UIViewPropertyAnimator isReversed 不更新视图转换

Question

我有一个观点，我想通过以下方式制作动画：

• 使用

  CGAffineTransform

更改视图变换Y比例缩小到0
• 更改视图背景颜色和缩放视图转换回.identity

因为我想重用相同的缓动函数，所以我想只有一个

UIViewPropertyAnimator

并使用它的

isReversed

属性。

然而，当我尝试这个时，结果在屏幕上看起来不错，但内部比例保持在 0.

这是一个简单的 ViewController，它复制了这个问题：

import UIKit
import Combine

class ViewController: UIViewController {
    private var testView: UIView = {
        let view = UIView()
        view.backgroundColor = .red
        return view
    }()

    private lazy var scaleAnimator = UIViewPropertyAnimator(duration: 2,
                                                            controlPoint1: CGPoint(x: 0.36, y: 0),
                                                            controlPoint2: CGPoint(x: 0.66, y: -0.56))
    private var cancellables = Set<AnyCancellable>()

    override func viewDidLoad() {
        super.viewDidLoad()

        view.addSubview(testView)
        testView.translatesAutoresizingMaskIntoConstraints = false

        NSLayoutConstraint.activate([
            testView.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            testView.centerYAnchor.constraint(equalTo: view.centerYAnchor),
            testView.widthAnchor.constraint(equalToConstant: 200),
            testView.heightAnchor.constraint(equalToConstant: 200),
        ])

        setupAnimation()

        DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
            self.startAnimation()
        }
    }

    func setupAnimation() {
        scaleAnimator.pausesOnCompletion = true

        scaleAnimator.addAnimations {
            self.testView.transform = CGAffineTransform(scaleX: 1, y: 1e-10) // Scale animations to exactly 0.0 don't work
        }

        scaleAnimator.publisher(for: \.isRunning, options: [.new])
            .sink { [weak self] isRunning in
                guard let self,
                      !isRunning else {
                    print("Animation start")
                    print("Scale Y : \(self!.testView.transform.d)")
                    return
                }

                guard !self.scaleAnimator.isReversed else {
                    print("Animation end")
                    print("Scale Y : \(self.testView.transform.d)")
                    return
                }

                print("Half animation")
                print("Scale Y : \(self.testView.transform.d)")
                self.testView.backgroundColor = .blue
                self.scaleAnimator.isReversed = true
                self.scaleAnimator.startAnimation()
            }
            .store(in: &cancellables)
    }

    func startAnimation() {
        scaleAnimator.isReversed = false
        scaleAnimator.startAnimation()
    }
}

最后，此代码打印 Y 比例为 0，但在屏幕上我有一个 200px 的蓝色方块。如果我检查视图，它的比例是 0.

我在这里做错了什么？