Swiftui Expert Skill

# SwiftUI Expert Skill

Overview

Use this skill to build, review, or improve SwiftUI features with correct state management, modern API usage, Swift concurrency best practices, optimal view composition, and iOS 26+ Liquid Glass styling. Prioritize native APIs, Apple design guidance, and performance-conscious patterns. This skill focuses on facts and best practices without enforcing specific architectural patterns.

When to Use This Skill

Use this skill when:

- Building new SwiftUI features

- Refactoring existing SwiftUI views

- Reviewing SwiftUI code quality

- Adopting modern SwiftUI patterns

- Working with SwiftUI state management

- Implementing iOS 26+ Liquid Glass styling

Workflow Decision Tree

1) Review existing SwiftUI code

- Check property wrapper usage against the selection guide (see `references/state-management.md`)

- Verify modern API usage (see `references/modern-apis.md`)

- Verify view composition follows extraction rules (see `references/view-structure.md`)

- Check performance patterns are applied (see `references/performance-patterns.md`)

- Verify list patterns use stable identity (see `references/list-patterns.md`)

- Inspect Liquid Glass usage for correctness and consistency (see `references/liquid-glass.md`)

- Validate iOS 26+ availability handling with sensible fallbacks

2) Improve existing SwiftUI code

- Audit state management for correct wrapper selection (prefer `@Observable` over `ObservableObject`)

- Replace deprecated APIs with modern equivalents (see `references/modern-apis.md`)

- Extract complex views into separate subviews (see `references/view-structure.md`)

- Refactor hot paths to minimize redundant state updates (see `references/performance-patterns.md`)

- Ensure ForEach uses stable identity (see `references/list-patterns.md`)

- Suggest image downsampling when `UIImage(data:)` is used (as optional optimization, see `references/image-optimization.md`)

- Adopt Liquid Glass only when explicitly requested by the user

3) Implement new SwiftUI feature

- Design data flow first: identify owned vs injected state (see `references/state-management.md`)

- Use modern APIs (no deprecated modifiers or patterns, see `references/modern-apis.md`)

- Use `@Observable` for shared state (with `@MainActor` if not using default actor isolation)

- Structure views for optimal diffing (extract subviews early, keep views small, see `references/view-structure.md`)

- Separate business logic into testable models (see `references/layout-best-practices.md`)

- Apply glass effects after layout/appearance modifiers (see `references/liquid-glass.md`)

- Gate iOS 26+ features with `#available` and provide fallbacks

Core Guidelines

State Management

- **Always prefer `@Observable` over `ObservableObject`** for new code

- **Mark `@Observable` classes with `@MainActor`** unless using default actor isolation

- **Always mark `@State` and `@StateObject` as `private`** (makes dependencies clear)

- **Never declare passed values as `@State` or `@StateObject`** (they only accept initial values)

- Use `@State` with `@Observable` classes (not `@StateObject`)

- `@Binding` only when child needs to **modify** parent state

- `@Bindable` for injected `@Observable` objects needing bindings

- Use `let` for read-only values; `var` + `.onChange()` for reactive reads

- Legacy: `@StateObject` for owned `ObservableObject`; `@ObservedObject` for injected

- Nested `ObservableObject` doesn't work (pass nested objects directly); `@Observable` handles nesting fine

Modern APIs

- Use `foregroundStyle()` instead of `foregroundColor()`

- Use `clipShape(.rect(cornerRadius:))` instead of `cornerRadius()`

- Use `Tab` API instead of `tabItem()`

- Use `Button` instead of `onTapGesture()` (unless need location/count)

- Use `NavigationStack` instead of `NavigationView`

- Use `navigationDestination(for:)` for type-safe navigation

- Use two-parameter or no-parameter `onChange()` variant

- Use `ImageRenderer` for rendering SwiftUI views

- U