Question

我希望显示NSDate对象的月数。

//Make Date Six Months In The Future
NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSDateComponents *sixMonthsFromNow = [[NSDateComponents alloc] init];
[sixMonthsFromNow setMonth:6];
NSDate *finishDate = [calendar dateByAddingComponents:sixMonthsFromNow toDate:[NSDate date] options:0]; //Six Months Time

//Display
NSCalendarUnit requiredFormat = NSMonthCalendarUnit | NSDayCalendarUnit | NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit;
NSDateComponents *dateComponents  = [calendar components:requiredFormat fromDate:[NSDate date] toDate:finishDate options:0];

NSLog(@"%d months %d days %d hours %d minutes %d seconds", [dateComponents month], [dateComponents day], [dateComponents hour], [dateComponents minute], [dateComponents second]);

输出：5 months 29 days 23 hours 59 minutes 59 seconds

哪个好，但我只希望显示月数。

如果我只限制几个月：

//Make Date Six Months In The Future
NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSDateComponents *sixMonthsFromNow = [[NSDateComponents alloc] init];
[sixMonthsFromNow setMonth:6];
NSDate *finishDate = [calendar dateByAddingComponents:sixMonthsFromNow toDate:[NSDate date] options:0]; //Six Months Time

//Display
NSCalendarUnit requiredFormat = NSMonthCalendarUnit;
NSDateComponents *dateComponents  = [calendar components:requiredFormat fromDate:[NSDate date] toDate:finishDate options:0];
NSLog(@"%d months", [dateComponents month]);

输出：5 months

虽然这在技术上是正确的，但我希望将天数调整为六个月。

有没有简单的方法来达到这个效果？我注意到NSDateComponents上没有舍入属性。我是否必须手动检查天数并决定整理？

我的最终目标是不仅将舍入效果限制为几个月，如果我只提供，则应该可以将小时数限制为几天：NSDayCalendarUnit

Answer 1

以下方法可以满足您的需求。这个想法是在计算（向下舍入）数量的日历单位之后在开始日期和结束日期之间，将该金额和一个金额添加到开始日期并检查哪一个更接近结束日期：

@interface NSCalendar (MyCategory)
-(NSInteger)roundedUnit:(NSCalendarUnit)unit fromDate:(NSDate *)fromDate toDate:(NSDate *)toDate;
@end

@implementation NSCalendar (MyCategory)
-(NSInteger)roundedUnit:(NSCalendarUnit)unit fromDate:(NSDate *)fromDate toDate:(NSDate *)toDate
{
    // Number of units between the two dates:
    NSDateComponents *comps = [self components:unit fromDate:fromDate toDate:toDate options:0];
    NSInteger value = [comps valueForComponent:unit];

    // Add (value) units to fromDate:
    NSDate *date1 = [self dateByAddingComponents:comps toDate:fromDate options:0];

    // Add (value + 1) units to fromDate:
    [comps setValue:(value + 1) forComponent:unit];
    NSDate *date2 = [self dateByAddingComponents:comps toDate:fromDate options:0];

    // Now date1 <= toDate < date2. Check which one is closer,
    // and return the corresponding value:
    NSTimeInterval diff1 = [toDate timeIntervalSinceDate:date1];
    NSTimeInterval diff2 = [date2 timeIntervalSinceDate:toDate];
    return (diff1 <= diff2 ? value : value + 1);
}
@end

你会用它作为

NSInteger months = [calendar roundedUnit:NSMonthCalendarUnit fromDate:[NSDate date] toDate:finishDate];

代码使用NSDateComponents的实用程序方法 https://github.com/henrinormak/NSDateComponents-HNExtensions/blob/master/README.md：

- (void)setValue:(NSInteger)value forComponent:(NSCalendarUnit)unit;
- (NSInteger)valueForComponent:(NSCalendarUnit)unit;

这些方法是OS X 10.9中的新增功能，但在iOS 7中不可用。

Answer 2

正如另一位评论者指出的那样，你两次打电话给NSDate，第二次约会比第一次稍晚。使用相同的日期对象两次，您将不会出现舍入错误。

关于如何舍入：

我认为NSCalendars日历计算方法没有内置任何舍入。

您需要确定这对您意味着什么。你可能会在中途回合。在这种情况下，您可以使用rangeOfUnit：inUnit：forDate方法向日历询问当前月份的天数，然后将该天数的一半添加到结束日期，然后询问月份。如果您只想“在一周内完成整理，那么只需要在结束日期之前添加一周，然后再询问差异数。”

Answer 3

我遇到了类似的问题：

let fmt1 = NSDateComponentsFormatter()

fmt1.allowedUnits = .CalendarUnitYear |
    .CalendarUnitMonth |
    .CalendarUnitDay

let dc1 = NSDateComponents()
dc1.month = 1
dc1.day = 15

// This occasionally outputs "1 month, 14 days" instead of
// "1 month, 15 days" when the formatter is constrained to
// years, months and days. If formatter is allowed to use
// all units, the output is "1 month, 14 days, 23 hours,
// 59 minutes, 59 seconds".
fmt1.stringFromDateComponents(dc1)

这可以通过指定正秒数并将其组合来解决将maximumUnitCount格式化程序参数设置为固定值：

let fmt2 = NSDateComponentsFormatter()

fmt2.allowedUnits = .CalendarUnitYear |
    .CalendarUnitMonth |
    .CalendarUnitDay

fmt2.maximumUnitCount = 2
fmt2.collapsesLargestUnit = true

let dc2 = NSDateComponents()
dc2.month = 1
dc2.day = 15
dc2.second = 10

// This always outputs "1 month, 15 days"
fmt2.stringFromDateComponents(dc2)

此修复程序也可能适用于您的情况：只需在调用NSDateComponents之前为dateByAddingComponents分配一些正数秒：

[sixMonthsFromNow setMonth: 6];
[sixMonthsFromNow setSecond: 10];

NSDateComponent舍入

3 个答案: