ListView not updating after item class is modified in swiftui

Question

I have a list view of Task items. Every 10 seconds a timer triggers the function randomTasks that is responsible to modify the title and the description of each tasks in the list but the ListView doesn’t reflect the changes.I tried to use objectWillChange.send() but it doesn’t work.

I’ve noticed that when a task is modified with a different id the ListView updates and I can see the changes but when i’m in the detail view whenever randomTaskTitle is triggered the view is dismissed automatically.

class Task {
    var id: String = UUID().uuidString
    var title: String
    var description: String

    init(title: String, description: String) {
        self.title = title
        self.description = description
    }
}


import SwiftUI

struct TasksView: View {
    
    @EnvironmentObject var viewModel: TasksViewModel

        let timer = Timer.publish(every: 10, on: .main, in: .common).autoconnect()
    
    var body: some View {
        
        NavigationView {
          List {
            ForEach(viewModel.tasks, id: \.id) { task in          
               NavigationLink(
                  destination: DetailView(task: task)
               ) {
                  VStack {
                    Text(task.title)
                    Text(task.description)
                  }
               }
          }
        }
        .onReceive(timer) { time in
            Task {
                await viewModel.randomTasks()
            }
        }
        
    }
}

struct TasksViewNew_Previews: PreviewProvider {
    static var previews: some View {
        TasksView()
    }
}

import Foundation

@MainActor
class TasksViewModel: ObservableObject {

    @Published var tasks = [Task]()

    init() {
      self.tasks = [Task(title: "TaskA", description: "DescriptionA"),
                    Task(title: "TaskB", description: "DescriptionB"),
                    Task(title: "TaskC", description: "DescriptionC"),
                    Task(title: "TaskD", description: "DescriptionD"),]
    }
    
    func randomTasks() {
      tasks.forEach { task in
        task.title = randomTitleTask()
        task.description = randomDescriptionTask()
      }
    }
    
}

Does this answer your question? Why an ObservedObject array is not updated in my SwiftUI application? — Phil Dukhov
– Phil Dukhov, Commented Sep 6, 2021 at 10:12

workingdog support Ukraine · Accepted Answer · 2021-09-06 12:27:53Z

2

try something simple like this, that works well for me:

@MainActor
class TasksViewModel: ObservableObject {
    
    @Published var tasks = [Task]()
    
    init() {
        self.tasks = [Task(title: "TaskA", description: "DescriptionA"),
                      Task(title: "TaskB", description: "DescriptionB"),
                      Task(title: "TaskC", description: "DescriptionC"),
                      Task(title: "TaskD", description: "DescriptionD"),]
    }
    
    func randomTasks() {
        tasks.forEach { task in
            task.title = randomTitleTask()
            task.description = randomDescriptionTask()
        }
        objectWillChange.send()   // <--- here
    }
}

struct TasksView: View {
    @EnvironmentObject var viewModel: TasksViewModel
    let timer = Timer.publish(every: 10, on: .main, in: .common).autoconnect()
    
    var body: some View {
        NavigationView {
            List {
                ForEach(viewModel.tasks, id: \.id) { task in
                    NavigationLink(destination: DetailView(task: task)) {
                        VStack {
                            Text(task.title)
                            Text(task.description)
                        }
                    }
                }
            }
            .onReceive(timer) { time in
                // no need for Task here since randomTasks is not an async
                viewModel.randomTasks()  // <--- here
            }
        }
    }
}

edited Sep 6, 2021 at 12:27

answered Sep 6, 2021 at 10:10

workingdog support Ukraine

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2 Comments

George Over a year ago

I believe you should have objectWillChange.send() before tasks.forEach ...

workingdog support Ukraine Over a year ago

yeah, you could put it before. In my basic tests, it seems to work just as well after.

Phil Dukhov · Accepted Answer · 2021-09-07 03:52:13Z

1

The @Published array from classes does not know when your objects have changed. It can only keep track of when you add/remove them.

You can tell your ObservableObject that something has changed explicitly by calling objectWillChange.send() before your modifications

objectWillChange.send()
tasks.forEach { task in
    task.title = UUID().uuidString
    task.description = UUID().uuidString
}

Convert your class into a struct, and change items by index, like

tasks.indices { i in
    tasks[i].title = UUID().uuidString
    tasks[i].description = UUID().uuidString
}

Check out ObservableArray from this answer

edited Sep 7, 2021 at 3:52

answered Sep 6, 2021 at 10:16

Phil Dukhov

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Comments

keyvan yaghoubian · Accepted Answer · 2021-09-07 00:05:16Z

0

Instead of @ObservedObject use @StateObject

answered Sep 7, 2021 at 0:05

keyvan yaghoubian

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