Fosmvvm Swiftui View Generator

FOSMVVM SwiftUI View Generator

Read shared/functional-discipline.md before proceeding. Every rule below derives from it.

Generate SwiftUI views that render FOSMVVM ViewModels.

Conceptual Foundation

For full architecture context, see FOSMVVMArchitecture.md | OpenClaw reference

API catalog: check ../shared/api-catalog/FOSMVVM.md § SwiftUI Support before hand-writing helpers.

In FOSMVVM, Views are thin rendering layers that display ViewModels:

┌─────────────────────────────────────────────────────────────┐
│                    ViewModelView Pattern                     │
├─────────────────────────────────────────────────────────────┤
│                                                              │
│  ViewModel (Data)          ViewModelView (SwiftUI)          │
│  ┌──────────────────┐     ┌──────────────────┐             │
│  │ title: String    │────►│ Text(vm.title)   │             │
│  │ items: [Item]    │────►│ ForEach(vm.items)│             │
│  │ isEnabled: Bool  │────►│ .disabled(!...)  │             │
│  └──────────────────┘     └──────────────────┘             │
│                                                              │
│  Operations (Actions)                                        │
│  ┌──────────────────┐     ┌──────────────────┐             │
│  │ submit()         │◄────│ Button(action:)  │             │
│  │ cancel()         │◄────│ .onAppear { }    │             │
│  └──────────────────┘     └──────────────────┘             │
│                                                              │
└─────────────────────────────────────────────────────────────┘

Key principle: Views don't transform or compute data. They render what the ViewModel provides.

← Functional discipline: the View has TWO inputs: the ViewModel (data, localized text) and the ratified design (layout, interaction — which also shapes WHICH VM properties exist, never their values); requirements project the operations that bind them. The sin is projecting content from the design, or projecting anything from an artifact without truth-layer standing.

View-ViewModel Alignment

The View filename should match the ViewModel it renders.

Sources/
  {ViewModelsTarget}/
    {Feature}/
      {Feature}ViewModel.swift        ←──┐
      {Entity}CardViewModel.swift     ←──┼── Same names
                                          │
  {ViewsTarget}/                          │
    {Feature}/                            │
      {Feature}View.swift             ────┤  (renders {Feature}ViewModel)
      {Entity}CardView.swift          ────┘  (renders {Entity}CardViewModel)

This alignment provides:

• Discoverability - Find the view for any ViewModel instantly
• Consistency - Same naming discipline across the codebase
• Maintainability - Changes to ViewModel are reflected in view location

Core Components

1. ViewModelView Protocol

Every view conforms to ViewModelView:

public struct MyView: ViewModelView {
    private let viewModel: MyViewModel

    public var body: some View {
        Text(viewModel.title)
    }

    public init(viewModel: MyViewModel) {
        self.viewModel = viewModel
    }
}

Required:

• private let viewModel: {ViewModel}
• public init(viewModel:)
• Conforms to ViewModelView protocol

2. Operations (Optional)

Display-only views skip this entire section. A View whose ViewModel has no operations property is display-only by definition — no Operations files exist on either side of the seam, no repaintToggle, no testDataTransporter. Do not invent an empty Operations protocol for symmetry; absence of operations is the signal that the View is display-only. (See "View Categories" below for the full distinction.)

Operations are an architectural seam

An Operations protocol is the framework-side analog of ServerRequest: a contract the View calls into without knowing who satisfies it. Three files participate, on two sides of the seam:

For a feature LandingPage, these live at:

• Sources/ViewModels/Operations/LandingPage/LandingPageOperations.swift
• Sources/ViewModels/Operations/LandingPage/LandingPageStubOps.swift
• Sources/{AppTarget}/Operations/LandingPage/LandingPageOps.swift

The View imports only the framework side and is unaware of which implementation runs. App Intents, lock-screen transport actions, and other non-View entry points dispatch through the same Operations protocol — the View is one entry point of several, not the owner of the action vocabulary.

Two protocol layers to keep distinct:

• FOSMVVM.ViewModelOperations — the framework's base protocol. Every per-feature operations protocol conforms to it.
• <Name>ViewModelOperations (e.g., LandingPageViewModelOperations) — your project's per-feature protocol; conforms to FOSMVVM.ViewModelOperations and lists the actions the View dispatches.

