SwiftUI UI Patterns

Quick Start

Existing Project

1. Identify the feature and primary interaction model (list, detail, editor, settings, tabbed)
2. Find nearby examples in the repo with rg "TabView\(" or similar
3. Apply local conventions: prefer SwiftUI-native state, keep state local
4. Build with small, focused subviews and SwiftUI-native data flow

New Project Scaffolding

1. Wire TabView + NavigationStack + sheets
2. Add minimal AppTab enum and RouterPath
3. Expand route and sheet enums as new screens are added

General Rules

• Use modern SwiftUI state (@State, @Binding, @Observable, @Environment)
• Avoid unnecessary view models - prefer MV (Model-View) over MVVM
• Prefer composition; keep views small and focused
• Use async/await with .task and explicit loading/error states
• Follow the project's formatter and style guide

Sheets Best Practices

• Prefer .sheet(item:) over .sheet(isPresented:) when state represents a selected model
• Avoid if let inside a sheet body
• Sheets should own their actions and call dismiss() internally

Workflow for a New SwiftUI View

1. Define the view's state and its ownership location
2. Identify dependencies to inject via @Environment
3. Sketch the view hierarchy and extract repeated parts into subviews
4. Implement async loading with .task and explicit state enum if needed
5. Add accessibility labels or identifiers for interactive UI
6. Validate with a build and update usage callsites if needed

MV Pattern (Preferred over MVVM)

SwiftUI views should be lightweight state expressions. Avoid ViewModels unless truly necessary.

struct FeedView: View {
    @Environment(APIClient.self) private var client

    enum ViewState {
        case loading
        case error(String)
        case loaded([Post])
    }

    @State private var viewState: ViewState = .loading

    var body: some View {
        NavigationStack {
            List {
                switch viewState {
                case .loading:
                    ProgressView("Loading...")
                case .error(let message):
                    ErrorView(message: message, retry: { await loadFeed() })
                case .loaded(let posts):
                    ForEach(posts) { post in
                        PostRow(post: post)
                    }
                }
            }
            .task { await loadFeed() }
        }
    }

    private func loadFeed() async {
        do {
            let posts = try await client.getFeed()
            viewState = .loaded(posts)
        } catch {
            viewState = .error(error.localizedDescription)
        }
    }
}

Sheet Patterns

Item-driven sheet (preferred)

@State private var selectedItem: Item?

.sheet(item: $selectedItem) { item in
    EditItemSheet(item: item)
}

Sheet owns its actions

struct EditItemSheet: View {
    @Environment(\.dismiss) private var dismiss
    @Environment(Store.self) private var store

    let item: Item
    @State private var isSaving = false

    var body: some View {
        VStack {
            Button(isSaving ? "Saving..." : "Save") {
                Task { await save() }
            }
        }
    }

    private func save() async {
        isSaving = true
        await store.save(item)
        dismiss()
    }
}

App-Level Environment Setup

@main
struct MyApp: App {
    @State var client: APIClient = .init()
    @State var router: AppRouter = .init()

    var body: some Scene {
        WindowGroup {
            TabView(selection: $router.selectedTab) {
                ForEach(AppTab.allCases) { tab in
                    tab.rootView
                        .tag(tab)
                }
            }
            .environment(client)
            .environment(router)
        }
    }
}

State Management Guidelines

Wrapper	Use Case
@State	Local, ephemeral view state
@Binding	Two-way data flow from parent
@Observable	Shared state across views (iOS 17+)
@Environment	Dependency injection, app-wide concerns
@Query	SwiftData queries directly in views

Task and onChange Patterns

// React to state changes
.task(id: searchText) {
    guard !searchText.isEmpty else { return }
    await search(query: searchText)
}

// Respond to state transitions
.onChange(of: isActive, initial: false) {
    guard isActive else { return }
    Task { await refresh() }
}

Why Not MVVM?

SwiftUI was designed without ViewModels in mind:

• Views are structs, lightweight and disposable
• @State, @Environment, @Observable handle all data flow needs
• ViewModels add complexity, indirection, and cognitive overhead
• SwiftData's @Query works directly in views

Instead:

• Keep views as pure expressions of state
• Put business logic in services/models injected via @Environment
• Test services and models, not views
• Use SwiftUI Previews for visual regression testing