Swift 4中的Smart KeyPaths无法正常工作 [英] Smart KeyPaths in Swift 4 not working properly

问题描述

我正在尝试为SKSpriteNode创建自定义操作块，我有以下代码:

I am trying to create an custom action block for an SKSpriteNode, I have the following code:

let sprite = SKSpriteNode(color: SKColor.red, size: CGSize(width: 50, height: 50))
sprite.position = CGPoint(x: 320, y: 240)    
self.addChild(sprite)

let animation = SKAction.customAction(withDuration: 0, actionBlock: {
    (node, elapsedTime) in

    var initialValue : CGFloat?
    initialValue = node[keyPath: \SKSpriteNode.position.x] //Extraneous argument label 'keyPath:' in subscript

    node[keyPath: \SKSpriteNode.position.x] = 10 //Ambiguous reference to member 'subscript'
})

sprite.run(animation)

我遇到两个错误，第一个是编译器以为我有一个'keyPath'的无关参数，事实并非如此，因为如果我按照建议的方式删除它，则会出现此错误:

I am getting two errors, the first is that the compiler is thinking I have an Extraneous argument of 'keyPath', which is not the case, because if I were to remove it like it suggests, I get this error:

无法将类型"ReferenceWritableKeyPath"的值转换为预期的参数类型字符串"

Cannot convert value of type 'ReferenceWritableKeyPath' to expected argument type 'String'

我得到的第二个错误是:

The second error I get is:

对成员下标"的含糊不清

Ambiguous reference to member 'subscript'

我不确定为什么会收到所有这些错误，也不确定这些错误意味着什么.如果有人可以向我解释它们并提出解决方案，那就太好了.预先感谢.

I am not exactly sure why I am getting all of these errors, and I am not sure exactly what the errors mean. If somebody could explain them to me and propose a solution, that would be great. Thanks in advance.

推荐答案

keyPath不起作用，因为node具有类型SKNode而不是SKSpriteNode.您可以使用条件转换来确定该节点是SKSpriteNode:

The keyPath isn't working because node has type SKNode and not SKSpriteNode. You can use a conditional cast to establish that the node is an SKSpriteNode:

let animation = SKAction.customAction(withDuration: 0, actionBlock: {
    (node, elapsedTime) in

    var initialValue : CGFloat?
    if let spritenode = node as? SKSpriteNode {
        initialValue = spritenode[keyPath: \SKSpriteNode.position.x]

        spritenode[keyPath: \SKSpriteNode.position.x] = 10
    }
})

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