Generic over any at op method signatures

Per the architecture rule (no existentials at architectural boundaries), Operations method signatures take Fields conformers as generic parameters, not any:

// ✅ GOOD — generic specialization preserves the concrete type for the live op.
protocol ConversationOperations: ViewModelOperations {
    func create<F: ConversationFields>(from fields: F) async throws
}

// ❌ BAD — `any` erases the concrete type and pulls existentials through the call graph.
protocol ConversationOperations: ViewModelOperations {
    func create(from fields: any ConversationFields) async throws
}

Storage is a separate decision from method signatures. The View's operations property is typed as any <Name>ViewModelOperations — that's required, since Apple's API forces a concrete View struct shape and the View has to store the value somehow. This is the exception arch.md §1.5 explicitly carves out for "structural requirements that leave no alternative."

Crucially, any at storage does not infect the protocol's method signatures. Swift 5.7+ opens the existential implicitly at each call site, so a generic method called on an any P value still specializes to a concrete type at the call site:

private let operations: any ConversationOperations          // ← `any` at storage is fine

private func submit() async throws {
    try await operations.create(from: fields)              // ← F inferred concretely
}

The rule to internalize: any is acceptable at single-value storage sites; generics are required at protocol method signatures. The architecture's anti-existential pressure is about preventing erasure from compounding through the call graph — and a stored any P does not compound, because each method call re-specializes.

Server-backed example

Interactive views have operations:

public struct MyView: ViewModelView {
    private let viewModel: MyViewModel
    private let operations: any MyViewModelOperations

    #if DEBUG
    @State private var repaintToggle = false
    #endif

    public var body: some View {
        Button(action: performAction) {
            Text(viewModel.buttonLabel)
        }
        #if DEBUG
        .testDataTransporter(viewModelOps: operations, repaintToggle: $repaintToggle)
        #endif
    }

    public init(viewModel: MyViewModel) {
        self.viewModel = viewModel
        self.operations = viewModel.operations
    }

    private func performAction() {
        operations.performAction()
        toggleRepaint()
    }

    private func toggleRepaint() {
        #if DEBUG
        repaintToggle.toggle()
        #endif
    }
}

When views have operations:

• Store operations from viewModel.operations in init
• Add @State private var repaintToggle = false (DEBUG only)
• Add .testDataTransporter(viewModelOps:repaintToggle:) modifier (DEBUG only)
• Call toggleRepaint() after every operation invocation

Why toggleRepaint() exists. Client-hosted ops mutate @Observable storage that test harnesses (and occasionally SwiftUI itself) don't always re-observe in time for the next assertion. Toggling a @State flag forces a deterministic re-render at the View boundary, so UI tests see the post-op state instead of the pre-op state. In production builds the toggle is compiled out — it costs nothing at runtime.

Async vs sync op shape. Server-backed ops are typically async (try await operations.performAction()) and pair with the async Button forms — Button(error:action:) and its Localizable-titled twins — which deposit a thrown error into the screen's error: binding (add activity: for re-entry refusal, cancelTitle: for tap-to-cancel; see the FOSMVVM DocC article Async Actions and Error Presentation). For view-lifetime loads, use the .task(error:) twins — .task(error: $error) { try await loadData() }, or .task(id:error:) to restart the load when a value changes; a thrown error lands in the same binding, and cancellation (teardown, an id restart, or the CancellationError sentinel) never deposits into it (see the FOSMVVM DocC article Async Action Lifecycle and Cancellation). Client-hosted scalar-mutation ops are typically sync — the live op writes a property on @Observable storage and returns. Don't add async to an op method that doesn't need it; don't omit async on one that calls a ServerRequest.

The example above shows a server-backed op — operations.performAction() dispatches a ServerRequest. For client-hosted ops (those that mutate local @Observable storage), the call site shape is different — the View must inject storage from the environment and hand it to the op explicitly. See below.

2a. Client-Hosted Operations: @Environment Injection and output: at the Call Site

Applies when the ViewModel is client-hosted and its operations mutate one or more @Observable storage objects (e.g., UserSettings, DeviceState). Server-backed operations use the plain pattern shown in section 2.

