iOS NSTimeInterval from dates wrong

Question

I'm calculating the duration time between a startTime and endTime and am using the following code to get the time interval between two NSDates

    NSTimeInterval duration = [self.endTime timeIntervalSinceDate:self.startTime];
    NSLog(@"interval: %f", duration);

However, the NSLog statement tells me that the duration is wrong. The dates are derived from a datePicker. For example, when I set the start date to Jun 19, 2013 9:15pm and end date to Jun 19, 2013, 2013 916pm (one minute later), the duration logged is 15.00000 instead of 60.00000.

Why is this? How can I get the correct duration between two dates?

EDIT

I did some more logging and logged the start date and the end time. Here's the NSLog statement

NSLog(@"interval: %f for %@ to %@", duration, self.startTime, self.endTime);

and here's what gets logged:

interval: 15.000000 for 2013-06-19 04:52:45 +0000 to 2013-06-19 04:53:00 +0000

For some reason the start date from the datePicker is setting the seconds to 45 even though the date picker just says 4:52. How can I fix this?

Also, as a note, the same datePicker is used to choose both dates if that matters at all.

Update your log statement to also log self.endTime and self.startTime. Update your question with the actual output from this updated log statement. — rmaddy
Those two times are 15 seconds apart. Why do you expect a different result? — rmaddy
@rmaddy after logging the start and end time, I realized my problem is not actually the duration but the dates set by the datePicker. Any idea how to get it to return a date with 0 seconds? I'm not sure why the datePicker gives a date with 45 seconds at one time and 0 seconds at another time. — user1529956

rmaddy rmaddy · Accepted Answer · 2013-06-19T18:56:39

The issue actually appears to be a "feature" of UIDatePicker when selecting a time. Even though it only shows hours and minutes, the time includes whatever the current seconds happen to be. Personally I think this is a bug in the date picker.

Your best solution is to tweak the value that you get back from the date picker.

Here's one way to ensure the date has 0 seconds:

- (NSDate *)truncateSeconds:(NSDate *)pickerDate {
    NSTimeInterval secs = [pickerDate timeIntervalSinceReferenceDate];
    long truncated = secs / 60 * 60;

    return [NSDate dateWithTimeIntervalSinceReferenceDate:truncated];
}

iOS NSTimeInterval from dates wrong

1 Answers