@Published数组中的ObservableObject的更改不会更新视图

Question

我一直在为SwiftUI问题苦苦挣扎数小时。

这是我的问题的简化示例：

class Parent: ObservableObject {
    @Published var children = [Child()]
}

class Child: ObservableObject {
    @Published var name: String?

    func loadName() {
        DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
            // Async task here...
            self.objectWillChange.send()
            self.name = "Loaded name"
        }
    }

}

struct ContentView: View {
    @ObservedObject var parent = Parent()

    var body: some View {
        Text(parent.children.first?.name ?? "null")
            .onTapGesture {
                self.parent.objectWillChange.send()
                self.parent.children.first?.loadName() // does not update
            }
    }
}

我有一个ObservableObject（父级），它存储着@Published的ObservableObjects（子级）数组。

问题在于，当通过对数组中一个对象的异步任务更改name属性时，视图不会更新。

你有什么主意吗？

非常感谢 尼古拉斯

Answer 1

我会说这是设计问题。请在下面找到仅使用SwiftUI功能且不需要任何解决方法的首选方法。关键思想是“视图-视图模型”的分解和显式依赖注入。

通过Xcode 11.4 / iOS 13.4测试

class Parent: ObservableObject {
    @Published var children = [Child()]
}

class Child: ObservableObject {
    @Published var name: String?

    func loadName() {
        DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
            // Async task here...
            self.name = "Loaded name"
        }
    }
}

struct FirstChildView: View {
    @ObservedObject var child: Child
    var body: some View {
        Text(child.name ?? "null")
            .onTapGesture {
                self.child.loadName()
            }
    }
}

struct ParentContentView: View {
    @ObservedObject var parent = Parent()

    var body: some View {
        // just for demo, in real might be conditional or other UI design
        // when no child is yet available
        FirstChildView(child: parent.children.first ?? Child())
    }
}

Answer 2

这种替代方法对我有用：

class Parent: ObservableObject {
@Published var children = [Child()]
}

class Child: ObservableObject {
@Published var name: String?

func loadName(handler: @escaping () -> Void) {
    DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
        // Async task here...
        self.name = UUID().uuidString  // just for testing
        handler()
    }
}
}

struct ContentView8: View {
@ObservedObject var parent = Parent()
var body: some View {
    Text(parent.children.first?.name ?? "null").padding(10).border(Color.black)
        .onTapGesture {
            self.parent.children.first?.loadName(){
                self.parent.objectWillChange.send()
            }
    }
}
} 

Answer 3

确保您的孩子模型是struct！类无法正确更新用户界面。