Question

我试图让一个非常基本的CAGradientLayer动画工作。我有一个基本的2色CAGradientLayer设置并添加到我的UIViewController。

// Set up the gradient layer.
var gradientLayer: CAGradientLayer! {
    let layer = CAGradientLayer()
    layer.frame = self.view.bounds
    layer.colors = [UIColor.redColor().CGColor, UIColor.yellowColor().CGColor]
    layer.locations = [0.0, 1.0]
    return layer
}

我正在尝试使用以下代码为其设置动画：

@IBAction func changeBackground(sender: AnyObject) {
    let oldColors = self.gradientLayer.colors
    let newColors = [UIColor.purpleColor().CGColor, UIColor.blueColor().CGColor]
    self.gradientLayer.colors = newColors
    let animation: CABasicAnimation = CABasicAnimation(keyPath: "colors")

    animation.fromValue = oldColors
    animation.toValue = newColors
    animation.duration = 0.3
    animation.removedOnCompletion = true
    animation.fillMode = kCAFillModeForwards
    animation.timingFunction = CAMediaTimingFunction(name: kCAMediaTimingFunctionLinear)
    animation.delegate = self

    self.gradientLayer.addAnimation(animation, forKey: "animateGradientColorChange")
}

但是，此代码不会对CAGradientLayer产生任何变化。我在这里做错了什么？

Answer 1

每次从layer属性返回一个新的gradientLayer对象。你需要稍微改变它，以便懒惰地启动它：

lazy var gradientLayer: CAGradientLayer! = {
    let layer = CAGradientLayer()
    layer.frame = self.view.bounds
    layer.colors = [UIColor.redColor().CGColor, UIColor.yellowColor().CGColor]
    layer.locations = [0.0, 1.0]
    return layer
}()

为了完整起见，你原来的是一个计算属性，这意味着每次访问它时都会执行代码。使用延迟属性时，代码只在首次访问属性时执行一次，然后返回相同的对象。

这个游乐场可以观察到差异：

//: Playground - noun: a place where people can play

import UIKit

struct Dummy {

    var gradientLayer: CAGradientLayer! {
        let layer = CAGradientLayer()
        layer.colors = [UIColor.redColor().CGColor, UIColor.yellowColor().CGColor]
        layer.locations = [0.0, 1.0]
        return layer
    }

    lazy var lazyGradientLayer: CAGradientLayer! = {
        let layer = CAGradientLayer()
        layer.colors = [UIColor.redColor().CGColor, UIColor.yellowColor().CGColor]
        layer.locations = [0.0, 1.0]
        return layer
    }()
}

var dummy = Dummy()

let l1 = dummy.gradientLayer
let l2 = dummy.gradientLayer

let lazy1 = dummy.lazyGradientLayer
let lazy2 = dummy.lazyGradientLayer

CAGradientLayer颜色更改动画未执行

1 个答案: