如何获取给定周数和年份的第一个和最后一个日期？

Question

我是 ios 编程新手，我拼命想用参考年份获取一周的第一个和最后一个日期。

我尝试构建一个方法，但确实得到了奇怪的日期。

+ (NSArray*)getStartDateOfWeek : (NSInteger)weekNumber withYear:(NSInteger)year {
    NSMutableArray *result = [[NSMutableArray alloc]init];

    // Week Start Date

    NSCalendar *gregorianStart = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
    NSDateComponents *componentsStart = [[NSDateComponents alloc] init];


    [componentsStart setWeekOfYear:weekNumber];
    [componentsStart setYear:year];

    int startDayOfWeek = [[[NSCalendar currentCalendar] components:NSWeekdayCalendarUnit fromDate:[gregorianStart dateFromComponents:componentsStart]] weekday];
    [componentsStart setDay:([componentsStart day] - ((startDayOfWeek) - 2))];

    NSDate *beginningOfWeek = [gregorianStart dateFromComponents:componentsStart];

    // Week End Date

    NSCalendar *gregorianEnd = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];

    NSDateComponents *componentsEnd = [[NSDateComponents alloc]init];
    [componentsStart setWeekOfYear:weekNumber];
    [componentsStart setYear:year];

    int endDayOfWeek = [[[NSCalendar currentCalendar] components:NSWeekdayCalendarUnit fromDate:[gregorianEnd dateFromComponents:componentsEnd]] weekday];

    [componentsEnd setDay:([componentsEnd day]+ (7 - endDayOfWeek) + 1)]; // for end day of the week

    NSDate *endOfWeek = [gregorianEnd dateFromComponents:componentsEnd];

    [result insertObject:beginningOfWeek atIndex:0];
    [result insertObject:endOfWeek atIndex:1];

    return result;
}

感谢任何帮助。

Answer 1

假设您想要给定一周的星期日（第一天）和星期六（最后一天），此代码将执行您想要的操作（为清楚起见，我创建了两种方法，但您可以将它们组合回一个） -

+ (NSDate *)firstDayOfWeek:(NSInteger)weekNumber inYear:(NSInteger)year
{
    NSDateComponents *comps=[[NSDateComponents alloc]init];
    [comps setWeekday:1];                                   //Change this to 2 if you want Monday rather than Sunday
    [comps setWeekOfYear:weekNumber];

    [comps setYear:year];
    [comps setYearForWeekOfYear:year];

    NSCalendar *cal=[[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];

    NSDate *newDate=[cal dateFromComponents:comps];

    return newDate;

}

+ (NSDate *)lastDayOfWeek:(NSInteger)weekNumber inYear:(NSInteger)year
{
    NSDateComponents *comps=[[NSDateComponents alloc]init];
    [comps setWeekday:7];                                  //Change this to 6 if you want Friday rather than Saturday
    [comps setWeekOfYear:weekNumber];

    [comps setYear:year];
    [comps setYearForWeekOfYear:year];

    NSCalendar *cal=[[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];

    NSDate *newDate=[cal dateFromComponents:comps];

    return newDate;

}

一个重要的点是[comps setYearForWeekOfYear:year]; - 否则您可能会在第 1 周得到意想不到的结果 - 默认情况下，您将获得一年中的“最后”第 1 周，这也是下一年的第 1 周，因此您结束比你预期的晚一年。

如果您想将两者合二为一，我会使用NSDictionary 而不是NSArray -

 +(NSDictionary *)firstAndLastDayOfWeek:(NSInteger)weekNumber inYear:(NSInteger)year
    {
        NSDateComponents *comps=[[NSDateComponents alloc]init];
        [comps setWeekday:1];
        [comps setWeekOfYear:weekNumber];

        [comps setYear:year];
        [comps setYearForWeekOfYear:year];

        NSCalendar *cal=[[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];

        NSDate *firstDay=[cal dateFromComponents:comps];

        [comps setWeekday:7];

        NSDate *lastDay=[cal dateFromComponents:comps];

        return @{@"firstDay":firstDay,@"lastDay":lastDay};

    }