Preferred way to run custom animations

Question

I need to run a complex custom animation in an iOS app. For this, I wrote a function that needs to be called repeatedly and uses the current time-stamp to calculate positions, colors, shadows, etc. of UIView elements on the screen.

There seem to be a whole bunch of different approaches I could use to have this function called:

• Multi-Threading
• Timers
• Dispatch Queues
• God knows what else... :)

I tried calling my animation-function from a separate thread first, but while the thread does run, I don't see any screen updates until I trigger a refresh manually with a device rotation, so I must be missing some step where I call the update functions from inside the GUI Thread instead of my own or invalidating the View or something... But I don't even know if this is the best approach...

What is the preferred way to keep calling a function (for an animation, for example) as quickly as possible (or with a small delay of 10ms or so) without blocking the GUI and in such a way that if this function, for example, changes the background color or position of a view, the screen gets updated?

If possible, I would like to use a method that is as backward-compatible as possible, so preferably something that doesn't use any features introduced in iOS 8.1 (exaggeration)... :)

Aside:

Sorry for not posting a code example. I'm using RoboVM and don't want to "scare off" any answers from true XCode developers. Also, this is more of a general conceptual question rather than a specific bug-fix.

Answer 1

I've found the best performance from CADisplayLink.

displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(displayLinkTick)];
[displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSRunLoopCommonModes];

- (void)displayLinkTick {
  // Update your animation.
}

Don't forget to teardown when you're destroying this view or else you'll have your displayLinkTick called until your application exits:

[displayLink removeFromRunLoop:[NSRunLoop currentRunLoop] forMode:NSRunLoopCommonModes];

Alternatively, if you're using (or convert to) CALayer, your subclass would return YES from needsDisplayForKey: on your animating key. Then, in your CALayer subclass' display method, you'd apply the changes that your self.presentationLayer has for your animation.

@property (assign) CGFloat myAnimatingProperty;

@implementation MyAnimatingLayer : CALayer
+ (BOOL)needsDisplayForKey:(NSString *)key {
  if ([key isEqualToString:@"myAnimatingProperty"]) {
    return YES;
  }
  return [super needsDisplayForKey:key];
}

- (void)display {
  if ([self.animationKeys containsObject:@"myAnimatingProperty"]) {
    CGFloat currentValue = self.presentationLayer.myAnimatingProperty;
    // Update.
  }
}
@end

This second way will allow you to link in with the built-in easing functions really easily.