Client-hosted ops take their write target as a trailing output storage: parameter. The ViewModel does not hold a reference to storage (see Architecture Patterns → VMs Hold Scalars); the View reads storage from @Environment and hands the reference to the op at the call site.

public struct PreferencesView: ViewModelView {
    // The reference to the @Observable lives on the View, not the ViewModel.
    @Environment(UserSettings.self) private var settings

    private let viewModel: PreferencesViewModel
    // Stored as `any` — required at View storage, see §2 "Generic over `any`".
    // The protocol's *method signatures* remain generic; existential opening
    // re-specializes at each call site.
    private let operations: any PreferencesViewModelOperations

    #if DEBUG
    @State private var repaintToggle = false
    #endif

    public var body: some View {
        VStack {
            Toggle(
                viewModel.notificationsLabel,
                isOn: Binding(
                    get: { viewModel.notificationsEnabled },
                    set: { setNotifications($0) }
                )
            )
            Picker(viewModel.themeLabel, selection: Binding(
                get: { viewModel.theme },
                set: { setTheme($0) }
            )) {
                // ... options
            }
        }
        #if DEBUG
        .testDataTransporter(viewModelOps: operations, repaintToggle: $repaintToggle)
        #endif
    }

    public init(viewModel: PreferencesViewModel) {
        self.viewModel = viewModel
        self.operations = viewModel.operations
    }

    private func setNotifications(_ enabled: Bool) {
        // Hand the reference from @Environment to the op at the call site.
        operations.setNotificationsEnabled(enabled, output: settings)
        toggleRepaint()
    }

    private func setTheme(_ theme: Theme) {
        operations.setTheme(theme, output: settings)
        toggleRepaint()
    }

    private func toggleRepaint() {
        #if DEBUG
        repaintToggle.toggle()
        #endif
    }
}

The mental model:

• @Environment(UserSettings.self) puts the reference on the View.
• The VM has scalars only (viewModel.notificationsEnabled: Bool, viewModel.theme: Theme), projected from settings by the parent's .bind(appState: .init(...)) call. The VM never holds the UserSettings reference.
• The mutation closure reads settings from its own @Environment and passes it to the op as output: settings. The reference never crosses the VM boundary.

Common mistakes to avoid:

Full rationale — why the VM holds scalars, why the reference flows through the call site rather than the VM, what breaks otherwise — lives in Architecture Patterns → Ops Conventions and Architecture Patterns → The Four Rules of Forward Projection.

3. Child View Binding

Parent views bind child views using .bind(appState:):

public struct ParentView: ViewModelView {
    @Environment(AppState.self) private var appState
    private let viewModel: ParentViewModel

    public var body: some View {
        VStack {
            Text(viewModel.title)

            // Bind child view with subset of parent's data
            ChildView.bind(
                appState: .init(
                    itemId: viewModel.selectedId,
                    isConnected: viewModel.isConnected
                )
            )
        }
    }
}

The .bind() pattern:

• Child views use .bind(appState:) to receive data from parent
• Parent creates child's AppState from its own ViewModel data
• Enables composition without tight coupling

4. Form Views with Validation

Forms use FormFieldView and Validations environment:

public struct MyFormView: ViewModelView {
    @Environment(Validations.self) private var validations
    @Environment(\.focusState) private var focusField
    @State private var error: Error?

    private let viewModel: MyFormViewModel
    private let operations: any MyFormViewModelOperations

    public var body: some View {
        Form {
            FormFieldView(
                fieldModel: viewModel.$email,
                focusField: focusField,
                fieldValidator: viewModel.validateEmail,
                validations: validations
            )

            Button(viewModel.submitButtonLabel, error: $error, action: submit)
                .disabled(validations.hasError)
        }
        .onSubmit {
            Task { do { try await submit() } catch { self.error = error } }
        }
        .alert(
            error: $error,
            title: viewModel.errorTitle,
            message: viewModel.errorMessage,
            dismissButtonLabel: viewModel.dismissButtonLabel
        )
    }
}

Form patterns:

• @Environment(Validations.self) for validation state
• FormFieldView for each input field
• Button(error:action:) (and its Localizable-titled twins) for async actions
• .disabled(validations.hasError) on submit button
• Separate handling for validation errors vs general errors

5. Previews

Use .previewHost() for SwiftUI previews:

#if DEBUG
#Preview {
    MyView.previewHost(
        bundle: MyAppResourceAccess.localizationBundle
    )
    .environment(AppState())
}

#Preview("With Data") {
    MyView.previewHost(
        bundle: MyAppResourceAccess.localizationBundle,
        viewModel: .stub(title: "Preview Title")
    )
    .environment(AppState())
}
#endif

View Categories

The first decision when generating a View is interactive vs. display-only — and that decision is forced by the ViewModel, not chosen by the View author.

