objective-c - iOS:比较两个没有时间部分的 NSDate-s

Question

我想比较两个日期:date1 和 date2

2011-06-06 12:59:48.994 Project[419:707] firstDate:2011-06-06 10:59:21 +0000
2011-06-06 12:59:49.004 Project[419:707] selectedData:2011-06-06 10:59:17 +0000

但是这些日期有不同的时间，当我使用 NSOrderedSame 时它不能正常工作，我该如何解决？

我的代码:

NSDate *firstDate = [[appDelegate.project objectAtIndex:i]objectAtIndex:3];
NSDate *secondDate = [[appDelegate.project objectAtIndex:i]objectAtIndex:4];

NSCalendar *calendar = [NSCalendar currentCalendar];
NSInteger comps = (NSDayCalendarUnit | NSMonthCalendarUnit | NSYearCalendarUnit);

NSDateComponents *date1Components = [calendar components:comps 
                                                            fromDate:firstDate];
NSDateComponents *date2Components = [calendar components:comps 
                                                            fromDate:secondDate];
NSDateComponents *date3Components = [calendar components:comps fromDate:appDelegate.selectedDate];

NSLog(@"firstDate:%@", [date1Components date]);
NSLog(@"secondDate:%@", [date2Components date]);
NSLog(@"selectedData:%@", [date3Components date]);

NSComparisonResult compareStart = [[date1Components date] compare: [date3Components date]]; 
NSComparisonResult compareEnd = [[date2Components date] compare: [date3Components date]]; 

if ((compareStart == NSOrderedAscending || compareStart == NSOrderedSame)
     && (compareEnd == NSOrderedDescending || compareEnd == NSOrderedSame))

{
    NSLog(@"inside");

然后我想在 date1 <= selectedDate <= date2 时比较我的日期和“if”中的条目；现在我明白了，因为我有一个警告:我应该添加这个“[date1Components date]”并且它有效；问题是我在 NSLog 中有空值，为什么？？

Answer 1

NSCalendar *calendar = [NSCalendar currentCalendar];
NSInteger comps = (NSCalendarUnitDay | NSCalendarUnitMonth | NSCalendarUnitYear);

NSDateComponents *date1Components = [calendar components:comps 
                                                fromDate: date1];
NSDateComponents *date2Components = [calendar components:comps 
                                                fromDate: date2];

date1 = [calendar dateFromComponents:date1Components];
date2 = [calendar dateFromComponents:date2Components];

NSComparisonResult result = [date1 compare:date2];
if (result == NSOrderedAscending) {
} else if (result == NSOrderedDescending) {
}  else {
    //the same
}

---

还有另一种方便的方法可以为给定日期创建代表给定单元开始的日期:[aCalendar rangeOfUnit:startDate:interval:forDate:]
要说明此方法的工作原理，请参阅此代码，它可以轻松地为给定日期(此处:现在)创建一天、一周、一个月和一年的开始日期。

NSDate *now = [NSDate date];
NSDate *startOfToday = nil;
NSDate *startOfThisWeek = nil;
NSDate *startOfThisMonth = nil;
NSDate *startOfThisYear = nil;
[[NSCalendar currentCalendar] rangeOfUnit:NSDayCalendarUnit startDate:&startOfToday interval:NULL forDate:now];
[[NSCalendar currentCalendar] rangeOfUnit:NSWeekCalendarUnit startDate:&startOfThisWeek interval:NULL forDate:now];
[[NSCalendar currentCalendar] rangeOfUnit:NSMonthCalendarUnit startDate:&startOfThisMonth interval:NULL forDate:now];
[[NSCalendar currentCalendar] rangeOfUnit:NSYearCalendarUnit startDate:&startOfThisYear interval:NULL forDate:now];

NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateStyle:NSDateFormatterFullStyle];
[formatter setTimeStyle:NSDateFormatterFullStyle];

NSLog(@"%@", [formatter stringFromDate:now]);
NSLog(@"%@", [formatter stringFromDate:startOfToday]);
NSLog(@"%@", [formatter stringFromDate:startOfThisWeek]);
NSLog(@"%@", [formatter stringFromDate:startOfThisMonth]);
NSLog(@"%@", [formatter stringFromDate:startOfThisYear]);

结果:

Thursday, July 12, 2012, 4:36:07 PM Central European Summer Time 
Thursday, July 12, 2012, 12:00:00 AM Central European Summer Time 
Sunday, July 8, 2012, 12:00:00 AM Central European Summer Time 
Sunday, July 1, 2012, 12:00:00 AM Central European Summer Time 
Sunday, January 1, 2012, 12:00:00 AM Central European Standard Time

这使我们能够将第一个代码缩短为:

[[NSCalendar currentCalendar] rangeOfUnit:NSDayCalendarUnit startDate:&date1 interval:NULL forDate:date1];
[[NSCalendar currentCalendar] rangeOfUnit:NSDayCalendarUnit startDate:&date2 interval:NULL forDate:date2];

NSComparisonResult result = [date1 compare:date2];
if (result == NSOrderedAscending) {
} else if (result == NSOrderedDescending) {
}  else {
    //the same
}

请注意，在这段代码中，date1 和 date2 将被覆盖。或者，您可以传递对 startDate 的另一个 NSDate 指针的引用，如上面的代码所示，其中 now 保持不变。