iPhone - 获取两个日期之间的天数 [英] iPhone - get number of days between two dates

问题描述

我正在为iPhone撰写GTD应用程式。对于应有的任务，我要显示到期日或到期日或截止到7月18日。显然，即使任务不到24小时，我需要显示明天（例如，用户在星期六晚上11点检查，看到星期天上午8点有任务）。所以，我写了一个方法来获取两个日期之间的天数。这里是代码...

I'm writing a GTD app for the iPhone. For the due tasks, I want to display something like "Due tomorrow" or "Due yesterday" or "Due July 18th". Obviously, I need to display "Tomorrow" even if the task is less than 24 hours away (e.g. the user checks at 11pm on Saturday and sees there's a task on Sunday at 8am). So, I wrote a method to get the number of days in between two dates. Here's the code...

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"yyyy-MM-dd-HH-mm"];

NSDate *nowDate = [dateFormatter dateFromString:@"2010-01-01-15-00"];
NSDate *dueDate = [dateFormatter dateFromString:@"2010-01-02-14-00"];

NSLog(@"NSDate *nowDate = %@", nowDate);
NSLog(@"NSDate *dueDate = %@", dueDate);

NSCalendar *calendar = [NSCalendar currentCalendar];

NSDateComponents *differenceComponents = [calendar components:(NSDayCalendarUnit)
                                                     fromDate:nowDate
                                                       toDate:dueDate
                                                      options:0];

NSLog(@"Days between dates: %d", [differenceComponents day]);

...这里是输出：

NSDate *nowDate = 2010-01-01 15:00:00 -0700
NSDate *dueDate = 2010-01-02 14:00:00 -0700
Days between dates: 0

如您所见，此方法返回的结果不正确。它应该返回1作为两天之间的天数。我在这里做错了什么？

As you can see, the method returns incorrect results. It should have returned 1 as the number of days between the two days. What am I doing wrong here?

编辑：我写了另一种方法。我没有做过广泛的单元测试，但到目前为止似乎工作：

I wrote another method. I haven't done extensive unit tests, but so far it seems to work:

+ (NSInteger)daysFromDate:(NSDate *)fromDate inTimeZone:(NSTimeZone *)fromTimeZone untilDate:(NSDate *)toDate inTimeZone:(NSTimeZone *)toTimeZone {

    NSCalendar *calendar = [NSCalendar currentCalendar];
    unsigned unitFlags = NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit | NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit;

    [calendar setTimeZone:fromTimeZone];
    NSDateComponents *fromDateComponents = [calendar components:unitFlags fromDate:fromDate];

    [calendar setTimeZone:toTimeZone];
    NSDateComponents *toDateComponents = [calendar components:unitFlags fromDate:toDate];

    [calendar setTimeZone:[NSTimeZone defaultTimeZone]];
    NSDate *adjustedFromDate = [calendar dateFromComponents:fromDateComponents];
    NSDate *adjustedToDate = [calendar dateFromComponents:toDateComponents];

    NSTimeInterval timeIntervalBetweenDates = [adjustedToDate timeIntervalSinceDate:adjustedFromDate];
    NSInteger daysBetweenDates = (NSInteger)(timeIntervalBetweenDates / (60.0 * 60.0 * 24.0));

    NSDateComponents *midnightBeforeFromDateComponents = [[NSDateComponents alloc] init];
    [midnightBeforeFromDateComponents setYear:[fromDateComponents year]];
    [midnightBeforeFromDateComponents setMonth:[fromDateComponents month]];
    [midnightBeforeFromDateComponents setDay:[fromDateComponents day]];

    NSDate *midnightBeforeFromDate = [calendar dateFromComponents:midnightBeforeFromDateComponents];
    [midnightBeforeFromDateComponents release];

    NSDate *midnightAfterFromDate = [[NSDate alloc] initWithTimeInterval:(60.0 * 60.0 * 24.0)
                                                               sinceDate:midnightBeforeFromDate];

    NSTimeInterval timeIntervalBetweenToDateAndMidnightBeforeFromDate = [adjustedToDate timeIntervalSinceDate:midnightBeforeFromDate];
    NSTimeInterval timeIntervalBetweenToDateAndMidnightAfterFromDate = [adjustedToDate timeIntervalSinceDate:midnightAfterFromDate];

    if (timeIntervalBetweenToDateAndMidnightBeforeFromDate < 0.0) {

        // toDate is before the midnight before fromDate

        timeIntervalBetweenToDateAndMidnightBeforeFromDate -= daysBetweenDates * 60.0 * 60.0 * 24.0;

        if (timeIntervalBetweenToDateAndMidnightBeforeFromDate < 0.0)
            daysBetweenDates -= 1;
    }
    else if (timeIntervalBetweenToDateAndMidnightAfterFromDate >= 0.0) {

        // toDate is after the midnight after fromDate

        timeIntervalBetweenToDateAndMidnightAfterFromDate -= daysBetweenDates * 60.0 * 60.0 * 24.0;

        if (timeIntervalBetweenToDateAndMidnightAfterFromDate >= 0.0)
            daysBetweenDates += 1;
    }

    [midnightAfterFromDate release];

    return daysBetweenDates;
}

推荐答案

c $ c> components：fromDate：toDate：options：：

From the docs for components:fromDate:toDate:options::

一个足够小的单元请求保持差异的完全精度。

The result is lossy if there is not a small enough unit requested to hold the full precision of the difference.

由于差异小于一整天，它正确返回结果为0天。

Since the difference is less than a full day, it correctly returns a result of 0 days.

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