCalendar *calendar = NSCalendar.autoupdatingCurrentCalendar;

for (NSInteger i = 1; i <= 5; ++i) {
    components.weekdayOrdinal = i;
    NSDate *date = [calendar dateFromComponents:components];
    NSDateComponents *ymd = [calendar components:NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay fromDate:date];
    if (ymd.month != components.month) { break; }
    NSLog(@"%ld-%ld-%ld", (long)ymd.year, (long)ymd.month, (long)ymd.day);
}

Answer 2

This is another solution for your problem using calendar method called enumerateDates and using a Date extension

    //month in MM format, year in yyyy format and dayNumber as Int 1 for sunday, 7 for saturday
    func datesWith(dayNumber:Int,month:String,year:String) -> [Date]
    {
        assert(dayNumber >= 1 && dayNumber <= 7, "Day number is wrong")

        let dateFormatter = DateFormatter()
        dateFormatter.dateFormat = "yyyy-MM-dd"
        let date = dateFormatter.date(from: year + "-" + month + "-" + "01")

        guard date != nil else {
            return []
        }
        var resultDates : [Date] = []

        //check if firstDay of month is desired weekday
        if(Calendar.current.component(.weekday, from: date!) == dayNumber)
        {
            resultDates.append(date!)
        }

        Calendar.current.enumerateDates(startingAfter: date!, matching: DateComponents(weekday: dayNumber), matchingPolicy: Calendar.MatchingPolicy.nextTimePreservingSmallerComponents) { (currentDate, result, stop) in
            if(currentDate! > date!.endOfMonth())
            {
                stop = true
                return
            }
            resultDates.append(currentDate!)
        }

        return resultDates
    }

Extension

extension Date {
    func startOfMonth() -> Date {
        return Calendar.current.date(from: Calendar.current.dateComponents([.year, .month], from: Calendar.current.startOfDay(for: self)))!
    }

    func endOfMonth() -> Date {
        return Calendar.current.date(byAdding: DateComponents(month: 1, day: -1), to: self.startOfMonth())!
    }
}

Using it

override func viewDidLoad() {
    super.viewDidLoad()

    let dateFormatter = DateFormatter()
    dateFormatter.dateFormat = "yyyy-MM-dd"
    // Do any additional setup after loading the view, typically from a nib.
   let datesArray = self.datesWith(dayNumber: 5, month: "06", year: "2017")
    for currDate in datesArray {
        debugPrint(dateFormatter.string(from: currDate))
    }
}

Output

"2017-06-01"
"2017-06-08"
"2017-06-15"
"2017-06-22"
"2017-06-29"

Hope this helps