9.12. SwiftUI Integration

Wire a ComponentVMOf<Model> to a SwiftUI view using @StateObject / @ObservedObject plus a tiny Combine adapter that bridges the VMx message hub into SwiftUI's ObservableObject machinery.

9.12.1. Reactivity primitive

SwiftUI re-renders when an ObservableObject publishes through its objectWillChange publisher. VMx VMs publish PropertyChangedMessage to their hub and emit a string-keyed propertyChanged Combine publisher. The adapter forwards every relevant event into objectWillChange.send().

9.12.2. Mapping

SwiftUI	VMx
@StateObject / @ObservedObject	wrapper around a ComponentVMOf<M>
objectWillChange.send()	hub PropertyChangedMessage subscription
Button(action: …)	command.execute()
.onDisappear { … }	cancel subscriptions / dispose VM

9.12.3. Adapter skeleton

import SwiftUI
import Combine
import VMx

final class TabAdapter<M>: ObservableObject {
    let vm: ComponentVMOf<M>
    private var cancellables: Set<AnyCancellable> = []

    init(_ vm: ComponentVMOf<M>) {
        self.vm = vm
        vm.propertyChanged
            .receive(on: RunLoop.main)
            .sink { [weak self] _ in self?.objectWillChange.send() }
            .store(in: &cancellables)
    }
}

struct TabContentView: View {
    @StateObject var adapter: TabAdapter<TabModel>

    var body: some View {
        VStack {
            Text(adapter.vm.model.title)
            Button("Save") { adapter.vm.selectCommand.execute() }
        }
        // `construct()` is throwing as of ADR-0053 (see §4). A legal
        // transition is the common path; `try?` discards the recoverable
        // `StatusTransitionError` an illegal/in-flight transition would throw.
        .onAppear { try? adapter.vm.construct() }
        .onDisappear { adapter.vm.dispose() }
    }
}

9.12.4. Lifecycle is throwing (ADR-0053)

As of the v3 convergence (ADR-0053, superseding ADR-0037 §2.5), the Swift lifecycle operations construct(), destruct(), and reconstruct() are throws — matching the catchable exceptions the C#/Python/TypeScript flavors already raise, instead of the earlier uncatchable preconditionFailure trap. An illegal transition (e.g. construct() on a disposed VM) or a concurrent re-invocation while a transition is in flight throws a catchable StatusTransitionError; the legal idempotent no-ops (construct from Constructed, destruct from Destructed) still return without throwing.

do {
    try adapter.vm.construct()
} catch let error as StatusTransitionError {
    // Recover — the VM is left in its prior settled state, not crashed.
    print("illegal lifecycle transition: \(error)")
}

A non-child current assignment likewise has a throwing companion (setCurrent(_:) throws, throwing CompositeMembershipError); see ADR-0053 §2.2.

9.12.5. Fuller example

The SwiftUI Notes Workspace flagship lives at examples/swift/notes-showcase/. Its NotesShowcaseCore target keeps the pure VM layer separate from SwiftUI, while the app target contains the Combine-to-SwiftUI binding bridge.

9.12.6. Cross-flavor parity

This recipe parallels the React adapter (react.md) — both bridge a hub message stream into the framework's "re-render this view" hook. The Avalonia (avalonia.md) and Textual (textual.md) recipes follow the same shape.