ui-patterns
Best practices and patterns for building SwiftUI views and components. Use when creating or refactoring SwiftUI UI, designing tab architecture, composing screens, or needing component-specific guidance.
What this skill does
# 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.
```swift
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)
```swift
@State private var selectedItem: Item?
.sheet(item: $selectedItem) { item in
EditItemSheet(item: item)
}
```
### Sheet owns its actions
```swift
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
```swift
@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
```swift
// 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
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