SWIFTUI: Create Class with Array property - witch conform to 'ObservableObject'. Class! NOT struct

Question

I need to create Array property of class witch is conform to ObservableObject protocol. Because I am going to use it with filter, sort and etc - to select records from table to show in List view

class SQS_Record: NSObject, ObservableObject {
    @Published final var __idx: Int = -1 
}

class Project: SQS_Record {
    @objc dynamic var name: String = ""         { willSet { objectWillChange.send() } }
}

class SQS_Table<RecordType: SQS_Record>: ObservableObject {
    @Published var records = [RecordType]()
    var rcount: Int {
        return records.count
    }
    subscript (index: Int) -> RecordType {
        get {
            return records[index]
        }
        set(item) {
            records[index] = item
        }
    }


Let projectsTbl = SQS_Table<Project>(...)

struct ProjectsListView: View {
    // This is ERROR line - below
    @StateObject private var itemsList = projectsTbl.records.sorted { $0.__idx < $1.__idx }        
        
    var body: some View {
        NavigationView {
            List() {
                // Список
                ForEach (itemsList, id: \.__id) { (proj: Project) in
                    ProjectElement(project: proj)
                }
                .onMove(perform: moveItem )
                .onDelete(perform: delItem )
            }
    …
}

ERROR: Generic struct 'StateObject' requires that '[Project]' conform to 'ObservableObject'

Answer 1

If I understand your question correctly, the items of your array are classes. You could declare your array as @State, but only changes to the array itself (addition, sort, deletion) will cause the body to be recalculated.

Let's try :

struct ArrayOfObservableObjects: View {
    @State private var store = (1 ... 5).map(Record.init)
    var body: some View {
        NavigationView {
            List(store) { record in
                Text(record.score.description)
            }
            .toolbar {
                HStack {
                    Button("Shuffle") {
                        store.shuffle()
                    }
                    Button("Change First") {
                        store.first?.score = 666
                    }
                    Button("Add") {
                        store.insert(Record(store.count + 1), at: 0)
                    }
                }
            }
        }
    }
}

As you can see the "Change First" button actually changes the "score" of a "Record", but this modification is not displayed.

If you want the changes to each element of the array to be "published", you have to proceed in several steps:

1. Make your Records observable:

class Record: ObservableObject, Identifiable {
    let id = UUID()
    @Published var score: Int
    init(_ score: Int) {
        self.score = score
    }
}

2. wrap your array in an ObservableObject :

class RecordStore: ObservableObject {
    @Published var records: [Record] = (1 ... 5).map(Record.init)

3. subscribe to the changes on each element of the array

    private var c: AnyCancellable?
    init() {
        subscribeToChanges()
    }

    func subscribeToChanges() {
        c = records
            .publisher
            .flatMap { record in record.objectWillChange }
            .sink { [weak self] in
                self?.objectWillChange.send()
            }
    }
}

It works. But something is missing (if we add a new element it will not be observed). So to finish:

class RecordStore: ObservableObject {
    @Published var records: [Record] = (1 ... 5).map(Record.init) {
        didSet {
            subscribeToChanges()    ///<<< HERE
        }
    }

    private var c: AnyCancellable?
    init() {
        subscribeToChanges()
    }

    func subscribeToChanges() {
        c = records
            .publisher
            .flatMap { record in record.objectWillChange }
            .sink { [weak self] in
                self?.objectWillChange.send()
            }
    }
}

And the View :

import Combine
import SwiftUI

struct ArrayOfObservableObjects: View {
    @StateObject var store = RecordStore()
    var body: some View {
        NavigationView {
            List(store.records) { record in
                Text(record.score.description)
            }
            .toolbar {
                HStack {
                    Button("Shuffle") {
                        store.records.shuffle()
                    }
                    Button("Change First") {
                        store.records.first?.score = 666
                    }
                    Button("Add") {
                        store.records.insert(Record(store.records.count + 1), at: 0)
                    }
                }
            }
        }
    }
}