当我使用属性更新视图时，ObservedObject 会重置。因此会导致数据丢失

Question

我有一个问题，当视图更新时ViewModel 会重新初始化。

我有 2 个视图，SongListView 和 PlayerView，它们共享 Player 的对象。当玩家的 Playing 状态改变(isPlaying == true) 时，SongListView 中的viewModel 重置并变为空数组。因此，我视图上的列表变为空。

歌曲列表视图：

struct SongListView: View {

    @ObservedObject var model: SongListViewModel = SongListViewModel() // This resets when player.isPlaying is set to true

    @ObservedObject var player: Player

    var body: some View {

        List(model.songs, id: \.id) { song in
            Button(action: {
                self.player.play(link: song.link)
            }) {
                TitleRowView(title: song)
            }
        }
        .onAppear {
            self.model.get()
        }
        .navigationBarTitle(Text("Songs"), displayMode: .inline)
    }
}

SongListViewModel：

class SongListViewModel: ObservableObject {

    @Published var songs: [Song] = [Song(id: 2, name: "ish", link: "ishm")] // When I tap the row, the songs var is re-initialized

    func get() {

        guard let url = URL(string: "apiPath") else { return }

        URLSession(configuration: URLSessionConfiguration.default).dataTask(with: url) {data, response, error 
               // Some more code
               self.songs = data
        }.resume()
    }
}

播放器视图：

struct PlayerView: View {

    @ObservedObject var player: Player

    var body: some View {
        HStack {
            Button(action: {
                if self.player.isPlaying {
                    self.player.pause()
                } else {
                    self.player.play()
                }
            }) {
                // This change causes the viewModel to reset to empty array
                if self.player.isPlaying { 
                    Image(systemName: "pause.fill")
                        .resizable()
                } else {
                    Image(systemName: "play.fill")
                        .resizable()
                }
            }
        }
    }
}

玩家：

class Player : ObservableObject
{

    @Published var isPlaying: Bool = false

    private var player: AVPlayer?

    // This method is called when the user taps on a row in List
    func play(link: String) {
        guard let url = URL(string: link) else { return }
        let playerItem = AVPlayerItem(url: url)
        player = AVPlayer(playerItem: playerItem)
        player?.play()
        isPlaying = true // If I comment this line, the songs list in viewModel does not changes
    }    
}

提前致谢！

更新：仍然不起作用

struct SongListView: View {

    @ObservedObject var model: SongListViewModel

    var body: some View {
        // View 
    }
}

struct CategoryListView: View {
    var categoryData : [Category]
    @ObservedObject var player: Player

    var body: some View {
        List(categoryData, id: \.id) { category in
            if category.id == 3 {
                NavigationLink(destination: SongListView(model: SongListViewModel(), player: self.player)) {
                    TitleRowView(title: category)
                }
            }

        }
    }
}

Answer 1

SwiftUI 视图是结构体，因此是不可变的。当您更新状态并导致视图重绘时，它实际上会创建一个新的视图实例。

在您的SongListView 中有

@ObservedObject var model: SongListViewModel = SongListViewModel()

这意味着每次重新绘制 SongListView 时（包括更改 player.isPlaying 的任何时间），您将使用 SongListViewModel 的新实例初始化 model。

您应该删除默认值并通过参数将模型提供给SongListView的初始化器-

@ObservedObject var model: SongListViewModel

Answer 2

使用 @StateObject 而不是 @ObservedObject 对我有用。

只要需要视图，标记为 @StateObject 的属性将保留其最初分配的 ObservedObject 实例，即使结构被 SwiftUI 重新创建。

这允许您维护 ObservedObject 数据的状态。

Answer 3

改用@StateObject！ ObservedObject 似乎每次都在重新创建整个对象。

Answer 4

所以最后我能够通过删除player: Player 上的@ObservedObject 属性包装器来解决这个问题。我不确定为什么会这样。似乎在一个视图中有多个 ObservedObject 会导致此问题。现在我的代码如下所示：

struct SongListView: View {

    @ObservedObject var model: SongListViewModel

    @State var player: Player

    var body: some View {

        List(model.songs, id: \.id) { song in
            Button(action: {
                self.player.play(link: song.link)
            }) {
                TitleRowView(title: song)
            }
        }
        .onAppear {
            self.model.get()
        }
        .navigationBarTitle(Text("Songs"), displayMode: .inline)
    }
}

struct CategoryListView: View {
    var categoryData : [Category]
    @ObservedObject var player: Player
    let viewModel = SongListViewModel()

    var body: some View {
        List(categoryData, id: \.id) { category in

            if category.id == 3 {
                NavigationLink(destination: SongListView(player: self.player).environmentObject(self.viewModel)) {
                    TitleRowView(title: category)
                }
            }

        }
    }
}