Core animation code structure/conventions

Question

In learning Core Animation, I learned very quickly that if you don't do it right, you get really weird undefined behavior. To that end, I have a few questions that will help me conceptually understand it better.

• My NSView subclass declares the following in it's init. This view is a subview of normal layer backed view.

  [self setLayer:[CALayer layer]];
  [self setWantsLayer:NO];
  

  After this, when and in what situations should I refer to self as opposed to [self layer]? I have been ONLY manipulating the layer with explicit and implicit animations, staying away from [self setFrame:] etc. and using [[self layer] setPosition] etc.

• The problem with this approach is that the actual frame of the view stays in one spot throughout any and all animations applied. What if my view is supposed to recieve mouse events? For example, I have a view that uses core animation and it is dragged around by the mouse. Is there a way I can somehow keep the view frame synced with the current state of the presentation layer so I can receive proper mouse events?

• About the presentation layer, apparently it's only available when an actual animation is in progress. Is there any sort of property of the layer that can tell me where it's ACTUALLY visually at even when an animation's not in progress?

Answer 1

Firstly, you want to use [self setWantsLayer: YES]. Also, it's only important to call -setLayer: before -setWantsLayer: if you want to provide a specific CALayer subclass (such as a CAScrollLayer); if you just want a regular CALayer you just call -setWantsLayer: and it'll be created for you. Even better, just check the 'wants layer' option in Interface Builder.

Secondly, the entire point of using a layer-backed view is that you can continue to use the regular NSView methods and get the free CoreAnimation 'tweening' effects. If you want to use CoreAnimation as your only means of moving items around, then the correct way to do so is to create a layer backed view which contains your pure-CALayer presentation hierarchy.

I've not looked at any freely-available CoreAnimation tutorials, but I can definitely recommend the Pragmatic Programmers' book on the subject. They also have a screencast available by the book's author.

Answer 2

I think you need to re-phrase your question a little. It seems there is some underlying misunderstanding, but you're not really expressing it very clearly. You're question title suggests you're looking to understand something more theoretical, but your actual question suggests you're looking for something more concrete. Let me see if I can clarify a few things.

• The presentationLayer provides information about the layer's current state while "in-flight".

• When there is no animation occurring, the presentationLayer and the layer information will be identical. Query the layer's bounds, frame, or position to find out where it is currently in its parents coordinate space.

• NSViews must have layer backing enabled to be able to perform animations.

• Make sure you're not just animating with an explicit animation and not actually setting the layer value that you're animating. Animations don't automatically change the properties of the layers they're animating. You have to change the property to the ending value yourself or it will just "snap back" to the starting value.

• If you want to animate the view, as opposed to a layer, you can use the animator proxy, like [[view animator] setFrame:newFrame];

• Wrap calls to the animator in a CATrasaction to alter things like animation duration.

Let me know if you need some clarification by updating your question. Providing some pertinent code would really help identify the problems you're having trouble solving.