Swift For In Loop 遍历一组自定义类不起作用

Question

我正在做一个项目，在像这样迭代 for in 循环时遇到了这个错误:

class CustomClass {
    
    var nameNum : Int { didSet { self.name = "CustomClass \(nameNum)" } }
    var name : String
    
    init() {
        nameNum = 0
        self.name = "CustomClass \(nameNum)"
    }
}

var myArray : [CustomClass] = [CustomClass](repeating: CustomClass(), count: 5)

for _class in myArray.indices {
    myArray[_class].nameNum = _class
}

print("\n")
for _class in myArray.indices {
    print("Item \(_class): \(myArray[_class].name)")
}

我得到以下输出:

Item 0: CustomClass 4

Item 1: CustomClass 4

Item 2: CustomClass 4

Item 3: CustomClass 4

Item 4: CustomClass 4

这对我来说没有意义，因为我认为我会得到以下输出:

Item 0: CustomClass 0

Item 1: CustomClass 1

Item 2: CustomClass 2

Item 3: CustomClass 3

Item 4: CustomClass 4

对于为什么这不起作用或如何修复它的任何帮助，我们将不胜感激，谢谢!

Answer 1

您应该将数组初始化更改为

var myArray : [CustomClass] = (0..<5).map { _ in CustomClass() }

来自

var myArray : [CustomClass] = [CustomClass](repeating: CustomClass(), count: 5)

完整代码:

class CustomClass {
    
    var nameNum : Int { didSet { self.name = "CustomClass \(nameNum)" } }
    var name : String
    
    init() {
        nameNum = 0
        self.name = "CustomClass \(nameNum)"
    }
}

var myArray : [CustomClass] = (0..<5).map { _ in CustomClass() }

for _class in myArray.indices {
    myArray[_class].nameNum = _class
}

print("\n")
for _class in myArray.indices {
    print("Item \(_class): \(myArray[_class].name)")
}

原因是您的代码实际上创建了一个 CustomClass 实例，并将其添加到数组的所有 5 个索引处，而您期望有 5 个不同的 CustomClass 实例。如果同一个实例被添加 5 次，那么所有实例都将具有最后一个设置值，在您的情况下为 4。

Item 0: CustomClass 0

Item 1: CustomClass 1

Item 2: CustomClass 2

Item 3: CustomClass 3

Item 4: CustomClass 4