我正在为iPhone编写一款GTD应用程序。对于到期的任务,我想显示类似于“明天到期”、“昨天到期”或“7月18日到期”的内容。显然,即使任务还有不到24小时的时间(例如,用户在周六晚上11点检查并看到周日早上8点有一个任务),我也需要显示“明天”。因此,我编写了一个获取两个日期之间天数的方法。以下是代码...
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]);
... 这是输出结果:
NSDate *nowDate = 2010-01-01 15:00:00 -0700
NSDate *dueDate = 2010-01-02 14:00:00 -0700
Days between dates: 0
从结果可以看出,这个方法返回的结果不正确。根据这两个日期之间的天数应该是1,但是它返回的却不是。我做错了什么呢?
编辑:我写了另外一个方法。虽然我没有进行详尽的单元测试,但目前来看似乎是有效的:
+ (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;
}