Absence of operations is a positive signal that the View originates no actions. Inventing an empty Operations protocol "for symmetry" is an anti-pattern (arch.md §3.4).

Display-Only Views

Views that just render data (no user interactions):

public struct InfoView: ViewModelView {
    private let viewModel: InfoViewModel

    public var body: some View {
        VStack {
            Text(viewModel.title)
            Text(viewModel.description)

            if viewModel.isActive {
                Text(viewModel.activeStatusLabel)
            }
        }
    }

    public init(viewModel: InfoViewModel) {
        self.viewModel = viewModel
    }
}

Characteristics:

• No operations property
• No repaintToggle or testDataTransporter
• Just renders ViewModel properties
• May have conditional rendering based on ViewModel state

Interactive Views

Views with user actions:

public struct ActionView: ViewModelView {
    @State private var error: Error?

    private let viewModel: ActionViewModel
    private let operations: any ActionViewModelOperations

    #if DEBUG
    @State private var repaintToggle = false
    #endif

    public var body: some View {
        VStack {
            Button(action: performAction) {
                Text(viewModel.actionLabel)
            }

            Button(role: .cancel, action: cancel) {
                Text(viewModel.cancelLabel)
            }
        }
        .alert(
            error: $error,
            title: viewModel.errorTitle,
            message: viewModel.errorMessage,
            dismissButtonLabel: viewModel.dismissButtonLabel
        )
        #if DEBUG
        .testDataTransporter(viewModelOps: operations, repaintToggle: $repaintToggle)
        #endif
    }

    public init(viewModel: ActionViewModel) {
        self.viewModel = viewModel
        self.operations = viewModel.operations
    }

    private func performAction() {
        operations.performAction()
        toggleRepaint()
    }

    private func cancel() {
        operations.cancel()
        toggleRepaint()
    }

    private func toggleRepaint() {
        #if DEBUG
        repaintToggle.toggle()
        #endif
    }
}

Form Views

Views with validated input fields:

• Use FormFieldView for each input
• @Environment(Validations.self) for validation state
• Button disabled when validations.hasError
• Separate error handling for validation vs operation errors

Container Views

Views that compose child views:

public struct ContainerView: ViewModelView {
    @Environment(AppState.self) private var appState
    private let viewModel: ContainerViewModel
    private let operations: any ContainerViewModelOperations

    public var body: some View {
        VStack {
            switch viewModel.state {
            case .loading:
                ProgressView()

            case .ready:
                ChildAView.bind(
                    appState: .init(id: viewModel.selectedId)
                )

                ChildBView.bind(
                    appState: .init(
                        isActive: viewModel.isActive,
                        level: viewModel.level
                    )
                )
            }
        }
    }
}

When to Use This Skill

• Creating a new SwiftUI view for a FOSMVVM app
• Building UI to render a ViewModel
• Following an implementation plan that requires new views
• Creating forms with validation
• Building container views that compose child views

What This Skill Generates

Note: The corresponding ViewModel and ViewModelOperations should already exist (use fosmvvm-viewmodel-generator skill).

Project Structure Configuration

Pattern Implementation

This skill references conversation context to determine view structure:

View Type Detection

From conversation context, the skill identifies:

• ViewModel structure (from prior discussion or specifications read by Claude)
• View category: Display-only, interactive, form, or container
• Operations needed: Whether view has user-initiated actions
• Child composition: Whether view binds child views

Component Selection

Based on view type:

• Display-only: ViewModelView protocol, viewModel property only
• Interactive: Add operations, repaintToggle, testDataTransporter, toggleRepaint()
• Form: Add Validations environment, FormFieldView, validation error handling
• Container: Add child view .bind() calls

Code Generation

Generates view file with:

1. ViewModelView protocol conformance
2. Properties (viewModel, operations if needed, repaintToggle if interactive)
3. Body with rendering logic
4. Init storing viewModel and operations
5. Action methods (if interactive)
6. Test infrastructure (if interactive)
7. Previews for different states

Context Sources

Skill references information from:

• Prior conversation: Requirements discussed with user
• Specification files: If Claude has read specifications into context
• ViewModel definitions: From codebase or discussion

Key Patterns

Error Handling Pattern

The async Button forms own the catch: a thrown error lands in the error: binding (cleared on each launch), and one alert(error:) per screen presents it. The action closure is @Sendable () async throws — a thin dispatch into ops, never a hand-rolled do/catch:

@State private var error: Error?

var body: some View {
    VStack {
        Button(viewModel.submitLabel, error: $error) {
            try await operations.submit()
        }
    }
    .alert(
        error: $error,
        title: viewModel.errorTitle,
        message: viewModel.errorMessage,
        dismissButtonLabel: viewModel.dismissButtonLabel
    )
}

Add activity: $activity (an @State AsyncButtonActivity) to refuse re-entry while a run is in flight and to drive disabled(activity.isRunning); add cancelTitle: to make the button tap-to-cancel. See the FOSMVVM DocC article Async Actions and Error Presentation.

Validation Error Pattern

For forms, intercept validation failures inside the action and let everything else flow to the error: binding:

Button(viewModel.submitLabel, error: $error) {
    do {
        try await operations.submit(data: viewModel.data)
    } catch let responseError as MyRequest.ResponseError
        where !responseError.validationResults.isEmpty {
        await MainActor.run { validations.replace(with: responseError.validationResults) }
    }
}

Async Task Pattern

For view-lifetime loads, .task(error:) routes a thrown error into the screen's binding; cancellation — view teardown, an id: restart, or the CancellationError sentinel — never deposits into it:

var body: some View {
    VStack {
        if isLoading {
            ProgressView()
        } else {
            contentView
        }
    }
    .task(error: $error) {
        try await loadData()
    }
}

private func loadData() async throws {
    isLoading = true
    try await operations.loadData()
    isLoading = false
    toggleRepaint()
}

To restart the load when a value changes, key it: .task(id: viewModel.selectedId, error: $error) { ... } — the superseded invocation writes nothing to the binding. The lifecycle semantics are drawn situation-by-situation in the FOSMVVM DocC article Async Action Lifecycle and Cancellation.

Conditional Rendering Pattern

Use ViewModel state for conditionals:

var body: some View {
    VStack {
        if viewModel.isEmpty {
            Text(viewModel.emptyStateMessage)
        } else {
            ForEach(viewModel.items) { item in
                ItemRow(item: item)
            }
        }
    }
}

Computed View Components Pattern

Extract reusable view fragments as computed properties:

private var headerView: some View {
    HStack {
        Text(viewModel.title)
        Spacer()
        Image(systemName: viewModel.iconName)
    }
}

var body: some View {
    VStack {
        headerView
        contentView
    }
}

Result/Error Handling Pattern

When a view needs to render multiple possible ViewModels (success, various error types), use an enum wrapper:

The Wrapper ViewModel:

@ViewModel
public struct TaskResultViewModel {
    public enum Result {
        case success(TaskViewModel)
        case notFound(NotFoundViewModel)
        case validationError(ValidationErrorViewModel)
        case permissionDenied(PermissionDeniedViewModel)
    }

    public let result: Result
    public var vmId: ViewModelId = .init(type: Self.self)

    public init(result: Result) {
        self.result = result
    }
}

The View:

public struct TaskResultView: ViewModelView {
    private let viewModel: TaskResultViewModel

    public var body: some View {
        switch viewModel.result {
        case .success(let vm):
            TaskView(viewModel: vm)
        case .notFound(let vm):
            NotFoundView(viewModel: vm)
        case .validationError(let vm):
            ValidationErrorView(viewModel: vm)
        case .permissionDenied(let vm):
            PermissionDeniedView(viewModel: vm)
        }
    }

    public init(viewModel: TaskResultViewModel) {
        self.viewModel = viewModel
    }
}

Key principles:

• Each error scenario has its own ViewModel type
• The wrapper enum associates specific ViewModels with each case
• The view switches on the enum and renders the appropriate child view
• Maintains type safety (no any ViewModel existentials)
• No generic error handling - each error type is specific and meaningful

ViewModelId Initialization - CRITICAL

IMPORTANT: ViewModelId controls SwiftUI's view identity system via the .id(vmId) modifier. Incorrect initialization causes SwiftUI to treat different data as the same view, breaking updates.

