Android Java Skill Project Structure Gradle Configuration App level build.gradle Architecture Patterns MVVM with ViewModel Repository Pattern Activity & Fragment Patterns Activity with ViewBinding Fragment with ViewBinding Testing Unit Tests with JUnit & Mockito Instrumentation Tests with Espresso GitHub Actions Lint Configuration lint.xml build.gradle lint options Common Patterns Null Safe Callbacks Safe Context Usage Thread Safe Singleton Android Anti Patterns ❌ Context leaks Never hold Activity/Fragment references in static fields or singletons ❌ Memory leaks in callbacks Always use WeakReference or clear callbacks in onDestroy ❌ UI updates on background thread Always post to main thread for UI changes ❌ Hardcoded strings Use string resources for all user visible text ❌ God Activities Keep Activities under 200 lines, extract logic to ViewModels ❌ NetworkOnMainThreadException Never perform network calls on main thread ❌ Ignoring lifecycle Always respect Activity/Fragment lifecycle states ❌ Blocking the main thread Keep main thread operations under 16ms ❌ Not handling configuration changes Use ViewModel to survive rotation ❌ Hardcoded dimensions Use dp/sp units and dimension resources ❌ Deep view hierarchies Keep layout depth under 10 levels, use ConstraintLayout ❌ Not closing resources Always close Cursor, InputStream, database connections

android-java