(iOS) How to animate rounded rectangle with shapeLayer? - ios

Question

I am trying to animate the width of a rounded rectangle, the problem is when going from bigger width to thinner width, the animation does an "aberration ease jump".
Here's the code:
shapeLayer = [CAShapeLayer layer];
shapeRect = CGRectMake(0.0f, 0.0f, 150.0f, 200.0f);
[shapeLayer setBounds:shapeRect];
[shapeLayer setPosition:CGPointMake(iniPosX, 80.0f)];
[shapeLayer setFillColor:[[UIColor blackColor] CGColor]];
[shapeLayer setStrokeColor:[[UIColor clearColor] CGColor]];
[shapeLayer setLineWidth:1.0f];
[shapeLayer setLineJoin:kCALineJoinRound];
[shapeLayer setOpacity:0.2];
path = [UIBezierPath bezierPathWithRoundedRect:shapeRect cornerRadius:15.0];
[shapeLayer setPath:path.CGPath];
[self.layer addSublayer:shapeLayer];
And when I start the animation:
- (void)adjustSelectorToPosAndSize:(float)posX andWidth:(float)width
{
shapeRect = CGRectMake(0.0f, 0.0f, width, 200.0f);
[shapeLayer setBounds:shapeRect];
[shapeLayer setPosition:CGPointMake(posX, 80.0f)];
path = [UIBezierPath bezierPathWithRoundedRect:shapeRect cornerRadius:15.0];
[shapeLayer setPath:path.CGPath];
}
What am I doing wrong?

Answer 1

Doing this with a CAShapeLayer seems overly complicated to me if you are only using it for a rounded rectangle. Why not simply use a CALayer with the cornerRadius properly set?
Animating the frame with cornerRadius set will work fine.
myLayer = [CALayer layer];
shapeRect = CGRectMake(0.0f, 0.0f, 150.0f, 200.0f);
[myLayer setBounds:shapeRect];
[myLayer setPosition:CGPointMake(iniPosX, 80.0f)];
[myLayer setBackgroundColor:[[UIColor blackColor] CGColor]];
[myLayer setBorderColor:[[UIColor clearColor] CGColor]];
[myLayer setBorderWidth:1.0f];
[myLayer setOpacity:0.2];
[myLayer setCornerRadius:15.0];
[self.layer addSublayer:myLayer];
Animating it is done by simply chaining the frame (not the path)
- (void)adjustSelectorToPosAndSize:(float)posX andWidth:(float)width
{
shapeRect = CGRectMake(0.0f, 0.0f, width, 200.0f);
[myLayer setBounds:shapeRect];
[myLayer setPosition:CGPointMake(posX, 80.0f)];
}
Important:
Some of the properties changed name like fillColor became backgroundColor and the strokeColor and lineWidth became borderColor and borderWidth etc.

Answer 2

Although CAShapeLayer’s path property is animatable, it does not do so implicitly like bounds and position, you have to make an explicit animation:
CABasicAnimation* anim = [CABasicAnimation animationWithKeyPath: #"path"];
anim.fromValue = (id) fromPath.CGPath;
anim.toValue = (id) toPath.CGPath;
anim.duration = 1.0;
[layer addAnimation: anim forKey: #“resize”];
Since you probably want all three animations to happen together, you can make them all explicit and grouped together:
CABasicAnimation* anim1 = [CABasicAnimation animationWithKeyPath: #"position"];
anim1.fromValue = [NSValue valueWithCGPoint: fromPosition];
anim1.toValue = [NSValue valueWithCGPoint: toPosition];
anim1.duration = 1.0;
CABasicAnimation* anim2 = [CABasicAnimation animationWithKeyPath: #"bounds"];
anim2.fromValue = [NSValue valueWithCGRect: fromBounds];
anim2.toValue = [NSValue valueWithCGRect: toBounds];
anim2.duration = 1.0;
CABasicAnimation* anim3 = [CABasicAnimation animationWithKeyPath: #"path"];
anim3.fromValue = (id) fromPath.CGPath;
anim3.toValue = (id) toPath.CGPath;
anim3.duration = 1.0;
CAAnimationGroup* animG = [CAAnimationGroup animation];
animG.animations = [NSArray arrayWithObjects: anim1, anim2, anim3, nil];
animG.duration = 1.0;
[layer addAnimation: animG forKey:#"resize"];
If your shape does not have contents or children then you may be able to use a CALayer instead:
CALayer* rectLayer = [CALayer layer];
rectLayer.masksToBounds = YES;
rectLayer.bounds = startBounds;
rectLayer.backgroundColor = [[UIColor blackColor] CGColor];
rectLayer.cornerRadius = 15.0;
[self.layer addSublayer: rectLayer];
// Then later implicitly animate the bounds:
rectLayer.bounds = newBounds;