我如何计算iOS中的时间？

Question

I don't want to set up a timer that "fires" (and does something) after a certain amount of time has passed.

Therefore, I'm not interested in the NSTimer class and its methods.

All I'm interested in is counting the time that passes by while , for example, some while-loop is executing. I could use NSDate as follows I guess :

NSDate currentDate = [[NSDate alloc] init];

while(someConditionIsTrue)
{
    // executing..
}

timeElapsed = [self timeIntervalSinceDate:currentDate];

NSLog(@"time elapsed was: %i", timeElapsed);

However, if I understand correctly, timeIntervalSinceDate: can only count seconds.

Is there a way I can count the time that is passing by in milliseconds ?

In other words, what is the smallest unit I can count passing time in and how ?

Answer 1

Look at CFAbsoluteTimeGetCurrent()

CFAbsoluteTime before = CFAbsoluteTimeGetCurrent();
CFAbsoluteTime after = CFAbsoluteTimeGetCurrent();

Answer 2

Your second approach is correct. Save the current date in an NSDate object and use timeIntervalSinceDate: to get the passed time since then. The result will be of type NSTimeInterval which is a floating point number. It specifies time differences in seconds, but since it's a floating point number it can store fractions of a second as well.

NSTimeInterval is always specified in seconds; it yields sub-millisecond precision over a range of 10,000 years.