有没有办法在 CAKeyframeAnimation 完成动画时调用方法？答案

【问题标题】：Is there a way to call a method when a CAKeyframeAnimation finishes animating?有没有办法在 CAKeyframeAnimation 完成动画时调用方法？
【发布时间】：2015-11-24 18:51:19
【问题描述】：

我正在使用 Swift，我需要在 CAKeyframeAnimation 完成后做一些事情。

如果这是UIView，我通常只会使用UIView.animateWithDuration，然后在completionHandler 中实现这些内容，如下所示：

    UIView.animateWithDuration(duration, delay: delay, options: [],
        animations: { },
        completion: {
            (animationFinished: Bool) in

            if animationFinished {
            // DO SOME STUFF IN HERE ONCE THE ANIMATION FINISHES
            }
    })

使用CAKeyframeAnimation 的等效方法是什么？

【问题讨论】：

标签： ios swift nsobject caanimation cakeyframeanimation

【解决方案1】：

我想我想出了如何做到这一点。

这里有一些示例代码可以粘贴到 Xcode 的 Playground 中：

import XCPlayground

class BallAnimation: NSObject { // <- STEP 1 - INHERIT FROM NSOBJECT
  func doMyAnimation() {
    // Make a test background.
    let backgroundView = UIView(frame: CGRect(x: 0, y: 0, width: 400, height: 400))
    XCPlaygroundPage.currentPage.liveView = backgroundView

    // Create the object that will be animated and add it to the background.
    let ballImage = UIImage(named: "ball")
    let ballView = UIImageView(image: ballImage)
    backgroundView.addSubview(ballView)

    // Create the path the object will follow.
    let path = UIBezierPath()
    path.moveToPoint(CGPoint(x: 200, y: 200))
    path.addLineToPoint(CGPoint(x: 200, y:100))

    // Create the animation that will use the path we just created.
    let animation = CAKeyframeAnimation(keyPath: "position")
    animation.path = path.CGPath
    animation.duration = 2.0
    animation.removedOnCompletion = false
    animation.fillMode = kCAFillModeForwards
    animation.delegate = self // <- STEP 2 - SET THE DELEGATE

    // This should start the animation
    ballView.layer.addAnimation(animation, forKey: "animate ball")
  }

  // STEP 3 - OVERRIDE THIS METHOD
  override func animationDidStop(anim: CAAnimation, finished flag: Bool) {
    // When the animation stops it should call this method (make sure the delegate was set above).
    print("Animation did stop.")
  }
}

// Create an instance of the class and call the method that starts the animation.
let ballAnimation = BallAnimation()
ballAnimation.doMyAnimation()

解释

CAAnimation 类将以下方法添加到NSObject：

func animationDidStop(_ anim: CAAnimation, finished flag: Bool)

因此，如果一个类继承自 NSObject，则可以将其设置为 CAKeyframeAnimation 委托，并且可以在动画结束时覆盖 animationDidStop 以执行其他任务。

【讨论】：

【解决方案2】：

我在 XCode 12 中做了类似的事情：

class ViewController: UIViewController, CAAnimationDelegate {

func creatAnimation() {
let animation = CAKeyframeAnimation()
// some code configuring animation
animation.delegate = self
}

func animationDidStop(_ anim: CAAnimation, finished flag: Bool) {
        print("done")
        
 }
}

【讨论】：