CATransition type fade seems broken - ios

Question

When working on this question, I notice that maybe fade of CATransitionType in CATransition is not working or broken. The rest of CATransitionType: moveIn, push, reveal works correctly.
I'm working on iPhone 13, iOS 16.0.
Code of the transition:
extension CALayer {
func makeFadeTransition() {
let transition = CATransition()
transition.timingFunction = CAMediaTimingFunction(name: .easeInEaseOut)
transition.duration = 0.5
transition.type = .fade
self.add(transition, forKey: nil)
}
}
Usage:
self.customView.layer.makeFadeTransition()
I know that we can switch to using UIView.animate combined with alpha to change opacity instead.
UIView.animate(withDuration: 0.15, animations: {
self.customView.alpha = 0.0
})
or using CABasicAnimation:
extension CALayer {
func makeFadeTransition() {
let transition = CABasicAnimation(keyPath: "opacity")
transition.timingFunction = CAMediaTimingFunction(name: .easeInEaseOut)
transition.duration = 0.5
transition.fromValue = 1.0
transition.toValue = 0.0
self.add(transition, forKey: nil)
}
}
But again, is CATransitionType type fade broken, or am I wrong at something?

Answer 1

You have to do something to change the layer...
For example, to fade-out / fade-in, we could do this:
extension CALayer {
func makeFadeTransition() {
let transition = CATransition()
transition.timingFunction = CAMediaTimingFunction(name: .easeInEaseOut)
// let's use duration of 2.5 to make it more obvious
transition.duration = 2.5
transition.type = .fade
// change the layer... opacity, backgroundColor, frame, etc
// fade transition doesn't like opacity of 0.0, so we'll use 0.01
self.opacity = self.opacity == 1.0 ? 0.01 : 1.0
// or, for example,
// "shrink" the layer by 20-points
//self.frame = self.frame.insetBy(dx: 20.0, dy: 20.0)
self.add(transition, forKey: nil)
}
}