我的建议是利用Swift扩展来使代码更加模块化和易于使用。例如，如果你想在多个视图上使多个标签淡入/淡出或一个标签淡入/淡出，你必须到处传递animateWithDuration方法，这可能是一个麻烦。一个更干净的替代方案是创建一个名为UIView.swift的文件（我们的UIView扩展名）。将以下代码添加到此文件：

import Foundation

extension UIView {

func fadeIn(duration: NSTimeInterval = 1.0, delay: NSTimeInterval = 0.0, completion: ((Bool) -> Void) = {(finished: Bool) -> Void in}) {
    UIView.animateWithDuration(duration, delay: delay, options: UIViewAnimationOptions.CurveEaseIn, animations: {
        self.alpha = 1.0
        }, completion: completion)  }

func fadeOut(duration: NSTimeInterval = 1.0, delay: NSTimeInterval = 3.0, completion: (Bool) -> Void = {(finished: Bool) -> Void in}) {
    UIView.animateWithDuration(duration, delay: delay, options: UIViewAnimationOptions.CurveEaseIn, animations: {
        self.alpha = 0.0
        }, completion: completion)
}

}

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现在，您可以将淡入/淡出功能添加到UIView的任何子对象（例如，UILabel，UIImage等）。在viewDidLoad（）函数中，您可以添加：

self.statusLabel.alpha = 0
self.statusLabel.text = "Sample Text Here"
self.myLabel.fadeIn(completion: {
        (finished: Bool) -> Void in
        self.myLabel.fadeOut()
        })

型
现在，你可以将这个示例代码用于图像视图，标签，文本视图，滚动视图，或者UIView的任何子视图。

即使视图已经加载，当调用viewDidLoad时，它可能对用户不可见。这意味着当您见证它时，您可能会发现您的动画似乎已经开始。要克服这个问题，您需要在viewDidAppear中启动动画。
至于fadeIn和fadeOut函数-它们不存在。你需要自己编写它们。谢天谢地，这很容易做到。像下面这样的东西可能就足够了。

func fadeViewInThenOut(view : UIView, delay: NSTimeInterval) {

    let animationDuration = 0.25

    // Fade in the view
    UIView.animateWithDuration(animationDuration, animations: { () -> Void in
        view.alpha = 1
        }) { (Bool) -> Void in

            // After the animation completes, fade out the view after a delay

            UIView.animateWithDuration(animationDuration, delay: delay, options: .CurveEaseInOut, animations: { () -> Void in
                view.alpha = 0
                },
                completion: nil)
    }
}

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Swift 3的答案更新-使用扩展名

extension UIView {
    func fadeIn(duration: TimeInterval = 1.0, delay: TimeInterval = 0.0, completion: @escaping ((Bool) -> Void) = {(finished: Bool) -> Void in}) {
        UIView.animate(withDuration: duration, delay: delay, options: UIViewAnimationOptions.curveEaseIn, animations: {
            self.alpha = 1.0
        }, completion: completion)
    }

    func fadeOut(duration: TimeInterval = 1.0, delay: TimeInterval = 3.0, completion: @escaping (Bool) -> Void = {(finished: Bool) -> Void in}) {
        UIView.animate(withDuration: duration, delay: delay, options: UIViewAnimationOptions.curveEaseIn, animations: {
            self.alpha = 0.0
        }, completion: completion)
    }
}

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用法：

self.statusLabel.alpha = 0
self.statusLabel.text = "Sample Text Here"
self.myLabel.fadeIn(completion: {
        (finished: Bool) -> Void in
        self.myLabel.fadeOut()
        })

型

更新Swift 3.1 -@Andy代码

func fadeViewInThenOut(view : UIView, delay: TimeInterval) {
        let animationDuration = 0.25

        // Fade in the view
        UIView.animate(withDuration: animationDuration, animations: { () -> Void in
            view.alpha = 1
        }) { (Bool) -> Void in

            // After the animation completes, fade out the view after a delay

            UIView.animate(withDuration: animationDuration, delay: delay, options: [.curveEaseOut], animations: { () -> Void in
                view.alpha = 0
            }, completion: nil)
        }
    }

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Swift 4.2

extension UIView {
    func fadeIn(duration: TimeInterval = 1.0, delay: TimeInterval = 0.0, completion: @escaping ((Bool) -> Void) = {(finished: Bool) -> Void in}) {
        UIView.animate(withDuration: duration, delay: delay, options: .curveEaseIn, animations: {
            self.alpha = 1.0
        }, completion: completion)
    }

    func fadeOut(duration: TimeInterval = 1.0, delay: TimeInterval = 3.0, completion: @escaping (Bool) -> Void = {(finished: Bool) -> Void in}) {
        UIView.animate(withDuration: duration, delay: delay, options: .curveEaseIn, animations: {
            self.alpha = 0.0
        }, completion: completion)
    }
}

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• 斯威夫特5号酒店，纽约**

这对我很有效。我把标签放在“cardHeaderView”里面。

@IBOutlet weak var cardHeaderView: UIView!

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把这个放在“viewDidAppear”里面。我把延迟设置为零，这样动画就可以马上开始了。

fadeViewInThenOut(view: cardHeaderView, delay: 0)

型
这是函数。

func fadeViewInThenOut(view : UIView, delay: TimeInterval) {

    let animationDuration = 1.5

    UIView.animate(withDuration: animationDuration, delay: delay, options: [UIView.AnimationOptions.autoreverse, UIView.AnimationOptions.repeat], animations: {
        view.alpha = 0
    }, completion: nil)

}

型