Swift Combine Not Receiving Published Values - swift

Question

I am working on a project that is using Combine to get updates from Firebase Firestore. I have a StockListView, a StockListCellView, and a StockDetailView that I want updates to be registered in.
The StockListView holds StockListCellViews which push StockDetailsViews onto the stack. Each view also has a corresponding ViewModel where I am working with Combine.
My trouble is my StockDetailView is not receiving the updates from Combine and I can't see why. Below is a simplified version of the code for each view and viewModel. I think this has something to do with how I am assigning in the StockDetailViewModel but I can't figure it out. Any help would be appreciated.
StockListViewModel - Works Great
class StockListViewModel: ObservableObject {
#Published var stockRepository = StockRepository()
#Published var stockListCellViewModels = [StockListCellViewModel]()
private var cancellables = Set<AnyCancellable>()
init() {
stockRepository.$stocks.map { stocks in
stocks.map { stock in
StockListCellViewModel(stockDetailViewModel: StockDetailViewModel(stock: stock))
}
}
.assign(to: \.stockListCellViewModels, on: self)
.store(in: &cancellables)
}
}
StockListView - Works Great
struct StockListView: View {
#ObservedObject var stockRepository = StockRepository()
#ObservedObject var stockListVM = StockListViewModel()
var body: some View {
NavigationView {
List {
ForEach(stockListVM.stockListCellViewModels) { stockListCellVM in
NavigationLink(destination: StockDetailView(stockDetailVM: stockListCellVM.stockDetailViewModel)) {
StockListCell(stockListVM: stockListVM, stockListCellVM: stockListCellVM)
}
}
} // List
.listStyle(PlainListStyle())
.navigationBarTitle("stock")
} // NavigationView
} // View
}
StockListCellViewModel - Works Great
class StockListCellViewModel: ObservableObject, Identifiable {
var id: String = ""
#Published var stockDetailViewModel: StockDetailViewModel
#Published var stock: Stock
private var cancellables = Set<AnyCancellable>()
init(stockDetailViewModel: StockDetailViewModel) {
self.stockDetailViewModel = stockDetailViewModel
self.stock = stockDetailViewModel.stock
stockDetailViewModel.$stock.compactMap { stock in
stock.id
}
.assign(to: \.id, on: self)
.store(in: &cancellables)
stockDetailViewModel.$stock.map { stock in
StockDetailViewModel(stock: stock)
}
.assign(to: \.stockDetailViewModel, on: self)
.store(in: &cancellables)
}
}
StockListCellView - Works Great
struct StockListCell: View {
#ObservedObject var stockListVM: StockListViewModel
#ObservedObject var stockListCellVM: StockListCellViewModel
var body: some View {
Text(stockListCellVM.stock.ticker)
}
}
StockDetailViewModel - Not Updating
class StockDetailViewModel: ObservableObject, Identifiable {
var id: String = ""
#Published var stock: Stock
private var cancellables = Set<AnyCancellable>()
init(stock: Stock) {
self.stock = stock
self.chartColor = UIColor()
$stock.compactMap { stock in
stock.id
}
.assign(to: \.id, on: self)
.store(in: &cancellables)
}
StockDetailView - Not Updating
struct StockDetailView: View {
#ObservedObject var stockDetailVM: StockDetailViewModel
var body: some View {
Text(stockDetailVM.stock.ticker)
}
}

Answer 1

This took me the better part of two weeks to solve and I wanted to post it here for anyone experiencing the same issue I had. I rebuilt a simple example to make things easier to understand. Here is what the app does.
Connects to a Firestore database and starts a SnapShootListener to collect Note objects.
Once collected it stores the Notes, in an array of Note objects.
This array of notes is built into a List of notes.
Each note progresses to a NoteDetailView.
What I expected to happen was that as a Note was updated on the server, I would see the note update in real-time in the List and in the DetailView. My problem was that I could only see live updates in the List.
The reason for this is because you cannot bind a data element from a ForEach loop. This means that any updates made on the server never make it to the DetailView.
To solve this I introduced EnvironmentObjects and created DetailViews by passing the index of the Note to be shown in the DetailView to the DetailView. This allowed me to access the correct Note in the DetailView. The code below shows how this was done. NOTE: I did not added a NoteDetailViewModel.swift to simplify things.
<YOUR_PROJECT_NAME>App.swift
#main
struct ToDoSwiftUITutorialApp: App {
// 1. An #StateObject was created for the NoteRepository connected to Firestore.
#StateObject private var noteRepository = NoteRepository()
// Firebase
init() {
FirebaseApp.configure()
Auth.auth().signInAnonymously()
}
var body: some Scene {
WindowGroup {
ContentView()
.environmentObject(noteRepository) // noteRepository was added to ContentView as an EnvironmentObject.
}
}
}
NoteRepository.swift
class NoteRepository: ObservableObject {
let db = Firestore.firestore()
// Publishing the array of Note object received from Firestore.
#Published var notes = [Note]()
init() {
loadData()
}
func loadData() {
db.collection("notes").addSnapshotListener { (querySnapshot, error) in
if let querySnapshot = querySnapshot {
self.notes = querySnapshot.documents.compactMap { document in
do {
let x = try document.data(as: Note.self)
return x
}
catch {
print(error)
}
return nil
}
}
}
}
}
NoteListView.swift
struct NoteListView: View {
#ObservedObject var noteListViewModel = NoteListViewModel()
var body: some View {
NavigationView {
List {
ForEach(noteListViewModel.noteCellViewModels.indices, id: \.self) { index in
NavigationLink(destination: NoteDetailView(index: index).environmentObject(self.noteListViewModel)) {
NoteCellView(noteCellViewModel: noteListViewModel.noteCellViewModels[index])
} // NavigationLink
} // ForEach
}// List
.navigationBarTitle("Notes")
} // NavigationView
}
}
NoteListViewModel.swift
class NoteListViewModel: ObservableObject {
#Published var noteRepository = NoteRepository()
#Published var noteCellViewModels = [NoteCellViewModel]()
private var cancellables = Set<AnyCancellable>()
init() {
noteRepository.$notes.map { notes in
notes.map { note in
NoteCellViewModel(note: note)
}
}
.assign(to: \.noteCellViewModels, on: self)
.store(in: &cancellables)
}
}
NoteCellView.swift
struct NoteCellView: View {
#ObservedObject var noteCellViewModel: NoteCellViewModel
var body: some View {
Text(noteCellViewModel.note.note)
}
}
NoteCellViewModel.swift
class NoteCellViewModel: ObservableObject, Identifiable {
var id: String = ""
#Published var note: Note
private var cancellables = Set<AnyCancellable>()
init(note: Note) {
self.note = note
$note.compactMap { note in
note.id
}
.assign(to: \.id, on: self)
.store(in: &cancellables)
}
}
NoteDetailView.swift
struct NoteDetailView: View {
#EnvironmentObject var noteRepository: NoteRepository
var index: Int
var body: some View {
Text(noteRepository.notes[index].note)
}
}