Timer-Based Animation - iOS Core Animation - page 238

//apply easing
time = bounceEaseOut(time);
//interpolate position
id position = [ self interpolateFromValue: self .fromValue
toValue: self .toValue
time:time];
//move ball view to new position
self .ballView.center = [position CGPointValue];
//stop the timer if we've reached the end of the animation
if ( self .timeOffset >= self .duration)
{
[ self .timer invalidate];
self .timer = nil ;
}
}
@end
Run Loop Modes
Notice that when we create the CADisplayLink , we are required to specify a run loop and
run loop mode. For the run loop, we've used the main run loop (the run loop hosted by the
main thread) because any user interface updates should always be performed on the main
thread. The choice of mode is less clear, though. Every task that is added to the run loop has
a mode that determines its priority. To ensure that the user interface remains smooth at all
times, iOS will give priority to user interface related tasks and may actually stop executing
other tasks altogether for a brief time if there is too much UI activity.
A typical example of this is when you are scrolling using a UIScrollView . During the
scroll, redrawing the scrollview content takes priority over other tasks, so standard NSTimer
and network events may not fire while this is happening. Some common choices for the run
loop mode are as follows:
▪ NSDefaultRunLoopMode —The standard priority
▪ NSRunLoopCommonModes —High priority
▪ UITrackingRunLoopMode —Used for animating UIScrollView and other controls
In our example, we have used NSDefaultRunLoopMode , but to ensure that our animation
runs smoothly, we could use NSRunLoopCommonModes instead. Just be cautious when using
this mode because when your animation is running at a high frame rate, you may find that