name: android-kotlin-development description: Develop native Android apps with Kotlin. Covers MVVM with Jetpack, Compose for modern UI, Retrofit for API calls, Room for local storage, and navigation architecture.

Android Kotlin Development

Overview

Build robust native Android applications using Kotlin with modern architecture patterns, Jetpack libraries, and Compose for declarative UI.

When to Use

• Creating native Android applications with best practices
• Using Kotlin for type-safe development
• Implementing MVVM architecture with Jetpack
• Building modern UIs with Jetpack Compose
• Integrating with Android platform APIs

Instructions

1. Models & API Service

// Models
data class User(
  val id: String,
  val name: String,
  val email: String,
  val avatarUrl: String? = null
)

data class Item(
  val id: String,
  val title: String,
  val description: String,
  val imageUrl: String? = null,
  val price: Double
)

// API Service with Retrofit
interface ApiService {
  @GET("/users/{id}")
  suspend fun getUser(@Path("id") userId: String): User

  @PUT("/users/{id}")
  suspend fun updateUser(
    @Path("id") userId: String,
    @Body user: User
  ): User

  @GET("/items")
  suspend fun getItems(@Query("filter") filter: String = "all"): List<Item>

  @POST("/items")
  suspend fun createItem(@Body item: Item): Item
}

// Network client setup
@Module
@InstallIn(SingletonComponent::class)
object NetworkModule {
  @Provides
  @Singleton
  fun provideRetrofit(): Retrofit {
    val httpClient = OkHttpClient.Builder()
      .addInterceptor { chain ->
        val original = chain.request()
        val requestBuilder = original.newBuilder()

        val token = PreferencesManager.getToken()
        if (token.isNotEmpty()) {
          requestBuilder.addHeader("Authorization", "Bearer $token")
        }

        requestBuilder.addHeader("Content-Type", "application/json")
        chain.proceed(requestBuilder.build())
      }
      .connectTimeout(30, TimeUnit.SECONDS)
      .readTimeout(30, TimeUnit.SECONDS)
      .build()

    return Retrofit.Builder()
      .baseUrl("https://api.example.com")
      .client(httpClient)
      .addConverterFactory(GsonConverterFactory.create())
      .build()
  }

  @Provides
  @Singleton
  fun provideApiService(retrofit: Retrofit): ApiService {
    return retrofit.create(ApiService::class.java)
  }
}

2. MVVM ViewModels with Jetpack

@HiltViewModel
class UserViewModel @Inject constructor(
  private val apiService: ApiService
) : ViewModel() {
  private val _user = MutableStateFlow<User?>(null)
  val user: StateFlow<User?> = _user.asStateFlow()

  private val _isLoading = MutableStateFlow(false)
  val isLoading: StateFlow<Boolean> = _isLoading.asStateFlow()

  private val _errorMessage = MutableStateFlow<String?>(null)
  val errorMessage: StateFlow<String?> = _errorMessage.asStateFlow()

  fun fetchUser(userId: String) {
    viewModelScope.launch {
      _isLoading.value = true
      _errorMessage.value = null

      try {
        val user = apiService.getUser(userId)
        _user.value = user
      } catch (e: Exception) {
        _errorMessage.value = e.message ?: "Unknown error"
      } finally {
        _isLoading.value = false
      }
    }
  }

  fun logout() {
    _user.value = null
  }
}

@HiltViewModel
class ItemsViewModel @Inject constructor(
  private val apiService: ApiService
) : ViewModel() {
  private val _items = MutableStateFlow<List<Item>>(emptyList())
  val items: StateFlow<List<Item>> = _items.asStateFlow()

  private val _isLoading = MutableStateFlow(false)
  val isLoading: StateFlow<Boolean> = _isLoading.asStateFlow()

  fun fetchItems(filter: String = "all") {
    viewModelScope.launch {
      _isLoading.value = true
      try {
        val items = apiService.getItems(filter)
        _items.value = items
      } catch (e: Exception) {
        println("Error fetching items: ${e.message}")
      } finally {
        _isLoading.value = false
      }
    }
  }

  fun addItem(item: Item) {
    viewModelScope.launch {
      try {
        val created = apiService.createItem(item)
        _items.value = _items.value + created
      } catch (e: Exception) {
        println("Error creating item: ${e.message}")
      }
    }
  }
}

3. Jetpack Compose UI

@Composable
fun MainScreen() {
  val navController = rememberNavController()

  NavHost(navController = navController, startDestination = "home") {
    composable("home") { HomeScreen(navController) }
    composable("profile") { ProfileScreen(navController) }
    composable("details/{itemId}") { backStackEntry ->
      val itemId = backStackEntry.arguments?.getString("itemId") ?: return@composable
      DetailsScreen(itemId = itemId, navController = navController)
    }
  }
}

@Composable
fun HomeScreen(navController: NavController) {
  val viewModel: ItemsViewModel = hiltViewModel()
  val items by viewModel.items.collectAsState()
  val isLoading by viewModel.isLoading.collectAsState()

  LaunchedEffect(Unit) {
    viewModel.fetchItems()
  }

  Scaffold(
    topBar = { TopAppBar(title = { Text("Items") }) }
  ) { paddingValues ->
    if (isLoading) {
      Box(modifier = Modifier.fillMaxSize(), contentAlignment = Alignment.Center) {
        CircularProgressIndicator()
      }
    } else {
      LazyColumn(
        modifier = Modifier
          .padding(paddingValues)
          .fillMaxSize(),
        contentPadding = PaddingValues(8.dp)
      ) {
        items(items) { item ->
          ItemCard(
            item = item,
            onClick = { navController.navigate("details/${item.id}") }
          )
        }
      }
    }
  }
}

@Composable
fun ItemCard(item: Item, onClick: () -> Unit) {
  Card(
    modifier = Modifier
      .fillMaxWidth()
      .padding(8.dp)
      .clickable { onClick() }
  ) {
    Row(modifier = Modifier.padding(16.dp)) {
      Column(modifier = Modifier.weight(1f)) {
        Text(text = item.title, style = MaterialTheme.typography.headlineSmall)
        Text(text = item.description, style = MaterialTheme.typography.bodyMedium)
        Text(text = "$${item.price}", style = MaterialTheme.typography.bodySmall)
      }
      Icon(imageVector = Icons.Default.ArrowForward, contentDescription = null)
    }
  }
}

@Composable
fun ProfileScreen(navController: NavController) {
  val viewModel: UserViewModel = hiltViewModel()
  val user by viewModel.user.collectAsState()
  val isLoading by viewModel.isLoading.collectAsState()

  LaunchedEffect(Unit) {
    viewModel.fetchUser("current-user")
  }

  Scaffold(
    topBar = { TopAppBar(title = { Text("Profile") }) }
  ) { paddingValues ->
    if (isLoading) {
      Box(modifier = Modifier.fillMaxSize(), contentAlignment = Alignment.Center) {
        CircularProgressIndicator()
      }
    } else if (user != null) {
      Column(
        modifier = Modifier
          .padding(paddingValues)
          .fillMaxSize()
          .padding(16.dp)
      ) {
        Text(text = user!!.name, style = MaterialTheme.typography.headlineMedium)
        Text(text = user!!.email, style = MaterialTheme.typography.bodyMedium)

        Spacer(modifier = Modifier.height(24.dp))

        Button(
          onClick = { viewModel.logout() },
          modifier = Modifier.fillMaxWidth()
        ) {
          Text("Logout")
        }
      }
    }
  }
}

@Composable
fun DetailsScreen(itemId: String, navController: NavController) {
  Scaffold(
    topBar = {
      TopAppBar(
        title = { Text("Details") },
        navigationIcon = {
          IconButton(onClick = { navController.popBackStack() }) {
            Icon(Icons.Default.ArrowBack, contentDescription = "Back")
          }
        }
      )
    }
  ) { paddingValues ->
    Column(
      modifier = Modifier
        .padding(paddingValues)
        .fillMaxSize()
        .padding(16.dp),
      horizontalAlignment = Alignment.CenterHorizontally,
      verticalArrangement = Arrangement.Center
    ) {
      Text("Item ID: $itemId", style = MaterialTheme.typography.headlineSmall)
    }
  }
}

Best Practices

✅ DO

• Use Kotlin for all new Android code
• Implement MVVM with Jetpack libraries
• Use Jetpack Compose for UI development
• Leverage coroutines for async operations
• Use Room for local data persistence
• Implement proper error handling
• Use Hilt for dependency injection
• Use StateFlow for reactive state
• Test on multiple device types
• Follow Android design guidelines

❌ DON'T

• Store tokens in SharedPreferences
• Make network calls on main thread
• Ignore lifecycle management
• Skip null safety checks
• Hardcode strings and resources
• Ignore configuration changes
• Store passwords in code
• Deploy without device testing
• Use deprecated APIs
• Accumulate memory leaks