swift - SwiftUI View 协议(protocol)中的 EnvironmentObject

Question

我想制定这样的协议(protocol):

protocol SubscriptionManagerView: View {
    var subscriptionManager: EnvironmentObject<SubscriptionManager> { get set }
}

以这样的 View 为例:

struct Shop: View, SubscriptionManager {
    @EnvironmentObject var subscriptionManager: SubscriptionManager

第一个问题是属性包装器@EnvironmentObject 不能让我响应协议(protocol) SubscriptionManagerView。
最后我想使用这样的自定义修饰符:

extension View where Self : SubscriptionManagerView {
    func subscriptionManagerAlert() -> some View {
        self.alert(isPresented: self.$subscriptionManager.stateShowAlert) {
            Alert(title: Text(self.subscriptionManager.transactionStateTitle)
                ...
                  }))
        }
    }
}

任何想法以这种方式工作？

Answer 1

这是一个可能的方法的演示 - 想法是使用 View 修饰符和显式注入(inject)的订阅管理器，因此接口(interface)契约保证修饰符的客户端 View 将为我们提供所需的对象。
使用 Xcode 12/iOS 14 测试。

class SubscriptionManager: ObservableObject {
    @Published var stateShowAlert: Bool = false
    @Published var transactionStateTitle = "Test"
}

struct SubscriptionManagerModifier: ViewModifier {
    @ObservedObject var subscriptionManager: SubscriptionManager
    func body(content: Content) -> some View {
        content
            .alert(isPresented: self.$subscriptionManager.stateShowAlert) {
                Alert(title: Text(self.subscriptionManager.transactionStateTitle))
            }
    }
}

extension View {
    func subscriptionManagerAlert(with subscriptionManager: SubscriptionManager) -> some View {
        self.modifier(SubscriptionManagerModifier(subscriptionManager: subscriptionManager))
    }
}

struct Shop: View {
    
    @EnvironmentObject var subscriptionManager: SubscriptionManager
    
    var body: some View {
        Button("Test") {
            subscriptionManager.stateShowAlert.toggle()
        }
        .subscriptionManagerAlert(with: subscriptionManager)
    }
}

struct Shop_Previews: PreviewProvider {
    static var previews: some View {
        Shop().environmentObject(SubscriptionManager())
    }
}