Class

CATransition

An object that provides an animated transition between a layer's states.

Declaration

class CATransition : CAAnimation

Overview

You can transition between a layer's states by creating and adding a CATransition object to it. The default transition is a cross fade, but you can specify different effects from a set of predefined transitions.

Listing 1 shows how you can transition between the two states of a CATextLayer named transitioningLayer. When the layer is first created, its backgroundColor is set to red and its string property is set to Red. When the runTransition() function is called, a new CATransition object is created and added to transitioningLayer, and the state of the layer is changed so that its background color is blue and its rendered text reads Blue.

The end result is that the push transition animates the red state from left to right with the blue state entering the scene from the left.

Listing 1

Transitioning between a layer's states

let transitioningLayer = CATextLayer()
     
override func viewDidLoad() {
    super.viewDidLoad()
    transitioningLayer.frame = CGRect(x: 10, y: 10,
                                      width: 320, height: 160)
    
    view.layer.addSublayer(transitioningLayer)
    
    // Initial "red" state
    transitioningLayer.backgroundColor = UIColor.red.cgColor
    transitioningLayer.string = "Red"
}
      
   
func runTransition() {
    let transition = CATransition()
    transition.duration = 2
    
    transition.type = kCATransitionPush
    
    transitioningLayer.add(transition,
                           forKey: "transition")
    
    // Transition to "blue" state
    transitioningLayer.backgroundColor = UIColor.blue.cgColor
    transitioningLayer.string = "Blue"
}