Question

如果我编写Swift 3代码，它将如下所示：

let animation = CABasicAnimation(keyPath: #keyPath(CAShapeLayer.path))

但是我尝试为keyPath使用Swift 4新语法，我得到了：

let keyPath = \CAShapeLayer.path
let animation = CABasicAnimation(keyPath: keyPath) // error line

＆GT;错误：无法转换类型＆＃39; ReferenceWritableKeyPath＆＃39;的值预期的参数类型＆＃39;字符串？＆＃39;

如何使用swift 4在这种情况下使用密钥路径？

Answer 1

至于现在CABasicAnimation仍使用旧的String keyPaths，因此即使您使用的是Swift 4，仍应使用#keyPath(CAShapeLayer.path)。

Apple将来可能会更新它的所有API，以利用这些更安全的密钥路径引用。但是现在你被“不安全”的字符串困住了。

Answer 2

是的，可以使用快捷键路径。喜欢：

extension UIView {

func animateLayer<Value>(_ keyPath: WritableKeyPath<CALayer, Value>, to value:Value, duration: CFTimeInterval) {

    let keyString = NSExpression(forKeyPath: keyPath).keyPath
    let animation = CABasicAnimation(keyPath: keyString)
    animation.fromValue = self.layer[keyPath: keyPath]
    animation.toValue = value
    animation.duration = duration
    self.layer.add(animation, forKey: animation.keyPath)
    var thelayer = layer
    thelayer[keyPath: keyPath] = value
}
}

用法类似：

animateLayer(\.shadowOffset, to: CGSize(width: 3, height: 3), duration:1)
animateLayer(\.shadowOpacity, to: 0.4, duration: 1)

尚未经过全面测试。但为我工作。

Answer 3

对于Swift 5，您可以使用与此类似的内容：

[
{"name" : "one", "sports" : "cricket", "prize" : "first"},
{"name" : "one", "sports" : "cricket", "prize" : "second"},
{"name" : "one", "sports" : "football", "prize" : "first"},
{"name" : "two", "sports" : "cricket", "prize" : "first"},
{"name" : "two", "sports" : "cricket", "prize" : "second"},
{"name" : "two", "sports" : "football", "prize" : "first"},
{"name" : "three", "sports" : "cricket", "prize" : "second"},    
{"name" : "three", "sports" : "football", "prize" : "first"},    
]

如何在CAShapeLayer动画中使用Swift 4 KeyPath

3 个答案: