How to reuse an CABasicAnimation when not removed

问题:

Lots of people are talking about keeping an CABasicAnimation object around after it has been used.

So by setting

removedOnCompletion = NO

the animation object keeps attached to the layer when the animation is complete. How would I re-launch this animation again without creating a new CABasicAnimation?

What's the point of keeping this object around? The only benefit I know is that we can set removedOnCompletion = NO and set kCAFillModeForwards so that Core Animation does not revert the visual representation back to the model values in the CALayer.

But how to re-use the animation, like everyone is talking about?

回答1:

Try this:

1. Add the animation with a key using [layer addAnimation:myAnimation forKey:@"myKey"]

2. To get a reference to it later, call [layer animationForKey:@"myKey"]

3. Read this note from Apple which explains how to pause and resume (restart) animations.

回答2:

This worked for me but I am sure someone will tell me the value is already stored in a key..

When I created a layer and assigned an animation to it I set the animation to a keyed value associated with the layer.

in this example layersCurrentAnimation is the CABasicAnimation and myAnimatedLayer is a CALayer.

[myAnimatedLayer setValue:layersCurrentAnimation forKey:@"basicAnimation"]

then if the animation was to stop I would get the animation value out from the layer and re-run it

CABasicAnimation *thisAnimation = [myAnimatedLayer  valueForKey:@"basicAnimation"];

[myAnimatedLayer addAnimation:thisAnimation forKey:nil];