无法将Binding<Type>转换为Binding<Protocol>

Question

Cannot convert Binding<Type> to Binding<Protocol>是特定的错误消息，但潜在的问题是:什么是保存引用、然后从底层对象进行变异和读取的好架构？

示例：

• 在RPG中，你的角色有一个currentArmor。你想要它受到伤害。
• 在口袋妖怪，你跟踪一个currentPokemon。它需要升级。Instagram中的
• ，您有一个selectedPost，您希望使用like按钮来改变底层的post。

。

下面是我尝试过的一个具体例子:这个应用程序有几个Animal，您可以使用这个应用程序来编辑currentAnimal的name。

错误 Cannot assign value of type 'Binding<Dog>' to type 'Binding<Animal>'

protocol Animal {
    var name: String { get set }
}

struct Cow: Animal {
    var name: String
}

struct Dog: Animal {
    var name: String
}

class Model: ObservableObject {
    @Published var dog: Dog = Dog(name: "dog 1")
    // ** THIS IS THE IMPORTANT PART ** //
    @Published var currentAnimal: Binding<Animal> = .constant(Cow(name: "cow 1"))
}

struct ContentView: View {
    @StateObject var model = Model()
    
    var body: some View {
        VStack {
            Text(model.dog.name) // Show the underlying Dog
        }
            .onAppear {
                model.currentAnimal = $model.dog // Cannot assign value of type 'Binding<Dog>' to type 'Binding<Animal>'
            }
            .onTapGesture {
                model.currentAnimal.wrappedValue.name = "dog 2" // Mutate state here
            }
    }
}

是的，我知道https://developer.apple.com/forums/thread/652064，但我不认为做一个强制as!的案子是个好主意。有什么方法可以用泛型代替协议来解决这个问题吗？或者是类继承而不是协议？还是其他建筑？

Answer 1

编辑:它与类一起工作：

protocol Animal {
    var name: String { get set }
}

class Cow: Animal {
    var name: String
    
    init(name: String) {
        self.name = name
    }
}

class Dog: Animal {
    var name: String
    
    init(name: String) {
        self.name = name
    }
}

class Model: ObservableObject {
    @Published var dog: Dog = Dog(name: "dog 1")
    // ** THIS IS THE IMPORTANT PART ** //
    @Published var currentAnimal: Animal = Cow(name: "cow 1")
}

struct ContentView: View {
    @StateObject var model = Model()
    
    var body: some View {
        VStack {
            Text(model.dog.name) // Show the underlying Dog
        }
        .onAppear {
            model.currentAnimal = model.dog // Cannot assign value of type 'Binding<Dog>' to type 'Binding<Animal>'
        }
        .onTapGesture {
            model.currentAnimal.name = "dog 2" // Mutate state here
        }
    }
}