Comparing two dates with nsdate

问题

In my app I have to compare two times: current (which is 12:44) and given I tried:

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"hh:mm"];
NSDate *neededDate = [[NSDate alloc] init];
neededDate = [dateFormatter dateFromString:@"14:45"];
if ([neededDate compare:[NSDate date]] == NSOrderedAscending) {
NSLog(@"yes");
} else NSLog(@"no");
[neededDate release];
[dateFormatter release];

But any time I launch it, NSLog says "no". Please, suggest where I' m wrong. Thank you in advance.

回答1:

Because your neededDate will be equal to "1970/01/01 14:45".

You need to set correct year and date.

You can get current year, month and say, for example, using next approach:

NSDateComponents *components = [[NSCalendar currentCalendar] components:NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit fromDate:[NSDate date]];
NSLog(@"Current year: %d", components.year);
NSLog(@"Current month: %d", components.month);
NSLog(@"Current day: %d", components.day);

回答2:

I think the problem is here:

[dateFormatter setDateFormat:@"hh:mm"];

should be:

[dateFormatter setDateFormat:@"HH:mm"];

because now for "14:45" it returns (null) date

(this is additionally to previous answer :)

回答3:

it means that in your case, neededDate is always higher than the current date. this is probably because you store a 48 hour string in a 24 hour format. change the string to HH:mm

also, verify the value you store in neededDate.

here's a small example

NSDate *neededDate = [[NSDate date] dateByAddingTimeInterval:5];
    if ([neededDate compare:[NSDate date]] == NSOrderedAscending) {
        NSLog(@"asc");
    } else {
        NSLog(@"dec");
    }

in this case, dec will be printed.

来源：https://stackoverflow.com/questions/7901061/comparing-two-dates-with-nsdate

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iphone

ios

nsdate