Android

Much of what older books and tutorials describe predates this timeline: Eclipse/ADT, JCenter, AsyncTask and Loaders, Kotlin synthetics, startActivityForResult, and LiveData-first, Views-only architectures. These pages document the current approach and name the older one only where a reader is likely to meet it in an existing codebase — see Books and official sources compared below for the full list.

If TrailMate will be a Compose app: Getting Started with Android → Project Structure, Gradle and Build Variants → Jetpack Compose Fundamentals → Compose Layouts, Modifiers and Lazy Lists → State, Recomposition and Side Effects in Compose → Recommended App Architecture → ViewModel, Lifecycle-Aware Components, Coroutines and Flow → Navigation in Compose.

If TrailMate is an existing View-based app instead: Activities and the Activity Lifecycle → Fragments and the Fragment Lifecycle → Views, XML Layouts, View Binding and Material Components → Saving UI State: Views vs. Compose → Views, Fragments and Activities vs. Compose: Architecture Comparison → Migrating from Views to Compose.

From there, pick the groups in What’s covered below in whatever order the app needs them: data and networking once it has something to store or fetch, system integration once it runs on a real device, and the quality and distribution pages before the first release.

Every code example across pages 1—​36 is a slice of one running app, TrailMate: a hiking-trail companion, package com.example.trailmate, that lists trails, shows their detail and lets a hiker mark favorites and capture photos. Its domain is small on purpose: Trail(id, name, region, lengthKm, difficulty, photoUrl, isFavorite), enum class Difficulty { EASY, MODERATE, HARD } and TrailPhoto.

TrailMate is built twice across these pages, in the two UI styles this section covers: a modern version with a single ComponentActivity, TrailMateApp() and Compose screens (TrailListScreen/TrailDetailScreen/SettingsScreen/PhotoCaptureScreen), and a legacy version with an AppCompatActivity hosting a NavHostFragment and TrailListFragment/TrailDetailFragment built with RecyclerView, ViewBinding and Safe Args. Both versions share the same data layer: a Retrofit-backed TrailApi (with a Ktor TrailApiClient shown as an alternative) against https://api.example.com/v1/trails, a Room TrailMateDatabase and a DataStore-backed UserPreferencesRepository, unified behind a TrailRepository interface implemented by OfflineFirstTrailRepository. A TrailSyncWorker keeps data fresh in the background, and a RecordHikeService foreground service tracks an active hike. Dependency injection is shown with both Hilt (TrailMateApplication, NetworkModule, DatabaseModule, RepositoryModule) and a Koin alternative (trailMateModule); images load through Coil in Compose and Glide in the legacy code. The app is split into Gradle modules :app, :core:model, :core:data, :core:database, :core:network, :feature:trails and :feature:settings, and is exercised by tests such as TrailListViewModelTest, OfflineFirstTrailRepositoryTest, TrailDaoTest and TrailListScreenTest.

Pages 37—​40 (building, signing, publishing and CI/CD) step away from TrailMate and use a real, published library instead — com.irurueta:irurueta-android-glutils — so that the build, signing and Maven Central publishing steps are shown against an actual build.gradle.kts and GitHub Actions workflow rather than a fictional one.

Six books were read locally against the concepts documented here, purely to decide what to cover and to check for gaps — none of them is quoted or copied into this repository.

Legend for the matrix below: full = the concept has a chapter or main section in that book; partial = partial coverage, or an older API for the same concept; none = not covered. The Official Android Developers documentation is the primary source behind every page regardless of book coverage.

Concepts found mostly in the books, folded into an existing page rather than given a page of their own: LeakCanary, Chucker, ktlint and detekt (B1, page 36); Firebase Crashlytics and Cloud Messaging (B1, pages 36 and 30); RxJava versus coroutines (B3/B4, page 20, as legacy); Data Binding (B3, page 7, as legacy); MotionLayout and CoordinatorLayout (B3/B6, page 9); Moshi (B3, page 26); Bluetooth, NFC, USB and WebView (B5, page 32); content providers (B5/B6, page 3); AppWidgets (B5, page 30); and NDK/RenderScript (B5, page 33, with RenderScript named as deprecated).

Official concepts documented from the official sources alone, with no book coverage: Navigation 3, adaptive layouts and window size classes, edge-to-edge and predictive back, the targetSdk 36/37 large-screen rules, Credential Manager, Baseline Profiles and Macrobenchmark, AGP 9’s built-in Kotlin and its new DSL, KSP2, Room 3, the photo picker, the Compose testing APIs, UI Automator 2.4, the Central Publisher Portal and the vanniktech plugin, Play developer verification, the 16 KB page-size rule, Coil 3 and Glide 5.

Outdated book material is named only as legacy, each with the modern replacement used on the matching page: Eclipse/ADT (Android Studio), JCenter (Maven Central), OSSRH (the Central Publisher Portal), kapt (KSP), Kotlin synthetics (View Binding), AsyncTask/Loaders (coroutines), IntentService (WorkManager), onRetainNonConfigurationInstance (ViewModel), ListView (RecyclerView/LazyColumn), RenderScript (Vulkan/AGSL), startActivityForResult (the Activity Result API), onBackPressed() (OnBackPressedCallback), Picasso (Coil), and LiveData-first design (StateFlow).

This section builds on material documented elsewhere on this site rather than repeating it. The Kotlin Reference covers the language every example is written in — including coroutines, flows and Kotlin for Android itself. Kotlin Multiplatform shares Kotlin code (and, with Compose Multiplatform, UI) between this TrailMate app and iOS, desktop and the web. React Native is the cross-platform alternative that targets Android and iOS from one TypeScript codebase, and Apple Platforms is the native counterpart on Google’s rival ecosystem, covering iOS, iPadOS, macOS, watchOS and visionOS with Swift and SwiftUI. Native and Mobile Apps is the OAuth protocol reference behind this section’s Credential Manager and sign-in material, Git & GitHub underlies the version control and pull-request workflow assumed on the CI/CD page, and Docker covers the containers that back the emulator and backend services a real TrailMate deployment would run against.