CAAnimation completion callback block

It’s really useful to fire a function when an animation is complete.
There’s no built in way to do that in CoreAnimation, it does have the concept of delegate’s, which get you half way there.

However if you have multiple animations firing, and your delegate is catching everything, you’re gonna be in for a world of hurt.

Here is a simple Swift class I wrote to extend CAAnimation to accept onStart/onCompletion blocks:

Updated to Swift 4 by https://gist.github.com/dagronf

//
//  CAAnimation+BlockCallback.swift
//

import UIKit

//
// Modified from http://onedayitwillmake.com/blog/2016/06/caanimation-completion-callback-block/
// Updated for Swift 4 syntax
// All credit to the original author (Mario Gonzalez)
//
// USAGE:
//
//  var animation = CABasicAnimation(keyPath: "strokeEnd")
//  animation.duration = duration
//  animation.fromValue = 0.0
//  animation.toValue = 1.0
//  animation.startBlock { startingAnimation, status in
//    print("Starting...")
//  }
//  animation.completionBlock { completingAnimation, status in
//    print("Completed!")
//  }

public typealias CAAnimationBlockCallback = (CAAnimation, Bool) -> ();

public class CAAnimationBlockCallbackDelegate: NSObject, CAAnimationDelegate {
   var onStartCallback: CAAnimationBlockCallback?
   var onCompleteCallback: CAAnimationBlockCallback?

   public func animationDidStart(_ anim: CAAnimation) {
      if let startHandler = onStartCallback {
         startHandler(anim, true)
      }
   }

   public func animationDidStop(_ anim: CAAnimation, finished flag: Bool) {
      if let completionHandler = onCompleteCallback {
         completionHandler(anim, flag);
      }
   }
}

public extension CAAnimation {
   // See if there is already a CAAnimationDelegate handling this animation
   // If there is, add onStart to it, if not create one
   func startBlock(callback: @escaping CAAnimationBlockCallback) {
      if let myDelegate = self.delegate as? CAAnimationBlockCallbackDelegate {
         myDelegate.onStartCallback = callback;
      } else {
         let callbackDelegate = CAAnimationBlockCallbackDelegate()
         callbackDelegate.onStartCallback = callback
         self.delegate = callbackDelegate
      }
   }

   // See if there is already a CAAnimationDelegate handling this animation
   // If there is, add onCompletion to it, if not create one
   func completionBlock(callback: @escaping CAAnimationBlockCallback) {
      if let myDelegate = self.delegate as? CAAnimationBlockCallbackDelegate {
         myDelegate.onCompleteCallback = callback
      } else {
         let callbackDelegate = CAAnimationBlockCallbackDelegate()
         callbackDelegate.onCompleteCallback = callback
         self.delegate = callbackDelegate
      }
   }
}

CAAnimation delegate not working (Swift)

CAAnimation provides a way of receiving a callback upon start or completion of an animation.
If you have a ‘pure’ class, that is a class that does not inherit from anything, doing this will have no effect:


class Petal { func startAnimation(duration: Double = 2.0) { let pathAnimation = CABasicAnimation(keyPath: "strokeEnd"); pathAnimation!.delegate = self; pathAnimation!.duration = duration; pathAnimation!.fromValue = 0.0; pathAnimation!.toValue = 1.0; self.shapeLayer.addAnimation(pathAnimation!, forKey: "strokeEnd"); } func animationDidStart(anim: CAAnimation) { Swift.print("ANIMATION DID START!"); } func animationDidStop(anim: CAAnimation, finished flag: Bool) { Swift.print("ANIMATION DID END!"); } }

The reason is because:
You must subclass NSObject, as the delegate methods exist as an informal protocol extension on NSObject

So simply changing it to this is enough:


class Petal:NSObject { // Subclass NSObject func startAnimation(duration: Double = 2.0) { .... } // These are now overrides override func animationDidStart(anim: CAAnimation) { Swift.print("ANIMATION DID START!"); } override func animationDidStop(anim: CAAnimation, finished flag: Bool) { Swift.print("ANIMATION DID END!"); } }