将 ObservedObject 传递给嵌套的子视图 SwiftUI(SwiftUI 数据流) [英] Passing An ObservedObject To Nested Child Views SwiftUI (SwiftUI Data Flow)

问题描述

我试图理解为什么传递 @ObservedObject 变量对嵌套的子视图不起作用.可以传递数据，但更改仅反映在创建 @ObservedObject 变量的根视图中.更改不会显示在子视图中.查看 Apple 文档(已针对 Xcode beta 5 进行了更新)，答案似乎是创建一个环境对象和一个常规变量，以便从环境对象中获取正确的索引.这是 Apples 示例.

I'm trying to understand why passing an @ObservedObject variable does not work for nested child views. The data is able to be passed but the changes only reflects at the root view where the @ObservedObject variable was created. The changes don't show in the subviews. Looking at Apple documentation (which has been updated for Xcode beta 5), the answer seems to be to create both an environment object and a regular variable in order to get the correct index from the environment object. Here is Apples example.

我的理解是，@ObservedObject 可用于从多个视图引用变量，但如果您希望数据可从任何视图访问，则应使用环境对象.因此我相信通过@ObservedObject 应该是可能的.我认为正在发生的问题是，由于 ScreenTwo 将 @Binding 变量传递给 DetailsView，这就是导致问题的原因.为了解决这个问题，我认为您需要继续传递完整的@ObservedObject，但是您再次需要某种类型的常规变量来获得正确的索引.

My understanding is that an @ObservedObject can be used to reference a variable from multiple views, but if you want the data to be accessible from any view then you should use an environment object. Therefore I believe that passing the @ObservedObject should be possible. The issue I believe is happening is that since ScreenTwo is passing the @Binding variable to DetailsView and that is what's causing a problem. To solve this I would think you need to keep passing the full @ObservedObject, but then again you would need some type of regular variable to get the proper index.

我觉得所有这些都应该更简单.

I feel like all of this should be much more straightforward.

import SwiftUI
import Combine

struct Sport: Identifiable{
    var id = UUID()
    var name : String
    var isFavorite = false
    var school : String
}

final class SportData: ObservableObject  {
    @Published var store =
        [
            Sport(name: "soccer", isFavorite: false, school: "WPI"),
            Sport(name: "tennis", isFavorite: false, school: "WPI"),
            Sport(name: "swimming", isFavorite: true, school: "WPI"),
            Sport(name: "running", isFavorite: true, school: "RIT"),
    ]
}

struct Testing: View {
    @ObservedObject var sports = SportData()

    var body: some View {
        NavigationView{
            List{
                ForEach($sports.store){ sport in
                    NavigationLink(destination: ScreenTwo(sport: sport)){
                        HStack {
                            Text(sport.value.name)
                            Spacer()
                            Text(sport.value.isFavorite.description)
                        }
                    }
                }
            }
        }.navigationBarTitle("Settings")
    }
}

struct ScreenTwo : View{
    @Binding var sport : Sport

    var body: some View{
        NavigationLink(destination: DetailsView(sport: $sport)){
            Text(sport.isFavorite.description)
        }
    }
}

struct DetailsView: View {
    @Binding var sport : Sport

    var body: some View {
        Button(action: {
            self.sport.isFavorite.toggle()
            self.sport.name = "Ricky"
        }) {
            Text(sport.isFavorite.description)
            Text(sport.name)
        }
    }
}



#if DEBUG
struct Testing_Previews: PreviewProvider {
    static var previews: some View {
        Testing()
    }
}
#endif

推荐答案

对于 ObservableObject 配对 ObservedObject 使视图刷新，因此要解决有问题的任务，我建议以下方法:

For ObservableObject the pairing ObservedObject makes view refresh, so to solve the task in question I would recommend the following approach:

演示

代码

import SwiftUI
import Combine

class Sport: ObservableObject, Hashable, Identifiable {

    static func == (lhs: Sport, rhs: Sport) -> Bool {
        lhs.name == rhs.name && lhs.isFavorite == rhs.isFavorite && lhs.school == rhs.school
    }

    func hash(into hasher: inout Hasher) {
        hasher.combine(name)
        hasher.combine(isFavorite)
        hasher.combine(school)
    }

    @Published var name : String
    @Published var isFavorite = false
    @Published var school : String

    init(name: String, isFavorite: Bool, school: String) {
        self.name = name
        self.isFavorite = isFavorite
        self.school = school
    }
}

final class SportData: ObservableObject  {
    @Published var store =
        [
            Sport(name: "soccer", isFavorite: false, school: "WPI"),
            Sport(name: "tennis", isFavorite: false, school: "WPI"),
            Sport(name: "swimming", isFavorite: true, school: "WPI"),
            Sport(name: "running", isFavorite: true, school: "RIT"),
    ]
}

struct TestingObservedObject: View {
    @ObservedObject var sports = SportData()

    var body: some View {
        NavigationView{
            List{
                ForEach(sports.store){ sport in
                    NavigationLink(destination: ScreenTwo(sport: sport)) {
                        HStack {
                            Text("\(sport.name)")
                            Spacer()
                            Text(sport.isFavorite.description)
                        }
                    }
                    .onReceive(sport.$isFavorite) { _ in self.sports.objectWillChange.send() }
                }
            }
        }.navigationBarTitle("Settings")
    }
}

struct ScreenTwo : View{
    @ObservedObject var sport : Sport

    var body: some View{
        NavigationLink(destination: DetailsView(sport: sport)){
            Text(sport.isFavorite.description)
        }
    }
}

struct DetailsView: View {
    @ObservedObject var sport : Sport

    var body: some View {
        Button(action: {
            self.sport.isFavorite.toggle()
            self.sport.name = "Ricky"
        }) {
            Text(sport.isFavorite.description)
            Text(sport.name)
        }
    }
}



#if DEBUG
struct Testing_Previews: PreviewProvider {
    static var previews: some View {
        TestingObservedObject()
    }
}
#endif

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