❌ WRONG - Never use this:

public var vmId: ViewModelId = .init()  // NO! Generic identity

✅ MINIMUM - Use type-based identity:

public var vmId: ViewModelId = .init(type: Self.self)

This ensures views of the same type get unique identities.

✅ IDEAL - Use data-based identity when available:

public struct TaskViewModel {
    public let id: ModelIdType
    public var vmId: ViewModelId

    public init(id: ModelIdType, /* other params */) {
        self.id = id
        self.vmId = .init(id: id)  // Ties view identity to data identity
        // ...
    }
}

Why this matters:

• SwiftUI uses .id() modifier to determine when to recreate vs update views
• vmId provides this identity for ViewModelViews
• Wrong identity = views don't update when data changes
• Data-based identity (.init(id:)) is best because it ties view lifecycle to data lifecycle

File Organization

Sources/{ViewsTarget}/
├── {Feature}/
│   ├── {Feature}View.swift             # Full page → {Feature}ViewModel
│   ├── {Entity}CardView.swift          # Child component → {Entity}CardViewModel
│   ├── {Entity}RowView.swift           # Child component → {Entity}RowViewModel
│   └── {Modal}View.swift               # Modal → {Modal}ViewModel
├── Shared/
│   ├── HeaderView.swift                # Shared components
│   └── FooterView.swift
└── Styles/
    └── ButtonStyles.swift              # Reusable button styles

Common Mistakes

Computing Data in Views

// ❌ BAD - View is transforming data
var body: some View {
    Text("\(viewModel.firstName) \(viewModel.lastName)")
}

// ✅ GOOD - ViewModel provides shaped result
var body: some View {
    Text(viewModel.fullName)  // via @LocalizedCompoundString
}

Forgetting to Call toggleRepaint()

// ❌ BAD - Test infrastructure won't work
private func submit() {
    operations.submit()
    // Missing toggleRepaint()!
}

// ✅ GOOD - Always call after operations
private func submit() {
    operations.submit()
    toggleRepaint()
}

Using Computed Properties for Display

// ❌ BAD - View is computing
var body: some View {
    if !viewModel.items.isEmpty {
        Text("You have \(viewModel.items.count) items")
    }
}

// ✅ GOOD - ViewModel provides the state
var body: some View {
    if viewModel.hasItems {
        Text(viewModel.itemCountMessage)
    }
}

Hardcoding Text

// ❌ BAD - Not localizable
Button(action: submit) {
    Text("Submit")
}

// ✅ GOOD - ViewModel provides localized text
Button(action: submit) {
    Text(viewModel.submitButtonLabel)
}

The rule covers operation arguments, not just display (ratified 2026-08-25): prose handed into an operation persists and renders back in every locale, so it too arrives from the user or from the ViewModel — never as a view-body literal. Even a deliberate default name is a product decision sited on the VM, localized:

// ❌ BAD — an English literal, persisted and displayed forever after
try await operations.createCard(title: "New Card", mvvmEnv: mvvmEnv)

// ✅ GOOD — the localized default is the ViewModel's
try await operations.createCard(title: viewModel.newCardDefaultTitle, mvvmEnv: mvvmEnv)

(User-authored input the view conduits, typed values that localize at render, and machine text — identifiers, testing tags, query syntax — are not prose.)

