Swift 符合协议子类

Question

在我的应用程序中，我有多个依赖模型的 UIView 子类。类中的每一个都采用“Restorable”协议来保存模型的超类。每个子模型描述了特定的 UIView 不常用属性。

// 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？它将使 Init 进程更清洁。感谢您的帮助！

Answer 1

改变

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

至

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
}

Swift 符合协议子类

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