如何在本月下周的第一天获得NSDate

Question

给定一个任意日期,我需要找到该月下一周第一天的日期.请注意,它并不像在当前日期添加7天那么简单,因为该月的最后一周可能少于7天.这是我现在使用的代码:

    NSCalendar* calendar = [NSCalendar currentCalendar];
    NSDateComponents* components = [calendar components:NSWeekOfMonthCalendarUnit|NSYearCalendarUnit|NSMonthCalendarUnit|NSWeekCalendarUnit|NSDayCalendarUnit fromDate:currentDate];

    NSLog(@"week of month: %ld", [components weekOfMonth]);

    [components setWeekOfMonth:[components weekOfMonth] + 1];
    NSLog(@"new week of month: %ld", [components weekOfMonth]); //week of month is now 2

    [components setWeekday:1];
    NSDate *nextWeek = [calendar dateFromComponents:components];

例如,currentDate设置为2012-10-01.在这个例子中,nextWeek始终是2012-10-01.似乎发送setWeekOfMonth:不会增加NSDateComponents对象中的其他日期组件.我是否配置了错误的日期组件,或者setWeekOfMonth:不应该这样工作？

Answer 1

所以....让我们从一个NSDate和一个开始NSCalendar:

NSDate *date = ...;
NSCalendar *cal = [NSCalendar currentCalendar];

弄清楚该日期的哪一天是:

NSInteger weekdayOfDate = [cal ordinalityOfUnit:NSWeekdayCalendarUnit inUnit:NSWeekCalendarUnit forDate:date];
NSInteger numberOfDaysToStartOfCurrentWeek = weekdayOfDate - 1;

让我们将该日期移至下周:

NSDateComponents *oneWeek = [[NSDateComponents alloc] init];
[oneWeek setWeek:1]; // add one week
[oneWeek setDay:-numberOfDaysToStartOfCurrentWeek]; // ... and subtract a couple of days to get the first day of the week
NSDate *startOfNextWeek = [cal dateByAddingComponents:oneWeek toDate:date options:0];

此时,您的日期指向下周的第一天.现在我们应该验证它仍然在同一个月:

NSDateComponents *monthOfNextWeek = [cal components:NSMonthCalendarUnit fromDate:startOfNextWeek];
NSDateComponents *monthOfThisWeek = [cal components:NSMonthCalendarUnit fromDate:date];
if ([monthOfNextWeek month] != [monthOfThisWeek month]) {
  // the first day of the next week is not in the same month as the start date
}

当我运行这个时,我知道下周的开始时间是2012年12月30日(星期日,因为我的日历星期日开始于星期日).

但是,如果我希望星期一的第一天开始,我可以在这个代码前面加上:

[cal setFirstWeekday:2]; // the first day of the week is the second day (ie, Monday, because Sunday = 1)

如果我这样做,那么startOfNextWeek结果将在2012年12月31日.