Controlling navigation with external state in SwiftUI

DataDrivenNavigation.swift

import SwiftUI
import Combine

enum Destination: Hashable {
    case a
    case b
    case c
}

class NavigationStore: BindableObject {
    let didChange = PassthroughSubject<Void, Never>()
    var currentDestination: Destination? = nil {
        didSet {
            didChange.send(())
        }
    }
}

struct ContentView : View {
    var body: some View {
        NavigationView {
            Root()
        }
    }
}


struct Root: View {
    
    @ObjectBinding var store: NavigationStore
    
    let link: DynamicNavigationDestinationLink<Destination, Destination, AnyView>
    
    init() {
        let store = NavigationStore()
        self.store = store
        self.link = DynamicNavigationDestinationLink(id: \.self) { destination -> AnyView? in
            switch destination {
            case .a: return AnyView(A(store: store))
            case .b: return AnyView(B(store: store))
            case .c: return AnyView(Root())
            }
        }
    }
    
    var body: some View {
        
        if link.presentedData?.value != store.currentDestination {
            link.presentedData?.value = store.currentDestination
        }
        
        return VStack(spacing: 10) {
            Button(action: { self.store.currentDestination = .a }) {
                Text("A")
            }
            Button(action: { self.store.currentDestination = .b }) {
                Text("B")
            }
            Button(action: { self.store.currentDestination = .c }) {
                Text("Push another root")
            }
        }
        .navigationBarTitle(Text("Root"))
    }
    
}

struct A: View {
    
    let store: NavigationStore
    
    var body: some View {
        VStack {
            Button(action: { self.store.currentDestination = nil }) {
                Text("Back")
            }
        }
        .navigationBarTitle(Text("A"))
    }
}

struct B: View {
    
    let store: NavigationStore
    
    var body: some View {
        VStack {
            Button(action: { self.store.currentDestination = nil }) {
                Text("Back")
            }
        }
        .navigationBarTitle(Text("B"))
    }
}