Question

I am trying to create an NSTimer that counts up from 00:00:00 to whenever the user presses stop. I have created an NSDateInterval of 1 second, but I can’t get it to count up from 00:00:00, only the current date or a date that I set.

What is the best way to do this? And is NSTimer the best way to do this or should I just get the difference between the time the user presses the first button ([NSDate date] to set it) and the time at that second (a selector fired off by NSTimer)? I want to make sure there is as little accuracy fault as possible, and I am aware of NSTimer‘s problems with accuracy sometimes.

Answer 1

Save the time the timer starts with [NSDate date], and then record the time it stops as well. The display time will be the difference, displayed as you listed. The NSTimer will be used just to trigger an update, and you can set the interval fairly small, say 1/10th of a second. Something like:

[NSTimer scheduledTimerWithTimeInterval: 0.1f target: self 
    selector: @selector(updateTimeDisplay) userInfo: nil repeats: YES];