swiftUI：更新視圖

我無法弄清楚為什么視圖沒有更新，請幫忙。在實際專案中，我通過 websocket 獲取資料（并使用 設定變數DispatchQueue.main.async {}）。下面以代碼為例。單擊按鈕后，視圖沒有任何反應。我使用 ObservableObject，Published 屬性。有什么問題？

附言。它需要在帖子中添加更多文本，因為它主要是代碼，但我不知道要添加什么，一切都在下面:)

import SwiftUI

class DataBase: ObservableObject {
    
    @Published var data: [MyData]
    @Published var users: [User]
    
    init(data: [MyData], users: [User]) {
        self.data = data
        self.users = users
    }
}

class MyData: ObservableObject, Identifiable {
    
    @Published var type: String
    @Published var array: [Double]
    
    init(type: String, array: [Double]) {
        self.type = type
        self.array = array
    }
}

class User: ObservableObject, Identifiable {
    
    @Published var id: UUID = UUID()
    @Published var name: String
    @Published var data: MyData
    
    init(name: String, data: MyData) {
        self.name = name
        self.data = data
    }
}

let data: [MyData] = [
    MyData(type: "type1", array: [1, 2, 3]),
    MyData(type: "type2", array: [4, 5, 6, 7]),
]

let users: [User] = [
    User(name: "Tim", data: data[0]),
    User(name: "Steve", data: data[1]),
]

struct ContentView: View {
    
    let db = DataBase(data: data, users: users)
    
    var body: some View {
        ShowView(db: db)
    }
}

struct ShowView: View {
    
    @ObservedObject var db: DataBase
    
    var body: some View {
        
        HStack {
            
            List(db.users) { user in
                Text("\(user.name) \(user.data.type)")
                Text("\(user.data.array.count)")
                Divider()
            }
            
            List(db.data) { data in
                Text("\(data.type)")
                Text("\(data.array.count)")
                Divider()
            }
        }
        
        HStack {
            Button("add data to data[0]") {
                db.data[0].array.append(db.data[0].array.last!   10)
                print(db.data[0].array)
            }
            
            Button("add data to data[1]") {
                db.data[1].array.append(db.data[1].array.last!   20)
                print(db.data[1].array)
            }
        }
        
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

uj5u.com熱心網友回復：

試試這個objectWillChange，對我有用：

struct ShowView: View {
    
    @ObservedObject var db: DataBase
    
    var body: some View {
        
        HStack {
            
            List(db.users) { user in
                Text("\(user.name) \(user.data.type)")
                Text("\(user.data.array.count)")
                Divider()
            }
            
            List(db.data) { data in
                Text("\(data.type)")
                Text("\(data.array.count)")
                Divider()
            }
        }
        
        HStack {
            Button("add data to data[0]") {
                db.objectWillChange.send()  // <-- here
                db.data[0].array.append(db.data[0].array.last!   10)
                print(db.data[0].array)
            }
            
            Button("add data to data[1]") {
                db.objectWillChange.send()  // <-- here
                db.data[1].array.append(db.data[1].array.last!   20)
                print(db.data[1].array)
            }
        }
        
    }
}

uj5u.com熱心網友回復：

只需將模型作為值型別（即struct代替class） - 無需更多更改：

struct MyData: Identifiable {
    var id = UUID()
    var type: String
    var array: [Double]

    init(type: String, array: [Double]) {
        self.type = type
        self.array = array
    }
}

struct User: Identifiable {

    var id: UUID = UUID()
    var name: String
    var data: MyData

    init(name: String, data: MyData) {
        self.name = name
        self.data = data
    }
}

使用 Xcode 13.4 / iOS 15.5 測驗

更新

然后需要ObservedObject為每個可觀察的模型物件創建分離的視圖，比如

List(db.users) {
   UserRowView(user: $0)
}

struct UserRowView: View {
  @ObservedObject var user: User  // a class, so needed to be observed

  var body: some View {
    Text("\(user.name) \(user.data.type)")
    Text("\(user.data.array.count)")
    Divider()
  }
}

相同MyData，或進行依賴更新，例如

class User: ObservableObject {
    @Published var data: MyData

    // ...

    private var cancellable: AnyCancellable?
    init(...) {
        // ....
        cancellable = data.objectWillChange.sink { [weak self] _ in
            guard let self = self else { return }
            self.objectWillChange.send()
        }
    }
}

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