Timestamp. Difference between two times

Question

I'm trying to make a timestamp-app where you capture the times with one button.

When the button is pressed it prints out the current time 00:00:00. When the button is pressed the second time it prints out the current time again (i.e 00:00:15).

I then want it to calculate the difference in time between the two timestamps (10 seconds).

I am new to objective-c and I have been sitting with this tiny problem for hours. Would be nice to have a pointer in the right direction.

I'm having problems with the timeIntervalSinceDate. Here is the code:

- (IBAction)checkButton:(id)sender {


if (buttonPress) {

    self.checkInStamp = [NSDate date];

    NSDateFormatter *timeFormatter = [[NSDateFormatter alloc] init];
    [timeFormatter setTimeStyle:NSDateFormatterMediumStyle];

    checkInTime.text = [timeFormatter stringFromDate:checkInStamp];
    buttonPress = false;
}
    else {

        self.checkOutStamp = [NSDate date];

        NSDateFormatter *timeFormatter = [[NSDateFormatter alloc] init];
        [timeFormatter setTimeStyle:NSDateFormatterMediumStyle];

        checkOutTime.text = [timeFormatter stringFromDate:checkOutStamp];

        NSTimeInterval timeDifference = [checkOutStamp timeIntervalSinceDate:checkInStamp];

        totalDuration.text = @"%d", timeDifference; //<-This gives "Expression result unused on build"
    }
}

Thank you for any help!

Answer 1

The difference between two NSDate objects is obtained using the [NSDate timeIntervalSinceDate:] method (reference) and is expressed as a NSTimeInterval (a typedef'd double):

NSTimeInterval difference = [self.checkOutStamp timeIntervalSinceDate:self.checkInStamp];
NSLog(@"Difference is %f seconds", difference);