如何获取一个月中特定工作日的所有日子？答案

【问题标题】：How to get all days in a month that are a specific weekday?如何获取一个月中特定工作日的所有日子？
【发布时间】：2017-06-17 02:22:29
【问题描述】：

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？示例代码将不胜感激，因为我为此苦苦挣扎了好几天。

【问题讨论】：

标签： ios objective-c calendar nscalendar

【解决方案1】：

DateComponents 有一个 weekday 属性，表示星期几。工作日（在基金会的公历中）编号为 1 代表星期日，2 代表星期一，……，7 代表星期六。

一个DateComponents也有一个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.”

所以让我们为 2017 年 6 月的某个星期六初始化一个 DateComponents。如果您不关心时间，通常最好指定中午的时间，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)

让我们制作一个日历。

var calendar = Calendar.autoupdatingCurrent

现在我们可以遍历所有可能的工作日序数。对于每一个，我们都会要求日历生成一个日期。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，但大多数有 4 个。所以当我们要求第 5 个星期六时，我们可能会得到下个月的日期。发生这种情况时，我们希望取消该日期。

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);
}

【讨论】：

【解决方案2】：

这是使用calendar 方法称为enumerateDates 并使用Date 扩展的另一种解决方案

    //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
    }

扩展

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())!
    }
}

使用它

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))
    }
}

输出

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

希望对你有帮助

【讨论】：