Android Development

Comprehensive guide for building modern Android applications.

Platforms Covered

Platform	Min SDK	Target SDK
Android Phone	API 24 (7.0)	API 34 (14)
Android Tablet	API 24	API 34
Android TV	API 24	API 34
Wear OS	API 30	API 34
Android Auto	API 29	API 34

---

Jetpack Compose (Modern UI)

Basic Structure

@Composable
fun MyApp() {
    MaterialTheme {
        Surface(
            modifier = Modifier.fillMaxSize(),
            color = MaterialTheme.colorScheme.background
        ) {
            MainScreen()
        }
    }
}

@Composable
fun MainScreen() {
    var count by remember { mutableStateOf(0) }

    Column(
        modifier = Modifier
            .fillMaxSize()
            .padding(16.dp),
        horizontalAlignment = Alignment.CenterHorizontally,
        verticalArrangement = Arrangement.Center
    ) {
        Text(
            text = "Count: $count",
            style = MaterialTheme.typography.headlineLarge
        )

        Spacer(modifier = Modifier.height(16.dp))

        Button(onClick = { count++ }) {
            Text("Increment")
        }
    }
}

State Management

// Local state
var text by remember { mutableStateOf("") }

// State hoisting
@Composable
fun StatefulCounter() {
    var count by remember { mutableStateOf(0) }
    StatelessCounter(count = count, onIncrement = { count++ })
}

@Composable
fun StatelessCounter(count: Int, onIncrement: () -> Unit) {
    Button(onClick = onIncrement) {
        Text("Count: $count")
    }
}

// ViewModel state
@HiltViewModel
class MainViewModel @Inject constructor(
    private val repository: ItemRepository
) : ViewModel() {

    private val _uiState = MutableStateFlow(UiState())
    val uiState: StateFlow<UiState> = _uiState.asStateFlow()

    fun loadItems() {
        viewModelScope.launch {
            _uiState.update { it.copy(isLoading = true) }
            try {
                val items = repository.getItems()
                _uiState.update { it.copy(items = items, isLoading = false) }
            } catch (e: Exception) {
                _uiState.update { it.copy(error = e.message, isLoading = false) }
            }
        }
    }
}

// Collecting in Compose
@Composable
fun MainScreen(viewModel: MainViewModel = hiltViewModel()) {
    val uiState by viewModel.uiState.collectAsStateWithLifecycle()

    when {
        uiState.isLoading -> LoadingIndicator()
        uiState.error != null -> ErrorMessage(uiState.error!!)
        else -> ItemList(uiState.items)
    }
}

Navigation

// Navigation setup
@Composable
fun AppNavigation() {
    val navController = rememberNavController()

    NavHost(navController = navController, startDestination = "home") {
        composable("home") {
            HomeScreen(
                onNavigateToDetail = { id ->
                    navController.navigate("detail/$id")
                }
            )
        }
        composable(
            route = "detail/{itemId}",
            arguments = listOf(navArgument("itemId") { type = NavType.StringType })
        ) { backStackEntry ->
            val itemId = backStackEntry.arguments?.getString("itemId")
            DetailScreen(itemId = itemId)
        }
    }
}

// Type-safe navigation (recommended)
@Serializable
data class DetailRoute(val itemId: String)

navController.navigate(DetailRoute(itemId = "123"))

Lists

@Composable
fun ItemList(items: List<Item>) {
    LazyColumn(
        modifier = Modifier.fillMaxSize(),
        contentPadding = PaddingValues(16.dp),
        verticalArrangement = Arrangement.spacedBy(8.dp)
    ) {
        items(
            items = items,
            key = { it.id }
        ) { item ->
            ItemCard(item = item)
        }
    }
}

// Pull to refresh
@OptIn(ExperimentalMaterial3Api::class)
@Composable
fun RefreshableList(
    items: List<Item>,
    isRefreshing: Boolean,
    onRefresh: () -> Unit
) {
    val pullRefreshState = rememberPullToRefreshState()

    PullToRefreshBox(
        isRefreshing = isRefreshing,
        onRefresh = onRefresh,
        state = pullRefreshState
    ) {
        LazyColumn { /* content */ }
    }
}

---

Modern Android Architecture

Clean Architecture Layers

app/
├── data/
│   ├── local/
│   │   ├── AppDatabase.kt
│   │   └── ItemDao.kt
│   ├── remote/
│   │   ├── ApiService.kt
│   │   └── ItemDto.kt
│   └── repository/
│       └── ItemRepositoryImpl.kt
├── domain/
│   ├── model/
│   │   └── Item.kt
│   ├── repository/
│   │   └── ItemRepository.kt
│   └── usecase/
│       └── GetItemsUseCase.kt
├── presentation/
│   ├── home/
│   │   ├── HomeScreen.kt
│   │   └── HomeViewModel.kt
│   └── navigation/
│       └── AppNavigation.kt
└── di/
    └── AppModule.kt

Dependency Injection (Hilt)

@HiltAndroidApp
class MyApplication : Application()

@Module
@InstallIn(SingletonComponent::class)
object AppModule {

    @Provides
    @Singleton
    fun provideDatabase(@ApplicationContext context: Context): AppDatabase {
        return Room.databaseBuilder(
            context,
            AppDatabase::class.java,
            "app_database"
        ).build()
    }

    @Provides
    @Singleton
    fun provideApiService(): ApiService {
        return Retrofit.Builder()
            .baseUrl("https://api.example.com/")
            .addConverterFactory(GsonConverterFactory.create())
            .build()
            .create(ApiService::class.java)
    }

    @Provides
    @Singleton
    fun provideItemRepository(
        apiService: ApiService,
        database: AppDatabase
    ): ItemRepository {
        return ItemRepositoryImpl(apiService, database.itemDao())
    }
}

---

Data Layer

Room Database

@Entity(tableName = "items")
data class ItemEntity(
    @PrimaryKey val id: String,
    val name: String,
    val createdAt: Long
)

@Dao
interface ItemDao {
    @Query("SELECT * FROM items ORDER BY createdAt DESC")
    fun getItems(): Flow<List<ItemEntity>>

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    suspend fun insertItems(items: List<ItemEntity>)

    @Delete
    suspend fun deleteItem(item: ItemEntity)
}

@Database(entities = [ItemEntity::class], version = 1)
abstract class AppDatabase : RoomDatabase() {
    abstract fun itemDao(): ItemDao
}

Retrofit API

interface ApiService {
    @GET("items")
    suspend fun getItems(): List<ItemDto>

    @POST("items")
    suspend fun createItem(@Body item: CreateItemRequest): ItemDto

    @DELETE("items/{id}")
    suspend fun deleteItem(@Path("id") id: String)
}

data class ItemDto(
    val id: String,
    val name: String,
    @SerializedName("created_at") val createdAt: String
)

Repository Pattern

interface ItemRepository {
    fun getItems(): Flow<List<Item>>
    suspend fun refreshItems()
    suspend fun deleteItem(id: String)
}

class ItemRepositoryImpl @Inject constructor(
    private val apiService: ApiService,
    private val itemDao: ItemDao
) : ItemRepository {

    override fun getItems(): Flow<List<Item>> {
        return itemDao.getItems().map { entities ->
            entities.map { it.toDomain() }
        }
    }

    override suspend fun refreshItems() {
        val items = apiService.getItems()
        itemDao.insertItems(items.map { it.toEntity() })
    }
}

---

Material Design 3

Theme Setup

@Composable
fun MyAppTheme(
    darkTheme: Boolean = isSystemInDarkTheme(),
    dynamicColor: Boolean = true,
    content: @Composable () -> Unit
) {
    val colorScheme = when {
        dynamicColor && Build.VERSION.SDK_INT >= Build.VERSION_CODES.S -> {
            val context = LocalContext.current
            if (darkTheme) dynamicDarkColorScheme(context)
            else dynamicLightColorScheme(context)
        }
        darkTheme -> DarkColorScheme
        else -> LightColorScheme
    }

    MaterialTheme(
        colorScheme = colorScheme,
        typography = Typography,
        content = content
    )
}

Common Components

// Top App Bar
@OptIn(ExperimentalMaterial3Api::class)
@Composable
fun MyTopBar(
    title: String,
    onBackClick: () -> Unit
) {
    TopAppBar(
        title = { Text(title) },
        navigationIcon = {
            IconButton(onClick = onBackClick) {
                Icon(Icons.Default.ArrowBack, contentDescription = "Back")
            }
        },
        actions = {
            IconButton(onClick = { /* menu */ }) {
                Icon(Icons.Default.MoreVert, contentDescription = "Menu")
            }
        }
    )
}

// Bottom Navigation
@Composable
fun MyBottomBar(
    selectedTab: Int,
    onTabSelected: (Int) -> Unit
) {
    NavigationBar {
        NavigationBarItem(
            icon = { Icon(Icons.Default.Home, contentDescription = null) },
            label = { Text("Home") },
            selected = selectedTab == 0,
            onClick = { onTabSelected(0) }
        )
        NavigationBarItem(
            icon = { Icon(Icons.Default.Settings, contentDescription = null) },
            label = { Text("Settings") },
            selected = selectedTab == 1,
            onClick = { onTabSelected(1) }
        )
    }
}

---

Platform-Specific

Android TV

// Focus management
@Composable
fun TvButton(
    onClick: () -> Unit,
    content: @Composable () -> Unit
) {
    var isFocused by remember { mutableStateOf(false) }

    Box(
        modifier = Modifier
            .onFocusChanged { isFocused = it.isFocused }
            .focusable()
            .clickable(onClick = onClick)
            .background(
                if (isFocused) MaterialTheme.colorScheme.primary
                else MaterialTheme.colorScheme.surface
            )
    ) {
        content()
    }
}

Wear OS

@Composable
fun WearApp() {
    MaterialTheme {
        ScalingLazyColumn(
            modifier = Modifier.fillMaxSize(),
            anchorType = ScalingLazyListAnchorType.ItemCenter
        ) {
            item { TimeText() }
            item {
                Chip(
                    onClick = { },
                    label = { Text("Action") }
                )
            }
        }
    }
}

---

Testing

Unit Tests

@Test
fun `getItems returns mapped domain objects`() = runTest {
    val repository = ItemRepositoryImpl(
        apiService = FakeApiService(),
        itemDao = FakeItemDao()
    )

    val items = repository.getItems().first()

    assertEquals(2, items.size)
    assertEquals("Item 1", items[0].name)
}

Compose UI Tests

@HiltAndroidTest
class MainScreenTest {
    @get:Rule
    val composeTestRule = createAndroidComposeRule<MainActivity>()

    @Test
    fun displayItems_whenLoaded() {
        composeTestRule.onNodeWithText("Item 1").assertIsDisplayed()
        composeTestRule.onNodeWithText("Item 2").assertIsDisplayed()
    }

    @Test
    fun navigateToDetail_onItemClick() {
        composeTestRule.onNodeWithText("Item 1").performClick()
        composeTestRule.onNodeWithText("Item Details").assertIsDisplayed()
    }
}

---

Play Store Requirements

Required

• Privacy policy
• App icon (512x512)
• Feature graphic (1024x500)
• Screenshots (min 2)
• Target API 34+

App Bundle

android {
    bundle {
        language {
            enableSplit = true
        }
        density {
            enableSplit = true
        }
        abi {
            enableSplit = true
        }
    }
}

---

Best Practices

DO:

• Use Kotlin Coroutines and Flow
• Follow unidirectional data flow
• Use Jetpack Compose for new UI
• Implement proper lifecycle handling
• Support multiple screen sizes

DON'T:

• Block main thread
• Leak contexts
• Hardcode dimensions
• Ignore process death
• Skip ProGuard rules

---

Kotlin Multiplatform (KMP) / Compose Multiplatform (CMP)

Shared Business Logic with KMP

// shared/src/commonMain/kotlin/UserRepository.kt
expect class PlatformContext

class UserRepository(private val api: ApiService, private val db: Database) {
    suspend fun getUsers(): List<User> {
        return try {
            val remote = api.fetchUsers()
            db.saveUsers(remote)
            remote
        } catch (e: Exception) {
            db.getCachedUsers()
        }
    }
}

// shared/src/androidMain/kotlin/PlatformContext.kt
actual class PlatformContext(val context: Context)

// shared/src/iosMain/kotlin/PlatformContext.kt
actual class PlatformContext

Compose Multiplatform (Shared UI)

// shared/src/commonMain/kotlin/App.kt
@Composable
fun App() {
    MaterialTheme {
        var users by remember { mutableStateOf<List<User>>(emptyList()) }
        val repository = remember { UserRepository() }

