JetpackCrypto

A real-time cryptocurrency price tracker built as a step-by-step teaching project for Android Jetpack. The app fetches the top coins from the CoinGecko API and displays them in a live, paginated list with a detail screen for each coin.

Each class maps to a branch. Checkout any branch to see the app at that exact stage of the course.

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What the App Does

• Fetches the top 100 cryptocurrencies from CoinGecko (no API key required)
• Displays a paginated list with coin name, symbol, logo, and current USD price
• Tapping a coin opens a detail screen with 24h high/low and price change
• Background price refresh via WorkManager every 15 minutes
• Two tabs via ViewPager2: All Coins and Top Gainers

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Course Structure

Branch	Topics
main	Empty Android project scaffold
class-1	MVVM Architecture, ViewModel, LiveData, Lifecycle-aware, Retrofit, Repository Pattern
class-2	Room Database, Entities, DAOs, Paging 3, RemoteMediator
class-3	View Binding, Data Binding, Parcelable
class-4	WorkManager, ViewPager2, TabLayout
class-5	StateFlow, SharedFlow, Sealed UiState, Unidirectional Data Flow
class-6	Jetpack Compose, collectAsStateWithLifecycle

Each branch builds on the previous one. The domain and data layers are established in Class 1 and remain unchanged through Class 6 — only the UI layer evolves.

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Concepts Covered

Class 1 — MVVM Foundation

• MVVM Architecture — strict separation between Model, ViewModel, and View. Every layer communicates through interfaces, never concrete classes.
• ViewModel — survives configuration changes (rotation). Holds all UI state and business logic out of the Activity.
• LiveData — observable state holder. The Activity reacts to data changes without polling or callbacks.
• Lifecycle-aware — LiveData only delivers updates when the UI is active and automatically cleans up observers on destroy.

Class 2 — Local Persistence & Paging

• Room — SQLite abstraction. Define the schema as Kotlin data classes (@Entity), query through type-safe interfaces (@Dao).
• Entities & DAOs — CoinEntity maps to a database table; CryptoDao defines queries as suspend functions and PagingSource returns.
• Paging 3 + RemoteMediator — loads pages from the network, stores them in Room, and serves the UI from the local database. Room becomes the single source of truth.

Class 3 — Binding

• View Binding — eliminates findViewById. Every layout generates a typed binding class. No more NullPointerException from wrong IDs.
• Data Binding — the layout reads directly from the domain model (@{coin.name}). The Activity just sets binding.coin = it.
• Parcelable — pass rich domain objects across Activity boundaries. @Parcelize generates the implementation at compile time.

Class 4 — Background Work & Navigation

• WorkManager — schedules guaranteed background work. Constraints (network required), periodic intervals, and automatic retry are built in.
• ViewPager2 — swipeable tabs backed by FragmentStateAdapter. Introduces Fragments as lightweight tab hosts inside an Activity.

Class 5 — Reactive State

• StateFlow — replaces LiveData in ViewModel contracts. Cold, stateful, coroutine-native.
• SharedFlow — one-shot navigation events that must not replay on rotation.
• Sealed UiState classes — Loading, Success, Error states modeled exhaustively. when expressions in the UI are exhaustive by the compiler.

Class 6 — Jetpack Compose

• Compose — declarative UI. Composables consume the same ViewModel interfaces defined in Class 1 — the ViewModel is untouched.
• collectAsStateWithLifecycle — lifecycle-safe StateFlow collection inside Composables.
• The Class 5 → Class 6 diff is the payoff: the entire UI migration is one line per Activity and a new Composable file. The architecture layer is zero changes.

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Architecture

domain/          Pure Kotlin. Models + Repository interface. No Android imports.
data/            Retrofit, Room, mappers, repository implementation.
ui/              Activities, ViewModels, Adapters, contracts.

The ViewModel always talks to a CryptoRepository interface. The Activity always talks to a CryptoListContract interface. Concrete classes are wired up in ViewModel factories. This is what makes every class-to-class migration surgical.

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Tech Stack

Library	Version
Kotlin	2.x
Android Gradle Plugin	9.x
Retrofit + OkHttp	3.x / 5.x
Coil	2.x
Room	2.6
Paging 3	3.3
WorkManager	2.9
Jetpack Compose BOM	2024.06

API: CoinGecko Public API — free tier, no key required.