Question

根据＆＃34; Swift编程语言2.1＆＃34;，如果子类为其所有属性提供默认值，则子类自动继承其所有超类的指定初始化器和便利初始化器。因此，对于下面的代码，类ShoppingListItem应该从其超类RecipeIngredient继承三个初始化器，即

//1
convenience init() {
    self.init(name: "[unnamed]")
}

//2
convenience init(name: String){
    self.init(name: name, quantity: 1)
}

//3
init(name: String, quantity: Int){
    self.quantity = quantity
    super.init(name: name)
}

如果我想创建ShoppingListItem的实例，我会写

let ingredientThree = ShoppingListItem(name: "apple", quantity: 10)

这会调用init(name: String, quantity: Int){}，但在此初始化程序中，会调用super.init(name: name)，这就是我被卡住的地方。初始化过程达到super.init(name: name)时会发生什么？它是否会调用ShoppingListItem的超类init(name: String){}初始化程序？或者不是吗？究竟发生了什么？请有人请向我解释一下吗？在此先感谢您的帮助！

实际代码：

class Food {
    var name: String
    init(name: String){
        self.name = name
    }
    convenience init() {
        self.init(name: "[unnamed]")
    }

}

class RecipeIngredient: Food{
    var quantity: Int
    init(name: String, quantity: Int){
        self.quantity = quantity
        super.init(name: name)
    }

    override convenience init(name: String){
        self.init(name: name, quantity: 1)
    }
}

class ShoppingListItem: RecipeIngredient {
    var purchased = false
    var description: String {
        var output = "\(quantity) X \(name)"
        output += purchased ? " ✔" : " ✘"
        return output
    }
}

Swift编程语言的图2.1

Answer 1

我将您的代码放入游乐场并添加了一些打印件。以下是发生的事情：

RecipeIngredient.init（String，Int）
Food.init

顺便提一下，你问过它是否会调用ShoppingListItem的超类的init（name：String）{}初始值。

答案是否定的。你用过的

let ingredientThree = RecipeIngredient(name: "apple", quantity: 10)

这与ShoppingListItem无关。

通常，如果您具有类继承Class1＆lt; - Class2＆lt; - Class3。然后你实例化Class2，然后Class 3永远不会发挥作用。

class Food {
    var name: String
    init(name: String){
        print("Food.init")
        self.name = name
    }
    convenience init() {
        self.init(name: "[unnamed]")
    }

}

class RecipeIngredient: Food{
    var quantity: Int
    init(name: String, quantity: Int){
        print("RecipeIngredient.init(String, Int)")
        self.quantity = quantity
        super.init(name: name)
    }

    override convenience init(name: String){
        self.init(name: name, quantity: 1)
    }
}

class ShoppingListItem: RecipeIngredient {
    var purchased = false
    var description: String {
        var output = "\(quantity) X \(name)"
        output += purchased ? " ✔" : " ✘"
        return output
    }
}
let ingredientThree = RecipeIngredient(name: "apple", quantity: 10)

在swift初始化时的困惑

1 个答案: