Question

extension UIView {

    func startBlinking() {
        UIView.animate(withDuration: 0.8, delay: 0.0, options: [.allowUserInteraction, .curveEaseInOut, .autoreverse, .repeat], animations: { self.alpha = 0 }, completion: nil)
    }
}

我如何使用它？

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    monthLabel.startBlinking()
}

第一次调用method时，它闪烁...但是第二次出现视图时，标签消失，而仅此而已。

为什么它不再起作用？

我的日志：

did load
did appear
start blinking
did appear
start blinking

Answer 1

尝试：

import UIKit

protocol Then {}

extension Then {
    func then(_ block: (Self) -> Void) -> Self {
        block(self)
        return self
    }
}

extension UIView: Then {}

class ViewController: UIViewController {

    private var animate: ((Bool) -> Void)?
    private var canAnimate: Bool = true

    override func viewDidLoad() {
        super.viewDidLoad()

        let label = UILabel().then {
            $0.text = "Hello World!"
            $0.textColor = .black
            $0.translatesAutoresizingMaskIntoConstraints = false
        }

        view.addSubview(label)
        NSLayoutConstraint.activate([
            label.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            label.centerYAnchor.constraint(equalTo: view.centerYAnchor)
        ])

        animate = { [weak self] (forward) in
            UIViewPropertyAnimator.runningPropertyAnimator(withDuration: 1.0, delay: 0.0, options: [.curveLinear, .autoreverse, .repeat], animations: {

                label.alpha = forward ? 0.0 : 1.0

            }, completion: { [weak self] _ in
                if self?.canAnimate ?? true {
                    DispatchQueue.main.asyncAfter(deadline: .now() + 0.25, execute: {
                        self?.animate?(!forward)
                    })
                }
            }).startAnimation()
        }

        animate?(true)

     DispatchQueue.main.asyncAfter(deadline: .now() + 2.0) {
            let controller = UIViewController()
            self.navigationController?.pushViewController(controller, animated: true)
        }
    }

    override func viewDidDisappear(_ animated: Bool) {
        super.viewDidDisappear(animated)

        canAnimate = false
    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        canAnimate = true
        animate?(true)
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }


}

Answer 2

您需要重新启动alpha

func startBlinking() {
    self.layer.removeAllAnimations() 
    self.alpha = 1.0
    UIView.animate(withDuration: 0.8, delay: 0.0, options: [.allowUserInteraction, .curveEaseInOut], animations: { self.alpha = 0.0 }, completion: nil)
}

当视图再次出现时，动画停止工作

2 个答案: