ios - 许多不同字符串之间的 Swift UIView.animate

Question

我希望在从新设备启动后重新创建 iPhone 上出现的欢迎屏幕上的动画 - 您在这里看到的各种不同语言的问候语 - https://www.youtube.com/watch?v=YZDbGyvAK7o

我的问题是我有大约 20 多个字符串我想在它们之间淡入/淡出，但我不相信创建 20 多个不同的 UILabel 是解决这个问题的最有效方法。必须有另一种方法来执行此操作，而不是对其进行硬编码。

这是到目前为止我对关键帧的了解

//textC UIlabel declaration and initialising its' properties.   
UIView.animateKeyframes(withDuration: total, delay: 0, options: [.calculationModeLinear, .repeat], animations: {

    UIView.addKeyframe(withRelativeStartTime: 0, relativeDuration: 1/total, animations: {
                let attributedStrD = NSMutableAttributedString(string: countryArr[0], attributes: resultAttributes as [NSAttributedStringKey : Any])
                print(attributedStrD.string)
                textC.attributedText = attributedStrD

            })

    UIView.addKeyframe(withRelativeStartTime: 1/total, relativeDuration: 1/total, animations: {
                let attributedStrD = NSMutableAttributedString(string: countryArr[0], attributes: resultAttributes as [NSAttributedStringKey : Any])
                textC.alpha = 0
                textC.attributedText = attributedStrD

            })
    UIView.addKeyframe(withRelativeStartTime: 2/total, relativeDuration: 1/total, animations: {
                textC.alpha = 1
                let attributedStrD = NSMutableAttributedString(string: countryArr[1], attributes: resultAttributes as [NSAttributedStringKey : Any])
                textC.attributedText = attributedStrD
                print("2")
            })
    UIView.addKeyframe(withRelativeStartTime: 3/total, relativeDuration: 1/total, animations: {
                textC.alpha = 0

                let attributedStrD = NSMutableAttributedString(string: countryArr[1], attributes: resultAttributes as [NSAttributedStringKey : Any])
                textC.attributedText = attributedStrD
            })

    UIView.addKeyframe(withRelativeStartTime: 4/total, relativeDuration: 1/total, animations: {
                textC.alpha = 1

                let attributedStrD = NSMutableAttributedString(string: countryArr[2], attributes: resultAttributes as [NSAttributedStringKey : Any])
                textC.attributedText = attributedStrD
            })

    UIView.addKeyframe(withRelativeStartTime: 5/total, relativeDuration: 1/total, animations: {
                textC.alpha = 0

                let attributedStrD = NSMutableAttributedString(string: countryArr[2], attributes: resultAttributes as [NSAttributedStringKey : Any])
        textC.attributedText = attributedStrD
            })
        }) { (_) in
             print("done animation")
        }

这也不太有效，因为文本没有更新，而是在模拟器上构建和运行时看到数组中的最后一个字符串。

更新: 虽然我想避免使用计时器，但这似乎是唯一适合我的方法。所以我做了一个 UIView 扩展，它使用 CATransitionView 淡化标签，你可以在 stackoverflow 上找到它的一个例子。然后我创建了一个计时器，它将运行淡入淡出动画并使用一个标签循环遍历字符串

Answer 1

您可以使用 UIView.transition 在单个 UILabel 中交叉淡入淡出文本，使用 Timer 启动下一个动画:

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.

    self.textLabel.text = self.strings[stringIndex]

    let _ = Timer.scheduledTimer(withTimeInterval: 3.0, repeats: true) { (timer) in
        self.stringIndex = (self.stringIndex + 1) % self.strings.count

        UIView.transition(with: self.textLabel, duration: 0.8, options: .transitionCrossDissolve, animations: {
            self.textLabel.text = ""
        }, completion: { (Void) in
            UIView.transition(with: self.textLabel, duration: 0.8, options: .transitionCrossDissolve, animations: {
                self.textLabel.text = self.strings[self.stringIndex]
            }, completion: nil)
        })

    }
}