Question

如何根据给定的一天获得当月的实际日期？例如，我想检索2017年6月的所有日期，即星期六。我怎样才能做到这一点？示例代码将非常受欢迎，因为我已经在这方面苦苦挣扎了几天。

Answer 1

DateComponents具有weekday属性，表示星期几。工作日（在基金会公历中）周日为1，周一为2，周六为7。

DateComponents也有weekdayOrdinal属性，代表“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.”

因此，让我们在2017年6月的某个星期六初始化一个DateComponents。如果您不关心时间，指定一个中午的时间通常是个好主意，因为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)

让我们制作日历。

var calendar = Calendar.autoupdatingCurrent

现在我们可以循环所有可能的工作日序数。对于每个人，我们会要求日历生成日期。然后我们要求日历将日期转换回年，月和日组件。

在公历中，有些月份有5个星期六，但大多数都有4个。所以当我们要求第5个星期六时，我们可能会在下个月得到一个日期。当发生这种情况时，我们想要压制那个日期。

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!)")
}

输出：

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

Objective-C版本：

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

这是使用名为calendar的{{1}}方法并使用enumerateDates扩展程序

的另一种解决方案

Date

扩展

    //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
    }

使用它

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())!
    }
}

输出

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))
    }
}

希望这有帮助

如何获得特定工作日的一个月的所有日子？

2 个答案: