swiftui-patterns

name	swiftui-patterns
description	Patterns for SwiftUI apps using MVVM and `@Observable` (iOS 17+).
activation	Load when writing or reviewing SwiftUI views, state management, or UI code

Skill: swiftui-patterns

Overview

Patterns for SwiftUI apps using MVVM and @Observable (iOS 17+).

MVVM Architecture

• View: declarative SwiftUI struct. Observes ViewModel.
• ViewModel: @Observable class holding business logic and derived state.
• Model: plain struct value types. Immutable where possible.

State Management (iOS 17+)

• @Observable class — default for ViewModels. Properties are automatically tracked.
• @State — for ephemeral local View state only.
• @Binding — for two-way parent-child communication.
• @Environment / @EnvironmentValue — for global/shared dependencies (theme, analytics container).
• Legacy @ObservedObject and @StateObject are intentionally not covered by this skill.

View Lifecycle

• onAppear: one-time setup.
• task: preferred over onAppear + manual Task {} for async work. Auto-cancels on disappearance.
• onChange: react to specific value changes. Use with care to avoid infinite loops.

Previews

• Use #Preview macro. Include meaningful sample data.
• Never skip previews. They are the fastest feedback loop for UI.

Composition

• Decompose large Views into small, reusable subviews.
• Target ~50 lines max per View body.
• Extract complex expressions into private computed properties or subviews.

Separation of Concerns

• No business logic in View structs.
• Views should be thin declarative shells.
• Logic belongs in ViewModel or Service layers.