objective-c - objective-c 中当月的星期二数

Question

我正在寻找一种方法来计算 Objective-C 中当月星期二的数量。

例如，如果代码在今天(2012 年 7 月 16 日)运行，它将输出 5，因为 2012 年 7 月有 5 个星期二(第 3、10、17、24 和 31)。

我在网上看到了在 Excel 中执行此操作的解决方案，但我正在努力将其转换为 Objective C。

感谢您的帮助!好久了，第一次。

Answer 1

我们需要一个日历:

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

现在让我们获取当前的月份和年份:

    NSDate *now = [NSDate date];
    NSDateComponents *monthAndYear = [calendar components:NSMonthCalendarUnit | NSYearCalendarUnit fromDate:now];

我们可以用它来获取当前月份和年份的第一个星期二:

    NSDateComponents *firstTuesdayComponents = [monthAndYear copy];
    firstTuesdayComponents.weekday = 3; // Sunday = 1
    firstTuesdayComponents.weekdayOrdinal = 1; // First Tuesday
    NSDate *firstTuesday = [calendar dateFromComponents:firstTuesdayComponents];

我们也可以用它来获取下个月的第一天:

    NSDateComponents *firstOfNextMonthComponents = [monthAndYear copy];
    firstOfNextMonthComponents.month += 1;
    firstOfNextMonthComponents.day = 1;
    NSDate *firstOfNextMonth = [calendar dateFromComponents:firstOfNextMonthComponents];

现在我们可以查询两个日期之间的天数:

    NSDateComponents *differenceComponents = [calendar components:NSDayCalendarUnit fromDate:firstTuesday toDate:firstOfNextMonth options:0];

大多数周有 7 天，只有一个星期二，所以我们应该将天数除以 7。如果有余数，我们应该四舍五入，因为我们是从星期二开始计算的。

    int tuesdayCount = (differenceComponents.day + 6) / 7; // Adding 6 makes the integer division round up.
    NSLog(@"There are %d Tuesdays in month %d of year %d.", tuesdayCount, (int)monthAndYear.month, (int)monthAndYear.year);

现在让我们跳上时光机来测试一下:

There are 5 Tuesdays in month 1 of year 2012.
There are 4 Tuesdays in month 2 of year 2012.
There are 4 Tuesdays in month 3 of year 2012.
There are 4 Tuesdays in month 4 of year 2012.
There are 5 Tuesdays in month 5 of year 2012.
There are 4 Tuesdays in month 6 of year 2012.
There are 5 Tuesdays in month 7 of year 2012.
There are 4 Tuesdays in month 8 of year 2012.
There are 4 Tuesdays in month 9 of year 2012.
There are 5 Tuesdays in month 10 of year 2012.
There are 4 Tuesdays in month 11 of year 2012.
There are 4 Tuesdays in month 12 of year 2012.