Animate frame property using CABasicAnimation

Question

I'm trying to make an exact "translation" of this UIView block-based animation code:

[UIView animateWithDuration:0.5
                      delay:0.0
                    options:UIViewAnimationOptionCurveEaseInOut
                 animations:^{
                               someView.frame = CGRect(0, 100, 200, 200);
                             }
                 completion:nil];

using CABasicAnimation instead.

I'm totally aware that the frame property is actually a combination of position, bounds and anchorPoint of the underlying layer, as it is described here: http://developer.apple.com/library/mac/#qa/qa1620/_index.html
... and I already made a solution like that, using two CABasicAnimations one setting the position, one for bounds and it works for that one view.

The problem is however that I have subviews inside my view. someView has a subview of type UIScrollView in which I place still another subview of type UIImageView. UIScrollView subview has autoresizingMask set to UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight. That all works perfectly if I use the UIView block-based version, however when I try using CABasicAnimations the subviews start behaving unexpectedly(i.e. get resized to incorrect widths). So it seems autoresizingMask is not working correctly when using CABasicAnimations. I noticed also that subviews don't receive a call to setFrame:, although the frame property of the parent view does change after changes to layer position and bounds are made.

That's why I would like to know what would be the correct code to replicate with CABasicAnimation that what is happening when one uses UIView's animateWithDuration method.

Answer 1

I'm totally aware that the frame property is actually a combination of position, bounds and anchorPoint of the underlying layer

Good, but it's important also to be aware that frame is not an animatable property for layers. If you want to animate with CABasicAnimation you must use properties that are animatable for layers. The CALayer documentation marks every such property as explicitly "animatable". The idea of using bounds and position is correct.

Thus, this code does essentially what you were doing before:

[CATransaction setDisableActions:YES];
// set final bounds and position
v.layer.bounds = CGRectMake(0,0,200,200);
v.layer.position = CGPointMake(100,200);

// cause those changes to be animated
CABasicAnimation* a1 = [CABasicAnimation animationWithKeyPath:@"bounds"];
a1.duration = 0.5;
CABasicAnimation* a2 = [CABasicAnimation animationWithKeyPath:@"position"];
a2.duration = 0.5;
[v.layer addAnimation:a1 forKey:nil];
[v.layer addAnimation:a2 forKey:nil];

However, that code has no effect on the size of any sublayers of v.layer. (A subview of v is drawn by a sublayer of v.layer.) That, unfortunately, is the problem you are trying to solve. I believe that by dropping down to the level of layers and direct explicit core animation, you have given up autoresizing, which happens at the view level. Thus you will need to animate the sublayers as well. That is what view animation was doing for you.

This is an unfortunate feature of iOS. Mac OS X has layer constraints (CAConstraint) that do at the layer level what autoresizing does at the view level (and more). But iOS is missing that feature.