在alpha上平滑地暂停重复的UIView块动画，然后再播放另一个动画

import UIKit

class AnimatedView: UIView {
    
    private var displayLink: CADisplayLink?
    private var startTime: CFTimeInterval = 0
    private var pausedTimeOffset: CFTimeInterval = 0
    private var animationDuration: TimeInterval = 2.0
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        setupAnimation()
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        setupAnimation()
    }
    
    private func setupAnimation() {
        displayLink = CADisplayLink(target: self, selector: #selector(updateAnimation))
        displayLink?.add(to: .current, forMode: .common)
    }
    
    @objc private func updateAnimation(displayLink: CADisplayLink) {
        if startTime == 0 {
            startTime = displayLink.timestamp - pausedTimeOffset
        }
        
        let elapsed = displayLink.timestamp - startTime
        let progress = CGFloat(fmod(elapsed, animationDuration) / animationDuration)
        
        alpha = 0.5 + 0.5 * sin(progress * .pi * 2)
    }
    
    func pauseAnimation() {
        if !displayLink?.isPaused ?? true {
            displayLink?.pause()
            pausedTimeOffset = CACurrentMediaTime() - startTime
        }
    }
    
    func resumeAnimation() {
        if displayLink?.isPaused ?? false {
            startTime = CACurrentMediaTime() - pausedTimeOffset
            displayLink?.resume()
        }
    }
    
    func startNewAnimation() {
        pauseAnimation()
        // 设置新的动画参数
        animationDuration = 3.0
        startTime = 0
        displayLink?.resume()
    }
}