swift - 使用更少的参数在 Swift 中方便地初始化

Question

我正在尝试执行以下代码，但出现编译错误。我想在没有参数的情况下进行初始化，因为所有参数都设置为默认值，但我仍然需要使用父类(super class)的指定初始化程序。我希望能够为新的 AimNode 调用 AimNode()

class AimNode: SKSpriteNode {

    override init() {
        super.init(imageNamed: "aim")
    }

    required init(coder aDecoder: NSCoder) {

    }
}

Answer 1

您的子类 (AimNode) 需要调用您的父类(super class) (SKSpriteNode) 的指定初始化程序。规则，如 Initializer Chaining 中所述快速编程指南的部分是:

To simplify the relationships between designated and convenience initializers, Swift applies the following three rules for delegation calls between initializers:

Rule 1 A designated initializer must call a designated initializer from its immediate superclass.

Rule 2 A convenience initializer must call another initializer from the same class.

Rule 3 A convenience initializer must ultimately call a designated initializer.

SKSpriteNode 的适当指定初始化程序是:

init(texture: SKTexture!, color: UIColor!, size: CGSize)

因此，您需要创建一个 SKTexture，选择颜色并设置大小。幸运的是，这相当简单:

class AimNode: SKSpriteNode {

    // NOTE: I arbitrarily picked white for the color. I believe that's the default, but I don't know for sure.
    override init() {
        let texture = SKTexture(imageNamed: "aim")
        super.init(texture: texture, color: UIColor.whiteColor(), size: texture.size())
    }

    // NOTE: You'll have to implement this too, if you don't have anything custom, you can just call the super implementation
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }
}