Swift 符合协议子类

Question

在我的应用程序中，我有多个依赖于模型的 UIView 子类。每个采用'Restorable'协议的类都包含模型的超类。每个子模型都描述了特定的 UIView 不常见属性。

// Super-model
public protocol StoryItem {
    var id: Int64? { get }
}

// Parent protocol
public protocol Restorable: AnyObject {
    var storyItem: StoryItem? { get set }
}

// Specific protocol
public struct TextItem: StoryItem {
    public var id: Int64?
    public var text: String?
}

// Not complling
class ResizableLabel: UILabel, Restorable {
    var storyItem: TextItem?
}

我收到以下编译器错误：

*Type 'ResizableLabel' does not conform to protocol 'Restorable'*

我可以让它编译的唯一方法是将ResizableLabel更改为

// Works
class ResizableLabel: UILabel, Restorable {
    var storyItem: StoryItem?
}

有什么方法可以符合协议子类吗？它会使 Init 过程更加干净。感谢您的帮助！

Answer 1

改变

public protocol Restorable: AnyObject {
    var storyItem: StoryItem? { get set } // adopter must declare as StoryItem
}

到

public protocol Restorable: AnyObject {
    associatedtype T : StoryItem
    var storyItem: T? { get set } // adopter must declare as StoryItem adopter
}

现在您的代码可以编译了。完整示例：

public protocol StoryItem {
    var id: Int64? { get }
}
public protocol Restorable: AnyObject {
    associatedtype T : StoryItem
    var storyItem: T? { get set }
}
public struct TextItem: StoryItem {
    public var id: Int64?
    public var text: String?
}
class ResizableLabel: UILabel, Restorable {
    var storyItem: TextItem? // ok because TextItem is a StoryItem adopter
}