Adding scale animation for CAShapeLayer - ios

Question

I'd like to implement transition animation between two UIView according to the material design as shown on screenshot below (first part of animation only):
But I'd like to make it more realistic with applying animated mask to UIView. Here is a code I've developed:
- (IBAction)onButtonTapped:(UIButton *)sender
{
// 1. make a hole in self.view to make visible another view
UIBezierPath *maskPath = [UIBezierPath bezierPathWithRect:self.view.bounds];
[maskPath appendPath:[UIBezierPath bezierPathWithArcCenter:sender.center
radius:sender.frame.size.width/2.0f
startAngle:0.0f
endAngle:2.0f*M_PI
clockwise:NO]];
CAShapeLayer *maskLayer = [CAShapeLayer layer];
maskLayer.fillRule = kCAFillRuleEvenOdd;
maskLayer.fillColor = [UIColor blackColor].CGColor;
maskLayer.path = maskPath.CGPath;
// 2. add scale animation for resizing hole
CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:#"transform.scale"];
animation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
animation.fromValue = [NSValue valueWithCGRect:sender.frame];
animation.toValue = [NSValue valueWithCGRect:self.view.bounds];
animation.duration = 3.0f;
[maskLayer addAnimation:animation forKey:#"scaleAnimation"];
self.view.layer.mask = maskLayer;
}
My idea is adding a "hole" into modal UIView and then scale wit animation.
The problem is that it doesn't work properly. First part of code make a hole well. But scaling animation of a hole doesn't work at all.

Answer 1

You can't add an animation to a layer if the layer isn't in some window's layer tree. You need to do things in this order:
self.view.layer.mask = maskLayer;
[CATransaction flush];
[maskLayer addAnimation:animation forKey:#"scaleAnimation"];