Getting the time elapsed (Objective-c)

Question

I need to get time that elapsed between two events: for example between appearance of UIView and between user's first reaction.

Answer 1

NSDate *start = [NSDate date];
// do stuff...
NSTimeInterval timeInterval = [start timeIntervalSinceNow];

timeInterval is the difference between start and now, in seconds, with sub-millisecond precision.

Answer 2

use the timeIntervalSince1970 function of the NSDate class like below:

double start = [startDate timeIntervalSince1970];
double end = [endDate timeIntervalSince1970];
double difference = end - start;

basically, this is what i use to compare the difference in seconds between 2 different dates. also check this link here

Answer 3

For percise time measurements (like GetTickCount), also take a look at mach_absolute_time and this Apple Q&A: http://developer.apple.com/qa/qa2004/qa1398.html.

Answer 4

Use the timeIntervalSinceDate method

NSTimeInterval secondsElapsed = [secondDate timeIntervalSinceDate:firstDate];

NSTimeInterval is just a double, define in NSDate like this:

typedef double NSTimeInterval;