如何使标签在swift中淡入或淡出

我希望在viewDidLoad()中使标签淡入，然后在计时器淡出3之后。 我不熟悉fadein或fadeoutfunction。

我该怎么做呢？

Answer 1

即使视图已加载，当调用viewDidLoad时，用户可能看不到该视图。 这意味着当您目击它时，您可能会发现您的动画似乎已经开始。 要解决此问题，您需要在viewDidAppear启动动画。

至于fadeIn和fadeOut函数 – 它们不存在。 你需要自己写。 值得庆幸的是，这很容易做到这一点。 像下面这样的东西可能已经足够了。

 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) } } 

Answer 2

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，如果要在多个视图上制作多个标签fadein / out或一个标签淡入/淡出，则必须在任何地方传递animateWithDuration方法，这可能很麻烦。 更简洁的选择是创建一个名为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) } } 

现在，您可以为任何UIView的子项添加淡入/淡出function（例如，UILabel，UIImage等）。 在viewDidLoad（）函数内部，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() }) 

现在，您可以将此示例代码用于图像视图，标签，文本视图，滚动视图或UIView的任何子项。 我希望这有帮助。

Answer 3

为Swift 3更新了答案 – 使用扩展程序

 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) } } 

用法：

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

Answer 4

更新Swift 3.1 – 关于@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) } }