android-architecture

Android Architecture

Overview

Provide opinionated architecture guidance for modern Android apps built with Kotlin and Jetpack Compose. Follow convention-over-configuration: recommend proven defaults and explain when alternatives make sense. All guidance targets Compose-first, Kotlin-only development using official Jetpack libraries.

Disclaimer: This skill provides educational guidance for learning Android development. For production apps handling sensitive user data, payment processing, authentication, or security-critical features, consult a professional Android developer or security auditor.

Philosophy

• Convention over configuration — pick the right default so users don't have to choose
• Official Jetpack libraries first — prefer Google-maintained solutions over third-party
• Compose-first, Kotlin-only — no XML layouts or Java for new projects
• Teach the "why" — every pattern explained, not just pasted

Architecture Decision Table

Use this to recommend the right level of architecture based on app complexity:

App Complexity	Architecture	DI	Data Layer	Navigation
Simple (1-3 screens, local data)	Single-module MVVM	Manual or Hilt	Room or DataStore	Jetpack Navigation 3
Medium (4-10 screens, network + local)	Multi-module MVVM	Hilt	Repository pattern, Room + Retrofit	Jetpack Navigation 3
Complex (10+ screens, multiple data sources)	Clean Architecture with MVVM	Hilt	Use case layer, Repository pattern	Jetpack Navigation 3, type-safe routes

Standard Project Structure

Recommend this package layout for medium-complexity apps:

com.example.myapp/
├── data/
│   ├── local/          # Room database, DAOs, entities
│   ├── remote/         # Retrofit services, DTOs
│   └── repository/     # Repository implementations
├── di/                 # Hilt modules
├── domain/             # (Clean Architecture only) Use cases, domain models
├── ui/
│   ├── components/     # Reusable Compose components
│   ├── navigation/     # Navigation graph, routes
│   ├── screens/        # Screen composables + ViewModels
│   └── theme/          # Material 3 theme, colors, typography
└── util/               # Extension functions, constants

For simple apps, flatten data/ and skip domain/.

Technology Selection Matrix

Need	Default Choice	Alternative	When to Switch
Architecture	MVVM	MVI	Complex state machines, heavy user interaction flows
Dependency Injection	Hilt	Koin	Kotlin Multiplatform projects, or personal preference
Networking	Retrofit + OkHttp	Ktor	Kotlin Multiplatform shared networking
Local Database	Room	SQLDelight	Kotlin Multiplatform shared database
Key-Value Storage	DataStore (Preferences)	—	Always use DataStore; SharedPreferences is legacy
Image Loading	Coil	Glide	Existing project already using Glide
Serialization	Kotlin Serialization	Moshi, Gson	Moshi for Java interop; Gson is legacy
UI Framework	Jetpack Compose	XML Views	Only for maintaining existing XML codebases

Kotlin Multiplatform Awareness

If the user mentions KMP, Compose Multiplatform, or shared logic:

• Use Ktor instead of Retrofit for networking
• Use SQLDelight instead of Room for databases
• Use Koin instead of Hilt for DI (Hilt is Android-only)
• Shared ViewModels are possible with KMP-ViewModel
• This plugin covers Android-native; for full KMP guidance, recommend official KMP documentation

Common Architecture Mistakes

Mistake	Why It's Wrong	Correct Approach
Business logic in Composables	Untestable, survives recomposition poorly	Move to ViewModel
ViewModel calling DAO directly	Tight coupling, hard to test	Use Repository pattern
Passing ViewModel to child Composables	Couples UI tree to specific ViewModel	Pass state and callbacks down
Using GlobalScope for coroutines	Leaks, not lifecycle-aware	Use viewModelScope or lifecycleScope
Storing UI state in remember across config changes	Lost on rotation	Use ViewModel + StateFlow
Network calls on Main thread	ANR (Application Not Responding)	Dispatchers.IO via Repository

References

• references/project-setup-guide.md — Step-by-step new project walkthrough with Android Studio setup
• references/architecture-patterns.md — MVVM and Clean Architecture with full code examples
• references/dependency-injection.md — Hilt setup, modules, scoping, and testing patterns