Missing Error Binding

// ❌ BAD - Errors not handled
Button(action: submit) {
    Text(viewModel.submitLabel)
}

// ✅ GOOD - Error binding for async actions
Button(viewModel.submitLabel, error: $error, action: submit)

Storing Operations in Body Instead of Init

// ❌ BAD - Recomputed on every render
public var body: some View {
    let operations = viewModel.operations
    Button(action: { operations.submit() }) {
        Text(viewModel.submitLabel)
    }
}

// ✅ GOOD - Store in init
private let operations: any MyOperations

public init(viewModel: MyViewModel) {
    self.viewModel = viewModel
    self.operations = viewModel.operations
}

Mismatched Filenames

// ❌ BAD - Filename doesn't match ViewModel
ViewModel: TaskListViewModel
View:      TasksView.swift

// ✅ GOOD - Aligned names
ViewModel: TaskListViewModel
View:      TaskListView.swift

Incorrect ViewModelId Initialization

// ❌ BAD - Generic identity, views won't update correctly
public var vmId: ViewModelId = .init()

// ✅ MINIMUM - Type-based identity
public var vmId: ViewModelId = .init(type: Self.self)

// ✅ IDEAL - Data-based identity (when id available)
public init(id: ModelIdType) {
    self.id = id
    self.vmId = .init(id: id)
}

Force-Unwrapping Localizable Strings

// ❌ BAD - Force-unwrapping to work around missing overload
import SwiftUI

Text(try! viewModel.title.localizedString)  // Anti-pattern - don't do this!
Label(try! viewModel.label.localizedString, systemImage: "star")

// ✅ GOOD - Request the proper SwiftUI overload instead
// The correct solution is to add an init extension like this:
extension Text {
    public init(_ localizable: Localizable) {
        self.init(localizable.localized)
    }
}

extension Label where Title == Text, Icon == Image {
    public init(_ title: Localizable, systemImage: String) {
        self.init(title.localized, systemImage: systemImage)
    }
}

// Then views use it cleanly without force-unwraps:
Text(viewModel.title)
Label(viewModel.label, systemImage: "star")

Why this matters:

FOSMVVM provides the Localizable protocol for all localized strings and includes SwiftUI init overloads for common elements like Text. However, not every SwiftUI element has a Localizable overload yet.

When you encounter a SwiftUI element that doesn't accept Localizable directly:

1. DON'T work around it with try! localizable.localizedString - this bypasses the type system and spreads force-unwrap calls throughout the view code
2. DO request that we add the proper init overload to FOSUtilities for that SwiftUI element
3. The pattern is simple: Extensions that accept Localizable and pass .localized to the standard initializer

This approach keeps the codebase clean, type-safe, and eliminates force-unwraps from view code entirely.

File Templates

See reference.md for complete file templates.

Naming Conventions

Common Modifiers

FOSMVVM-Specific Modifiers

// Error alert with ViewModel strings
.alert(
    error: $error,
    title: viewModel.errorTitle,
    message: viewModel.errorMessage,
    dismissButtonLabel: viewModel.dismissButtonLabel
)

// Async task — errors route into the same binding; cancellation never deposits
.task(error: $error) {
    try await loadData()
}

// Keyboard submit routing into the same binding
.onSubmit {
    Task { do { try await submit() } catch { self.error = error } }
}

// Test data transporter (DEBUG only)
.testDataTransporter(viewModelOps: operations, repaintToggle: $repaintToggle)

// UI testing identifier
.uiTestingIdentifier("submitButton")

A tag may span a composite — a row holding a caption and a field is a natural authoring unit, and tests read and tap the control the composite contains. When a composite holds several controls, the first in document order answers, so tag the control itself to address one precisely.

Standard SwiftUI Modifiers

Apply standard modifiers as needed for layout, styling, etc.

How to Use This Skill

Invocation:

/fosmvvm-swiftui-view-generator

Prerequisites:

• ViewModel and its structure are understood from conversation
• Optionally, specification files have been read into context
• View requirements (display-only, interactive, form, container) are clear from discussion

Output:

• {ViewName}View.swift - SwiftUI view conforming to ViewModelView protocol

Workflow integration: This skill is typically used after discussing requirements or reading specification files. The skill references that context automatically—no file paths or Q&A needed.

See Also

• Architecture Patterns - Mental models and patterns
• FOSMVVMArchitecture.md - Full FOSMVVM architecture
• fosmvvm-viewmodel-generator - For creating ViewModels
• fosmvvm-ui-tests-generator - For creating UI tests
• reference.md - Complete file templates

Version History