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name: swiftui-mvvm-pattern version: 0.1.0 author: cmtzco description: iOS SwiftUI MVVM architectural pattern implementation guide. When to use: when creating new views, implementing data binding between UI and business logic, adding screens to SwiftUI apps, or working with state management in iOS. What problems it solves: provides clear separation of concerns, enables reusable business logic, makes state management predictable with @Published properties, and follows iOS best practices for SwiftUI apps.

SwiftUI MVVM Pattern

Overview

The Model-View-ViewModel (MVVM) pattern is standard architectural approach for SwiftUI applications. This skill guides you through implementing ViewModels that expose @Published properties, Views that use @StateObject to inject ViewModels, and proper data flow between the two layers.

Identified Patterns

The following patterns were identified in this codebase that this skill addresses:

Pattern 1: ObservableObject ViewModel

• Location: DadBrain/DadBrain/ViewModels/MemoryListViewModel.swift
• Description: Class conforming to ObservableObject with @Published properties for state management
• Frequency: Found in 5 ViewModels (MemoryListViewModel, VoiceRecorder, PhotoScanner, KeywordExtractor, MemorySummarizer)

Pattern 2: @StateObject View Injection

• Location: DadBrain/DadBrain/Views/MemoriesListView.swift
• Description: SwiftUI Views using @StateObject to create and own ViewModels
• Frequency: Found in 7 View files using consistent injection pattern

Pattern 3: @Environment Object Dependency Injection

• Location: DadBrain/DadBrain/Views/MemoriesListView.swift
• Description: Using @Environment for shared dependencies like Core Data contexts
• Frequency: Used across multiple views for PersistenceController

TODO: Implementation

This skeleton skill needs Phase 2 refinement. Areas to develop:

Workflow Instructions

1. Create ViewModel class with ObservableObject
2. Add @Published properties for observable state
3. Create View with @StateObject injection
4. Bind View UI to ViewModel properties
5. Handle user actions in ViewModel methods

Best Practices

• When to use @StateObject vs @ObservedObject
• Dependency injection patterns
• Testing ViewModels in isolation
• Handling async operations in ViewModels

Common Pitfalls

• Memory leaks with improper object lifecycle
• State synchronization issues
• Over-complicating ViewModels with view logic
• Missing @Published on properties that should trigger updates

Suggested Resources

Based on codebase analysis, consider adding:

Scripts (scripts/)

• mvvm-viewmodel-generator.swift - Generates ViewModel boilerplate from entity definitions
• mvvm-view-generator.swift - Creates View scaffolds with proper StateObject injection

References (references/)

• apple-swiftui-data-flow.md - Apple's official documentation on data flow
• stateobject-vs-observedobject.md - When to use each property wrapper
• mvvm-testing-patterns.md - Testing strategies for ViewModels

Assets (assets/)

• viewmodel-templates/ - Swift templates for different ViewModel scenarios
• view-templates/ - SwiftUI View templates with MVVM structure

Evidence from Codebase

Refinement Priority

Score: 8.4/10 Priority: High

Refinement Tasks

1. Research Apple's SwiftUI data flow documentation
2. Create mvvm-viewmodel-generator script
3. Document state management patterns and property wrappers
4. Add examples from MemoryListViewModel and other ViewModels
5. Create testing guide for ViewModels

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Skeleton generated by ContextHarness /baseline Run Phase 2 skill refinement to complete implementation