How to use nested ObservableObject in SwiftUI

Issue #694

I usually structure my app to have 1 main ObservableObject called Store with multiple properties in it.

final class Store: ObservableObject {
    @Published var pricingPlan: PricingPlan()
    @Published var preferences: Preferences()
}

struct Preferences {
    var opensAtLogin: Bool = true
}

final class PricingPlan: ObservableObject {
    @Published var isPro: Bool = true
}

SwiftUI for now does not work with nested ObservableObject, so if I pass Store to PricingView, changes in PricingPlan does not trigger view update in PricingView.

struct MainView: View {
    @ObservedObject
    var store: Store


    var body: some View {
        VStack { geo in
            
        }
        .sheet(isPresented: $showsPricing) {
            PricingView(
                isPresented: $showsPricing,
                store: store
            )
        }
    }
}

There are some workarounds

Pass nested ObservableObject

So that View observes both parent and nested objects.

PricingView(
    store: store,
    pricingPlan: store.pricingPlan
)

Use struct

This forces us to deal with immutability also, as with reference type PricingPlan, someone could just save a reference to it and alter it at some point.

struct PricingPlan {}

Listen to nested objects changes

Every ObservableObject has a synthesized property objectWillChange that triggers when any @Publisshed property changes

final class Store: ObservableObject {
    @Published var pricingPlan = PricingPlan()

    private var anyCancellable: AnyCancellable? = nil

    init() {
        anyCancellable = pricingPlan.objectWillChange.sink { [weak self] _ in
            self?.objectWillChange.send()
        }
    }