swiftui-data-flow-expert

license	Apache-2.0
name	swiftui-data-flow-expert
description	SwiftUI data flow expert with @Observable, SwiftData, NavigationStack, and structured concurrency. Activate on: SwiftUI state management, @Observable, SwiftData, NavigationStack, Combine, async/await Swift, structured concurrency, MVVM SwiftUI. NOT for: UIKit legacy (use react-native-architect), Core Data migrations (use ios-core-data-architect), Android Compose (use jetpack-compose-navigation-expert).
allowed-tools	Read,Write,Edit,Bash(swift:*,xcodebuild:*)
category	Mobile Development
tags	["swiftui","ios","swift","state-management"]
pairs-with	[{"skill":"native-app-designer","reason":"Native design patterns inform SwiftUI component architecture"},{"skill":"ios-core-data-architect","reason":"Core Data and SwiftData persistence layer beneath SwiftUI views"}]

SwiftUI Data Flow Expert

Expert in SwiftUI state management with @Observable, SwiftData persistence, NavigationStack, and structured concurrency patterns for iOS 17+/18.

Decision Points

State Management Choice

1. View-local state (form inputs, toggles, local UI)?
   → Use @State
   → Keep data inside the view
   → Example: @State private var showingSheet = false

2. Shared state across views (user session, app data)?
   → Use @Observable class
   → Pass via @Environment or init
   → Example: @Observable class UserSession

3. Persistent data (saved to disk)?
   → Use SwiftData @Model
   → Access via @Query in views
   → Example: @Model class Expense

4. External data source (network, sensors)?
   → Use @Observable + async methods
   → Wrap in Task {} for concurrency
   → Example: @Observable class WeatherViewModel

Concurrency Model Choice

1. Single async operation (network call)?
   → Use Task {} in SwiftUI .task modifier
   → Handle errors with do/catch

2. Multiple related operations?
   → Use TaskGroup for parallel execution
   → Use await for sequential dependencies

3. Continuous data stream (location, sensors)?
   → Use AsyncStream or AsyncSequence
   → Cancel with .onDisappear

4. Background processing?
   → Use @globalActor or custom actor
   → Never access @MainActor data directly

Data Binding Strategy

1. Direct property binding needed?
   → Use @Bindable(viewModel)
   → Allows $ syntax for Observable objects

2. One-way data flow only?
   → Pass Observable directly
   → Read properties without $

3. Computed property or transformation?
   → Create computed var in Observable class
   → SwiftUI auto-tracks changes

4. Form data with validation?
   → Use @State for working copy
   → Sync to Observable on save/submit

Failure Modes

Symptom: View Won't Re-render

• Detection: Data changes but UI stays stale
• Diagnosis: Missing observation or wrong binding type
• Fix: Ensure @Observable class, check @Bindable usage, verify property access

Symptom: App Crashes on Navigation

• Detection: Fatal error on NavigationLink tap or back navigation
• Diagnosis: Type mismatch in NavigationStack routing
• Fix: Verify navigationDestination(for:) matches NavigationLink value types

Symptom: Data Appears Then Disappears

• Detection: SwiftData @Query shows data briefly, then empty list
• Diagnosis: ModelContext not properly injected or predicate filtering all results