        LaunchedEffect(Unit) {
            users = repository.getUsers()
        }

        LazyColumn {
            items(users) { user ->
                UserCard(user)
            }
        }
    }
}

// Runs natively on Android, iOS, Desktop, and Web

KMP Project Structure

project/
├── shared/
│   └── src/
│       ├── commonMain/     # Shared Kotlin code
│       ├── androidMain/    # Android-specific
│       ├── iosMain/        # iOS-specific
│       └── desktopMain/    # Desktop-specific
├── androidApp/             # Android entry point
├── iosApp/                 # iOS entry point (Swift/SwiftUI)
└── desktopApp/             # Desktop entry point

---

Navigation 3 (Type-Safe Navigation)

// Define routes as serializable data classes
@Serializable
data object Home

@Serializable
data class Detail(val itemId: String)

@Serializable
data class Settings(val section: String? = null)

// Navigation setup
@Composable
fun AppNavHost(navController: NavHostController = rememberNavController()) {
    NavHost(navController = navController, startDestination = Home) {
        composable<Home> {
            HomeScreen(onItemClick = { id ->
                navController.navigate(Detail(itemId = id))
            })
        }
        composable<Detail> { backStackEntry ->
            val detail: Detail = backStackEntry.toRoute()
            DetailScreen(itemId = detail.itemId)
        }
        composable<Settings> { backStackEntry ->
            val settings: Settings = backStackEntry.toRoute()
            SettingsScreen(section = settings.section)
        }
    }
}

---

API 35 (Android 15) Features

Feature	Description
Edge-to-edge enforced	Apps must handle insets properly
Predictive back	System back gesture with preview animations
Private Space	User-controlled hidden app profile
Satellite connectivity	SMS/MMS over satellite
App archival	Auto-archive unused apps, preserve data
Health Connect	Updated health data APIs

// Edge-to-edge (required on API 35+)
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    enableEdgeToEdge()

    setContent {
        Scaffold(
            modifier = Modifier.fillMaxSize(),
            contentWindowInsets = ScaffoldDefaults.contentWindowInsets,
        ) { innerPadding ->
            MainContent(modifier = Modifier.padding(innerPadding))
        }
    }
}

// Predictive back with Compose
@OptIn(ExperimentalMaterial3Api::class)
@Composable
fun DetailScreen(onBack: () -> Unit) {
    BackHandler(onBack = onBack)
    // Content renders with predictive back animation automatically
}

---

Baseline Profiles for Startup Performance

// baselineprofile/build.gradle.kts
dependencies {
    implementation("androidx.benchmark:benchmark-macro-junit4:1.3.0")
}

// BaselineProfileGenerator.kt
@RunWith(AndroidJUnit4::class)
class BaselineProfileGenerator {
    @get:Rule
    val rule = BaselineProfileRule()

    @Test
    fun generateBaselineProfile() {
        rule.collect(packageName = "com.example.app") {
            // Critical user journey
            pressHome()
            startActivityAndWait()
            device.findObject(By.text("Login")).click()
            device.wait(Until.hasObject(By.text("Dashboard")), 5000)
        }
    }
}

// app/build.gradle.kts
android {
    buildTypes {
        release {
            // Baseline profiles improve startup by 15-30%
            baselineProfile.automaticGenerationDuringBuild = true
        }
    }
}

---

Credential Manager API

// Modern sign-in replacing legacy APIs
val credentialManager = CredentialManager.create(context)

// Sign in with passkeys, passwords, or federated identity
suspend fun signIn() {
    val request = GetCredentialRequest(listOf(
        GetPasswordOption(),
        GetPublicKeyCredentialOption(requestJson = passkeyRequestJson),
        GetGoogleIdOption(serverClientId = WEB_CLIENT_ID),
    ))

    try {
        val result = credentialManager.getCredential(context, request)
        handleSignIn(result)
    } catch (e: GetCredentialException) {
        handleSignInError(e)
    }
}

// Create a passkey
suspend fun createPasskey() {
    val request = CreatePublicKeyCredentialRequest(
        requestJson = createPasskeyRequestJson
    )
    val result = credentialManager.createCredential(context, request)
    handlePasskeyCreation(result)
}