[SwiftUI 开发] 嵌套的ObservedObject中的更改不会更新UI

 
1. 发生问题的demo

业务逻辑代码 

class Address: ObservableObject {
    @Published var street = "123 Apple Street"
    @Published var city = "Cupertino"
}

class User: ObservableObject {
    @Published var name = "Tim Cook"
    @Published var address = Address()
}

struct ContentView: View {
    @ObservedObject var user = User()

    var body: some View {
        VStack {
            Text("Name: \(user.name)")
            Text("Address: \(user.address.street), \(user.address.city)")
            Button("Change Address") {
                user.address.street = "New York"
            }
        }
    }
}

当我有一个嵌套的ObservedObject时，嵌套对象的已发布属性的更改不会更新UI，直到父对象发生变化，才会刷新。

 
2.  修改后的代码

SwiftUI(更准确地说是Combine)只能看到值的变化，因此，它可以看到@Published结构实例的属性值的变化，而不能看到@Published类。
如果您希望基于这些嵌套对象的属性值的更改来更新Ul，则使用嵌套对象的结构实例。如果必须使用类实例，请使用另一种机制显式地通知更改。下面是使用struct代替class的NestedObject修改的代码

 业务逻辑代码 

struct Address {
    var street = "123 Apple Street"
    var city = "Cupertino"
}

class User: ObservableObject {
    @Published var name = "Tim Cook"
    @Published var address = Address()
}

struct ContentView: View {
    @ObservedObject var user = User()

    var body: some View {
        VStack {
            Text("Name: \(user.name)")
            Text("Address: \(user.address.street), \(user.address.city)")
            Button("Change Address") {
                user.address.street = "New York"
            }
        }
    }
}

总结一句话，一个对象只需要当前属性@Published就可以了，子类使用struct