Persona MCP

# Android Kotlin Development 2025 **Updated**: 2025-11-23 | **Stack**: Kotlin, Jetpack Compose, MVVM, Coroutines --- ## Jetpack Compose UI ```kotlin // Simple Composable @Composable fun CounterScreen() { 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") } } } --- // List with LazyColumn @Composable fun TodoList(todos: List<Todo>, onToggle: (Todo) -> Unit) { LazyColumn { items(todos) { todo -> TodoItem(todo = todo, onToggle = onToggle) } } } @Composable fun TodoItem(todo: Todo, onToggle: (Todo) -> Unit) { Row( modifier = Modifier .fillMaxWidth() .clickable { onToggle(todo) } .padding(16.dp), verticalAlignment = Alignment.CenterVertically ) { Icon( imageVector = if (todo.completed) Icons.Default.CheckCircle else Icons.Default.Circle, contentDescription = null, tint = if (todo.completed) Color.Green else Color.Gray ) Spacer(modifier = Modifier.width(16.dp)) Text( text = todo.text, style = if (todo.completed) MaterialTheme.typography.bodyLarge.copy( textDecoration = TextDecoration.LineThrough ) else MaterialTheme.typography.bodyLarge ) } } --- // MVVM Architecture data class Todo( val id: String = UUID.randomUUID().toString(), val text: String, val completed: Boolean = false ) class TodoViewModel : ViewModel() { private val _todos = MutableStateFlow<List<Todo>>(emptyList()) val todos: StateFlow<List<Todo>> = _todos.asStateFlow() private val _isLoading = MutableStateFlow(false) val isLoading: StateFlow<Boolean> = _isLoading.asStateFlow() fun loadTodos() { viewModelScope.launch { _isLoading.value = true try { val result = repository.getTodos() _todos.value = result } catch (e: Exception) { // Handle error } finally { _isLoading.value = false } } } fun addTodo(text: String) { val newTodo = Todo(text = text) _todos.value = _todos.value + newTodo } fun toggleTodo(todo: Todo) { _todos.value = _todos.value.map { if (it.id == todo.id) it.copy(completed = !it.completed) else it } } } @Composable fun TodoScreen(viewModel: TodoViewModel = viewModel()) { val todos by viewModel.todos.collectAsState() val isLoading by viewModel.isLoading.collectAsState() LaunchedEffect(Unit) { viewModel.loadTodos() } if (isLoading) { Box(modifier = Modifier.fillMaxSize(), contentAlignment = Alignment.Center) { CircularProgressIndicator() } } else { TodoList(todos = todos, onToggle = viewModel::toggleTodo) } } ``` --- ## Networking (Retrofit + Coroutines) ```kotlin // API Interface interface TodoApi { @GET("todos") suspend fun getTodos(): List<Todo> @POST("todos") suspend fun createTodo(@Body todo: Todo): Todo @PUT("todos/{id}") suspend fun updateTodo(@Path("id") id: String, @Body todo: Todo): Todo @DELETE("todos/{id}") suspend fun deleteTodo(@Path("id") id: String) } // Retrofit Setup object RetrofitClient { private const val BASE_URL = "https://api.example.com/" private val okHttpClient = OkHttpClient.Builder() .addInterceptor { chain -> val request = chain.request().newBuilder() .addHeader("Authorization", "Bearer $token") .build() chain.proceed(request) } .connectTimeout(30, TimeUnit.SECONDS) .readTimeout(30, TimeUnit.SECONDS) .build() val api: TodoApi by lazy { Retrofit.Builder() .baseUrl(BASE_URL) .client(okHttpClient) .addConverterFactory(GsonConverterFactory.create()) .build() .create(TodoApi::class.java) } } // Repository class TodoRepository { private val api = RetrofitClient.api suspend fun getTodos(): Result<List<Todo>> { return try { val todos = api.getTodos() Result.success(todos) } catch (e: Exception) { Result.failure(e) } } suspend fun createTodo(text: String): Result<Todo> { return try { val todo = Todo(text = text) val created = api.createTodo(todo) Result.success(created) } catch (e: Exception) { Result.failure(e) } } } // Usage in ViewModel class TodoViewModel(private val repository: TodoRepository) : ViewModel() { fun loadTodos() { viewModelScope.launch { _isLoading.value = true repository.getTodos() .onSuccess { todos -> _todos.value = todos } .onFailure { error -> _error.value = error.message } _isLoading.value = false } } } ``` --- ## Room Database ```kotlin // Entity @Entity(tableName = "todos") data class TodoEntity( @PrimaryKey val id: String = UUID.randomUUID().toString(), val text: String, val completed: Boolean = false, val createdAt: Long = System.currentTimeMillis() ) // DAO @Dao interface TodoDao { @Query("SELECT * FROM todos ORDER BY createdAt DESC") fun getAllTodos(): Flow<List<TodoEntity>> @Query("SELECT * FROM todos WHERE id = :id") suspend fun getTodoById(id: String): TodoEntity? @Insert(onConflict = OnConflictStrategy.REPLACE) suspend fun insertTodo(todo: TodoEntity) @Update suspend fun updateTodo(todo: TodoEntity) @Delete suspend fun deleteTodo(todo: TodoEntity) @Query("DELETE FROM todos WHERE completed = 1") suspend fun deleteCompletedTodos() } // Database @Database(entities = [TodoEntity::class], version = 1, exportSchema = false) abstract class AppDatabase : RoomDatabase() { abstract fun todoDao(): TodoDao companion object { @Volatile private var INSTANCE: AppDatabase? = null fun getDatabase(context: Context): AppDatabase { return INSTANCE ?: synchronized(this) { val instance = Room.databaseBuilder( context.applicationContext, AppDatabase::class.java, "app_database" ).build() INSTANCE = instance instance } } } } // Repository class TodoRepository(private val dao: TodoDao) { val todos: Flow<List<TodoEntity>> = dao.getAllTodos() suspend fun addTodo(text: String) { val todo = TodoEntity(text = text) dao.insertTodo(todo) } suspend fun toggleTodo(todo: TodoEntity) { dao.updateTodo(todo.copy(completed = !todo.completed)) } } ``` --- ## Navigation ```kotlin // Navigation Graph @Composable fun AppNavigation() { val navController = rememberNavController() NavHost(navController = navController, startDestination = "home") { composable("home") { HomeScreen( onNavigateToDetail = { id -> navController.navigate("detail/$id") } ) } composable( route = "detail/{todoId}", arguments = listOf(navArgument("todoId") { type = NavType.StringType }) ) { backStackEntry -> val todoId = backStackEntry.arguments?.getString("todoId") DetailScreen( todoId = todoId, onNavigateBack = { navController.popBackStack() } ) } composable("settings") { SettingsScreen() } } } // Bottom Navigation @Composable fun MainScreen() { val navController = rememberNavController() Scaffold( bottomBar = { NavigationBar { NavigationBarItem( icon = { Icon(Icons.Default.Home, contentDescription = null) }, label = { Text("Home") }, selected = false, onClick = { navController.navigate("home") } ) NavigationBarItem( icon = { Icon(Icons.Default.Settings, contentDescription = null) }, label = { Text("Settings") }, selected = false, onClick = { navController.navigate("settings") } ) } } ) { paddingValues -> NavHost( navController = navController, startDestination = "home", modifier = Modifier.padding(paddingValues) ) { composable("home") { HomeScreen() } composable("settings") { SettingsScreen() } } } } ``` --- ## Dependency Injection (Hilt) ```kotlin // Application @HiltAndroidApp class MyApplication : Application() // Module @Module @InstallIn(SingletonComponent::class) object AppModule { @Provides @Singleton fun provideDatabase(@ApplicationContext context: Context): AppDatabase { return AppDatabase.getDatabase(context) } @Provides fun provideTodoDao(database: AppDatabase): TodoDao { return database.todoDao() } @Provides @Singleton fun provideRetrofit(): Retrofit { return Retrofit.Builder() .baseUrl("https://api.example.com/") .addConverterFactory(GsonConverterFactory.create()) .build() } @Provides @Singleton fun provideTodoApi(retrofit: Retrofit): TodoApi { return retrofit.create(TodoApi::class.java) } } // ViewModel with Injection @HiltViewModel class TodoViewModel @Inject constructor( private val repository: TodoRepository ) : ViewModel() { // ViewModel code } // Activity @AndroidEntryPoint class MainActivity : ComponentActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContent { MyAppTheme { AppNavigation() } } } } ``` --- ## Testing ```kotlin // Unit Test class TodoViewModelTest { private lateinit var viewModel: TodoViewModel private lateinit var repository: TodoRepository @Before fun setup() { repository = mockk() viewModel = TodoViewModel(repository) } @Test fun `addTodo adds todo to list`() = runTest { // When viewModel.addTodo("Test task") // Then val todos = viewModel.todos.value assertEquals(1, todos.size) assertEquals("Test task", todos[0].text) } @Test fun `loadTodos fetches from repository`() = runTest { // Given val mockTodos = listOf( Todo(text = "Task 1"), Todo(text = "Task 2") ) coEvery { repository.getTodos() } returns Result.success(mockTodos) // When viewModel.loadTodos() // Then advanceUntilIdle() assertEquals(mockTodos, viewModel.todos.value) coVerify { repository.getTodos() } } } --- // UI Test (Compose) @RunWith(AndroidJUnit4::class) class TodoScreenTest { @get:Rule val composeTestRule = createComposeRule() @Test fun todoList_displaysItems() { val todos = listOf( Todo(text = "Task 1", completed = false), Todo(text = "Task 2", completed = true) ) composeTestRule.setContent { TodoList(todos = todos, onToggle = {}) } // Assert composeTestRule.onNodeWithText("Task 1").assertExists() composeTestRule.onNodeWithText("Task 2").assertExists() } @Test fun clickingTodo_callsOnToggle() { var clicked = false val todo = Todo(text = "Test", completed = false) composeTestRule.setContent { TodoItem(todo = todo, onToggle = { clicked = true }) } composeTestRule.onNodeWithText("Test").performClick() assertTrue(clicked) } } ``` --- ## Google Play Submission ```markdown PREPARATION: BUILD: 1. Update version in build.gradle: versionCode 1 // Increment each release versionName "1.0.0" 2. Generate signed APK/Bundle: Build → Generate Signed Bundle/APK Create keystore (save securely!) Release build type PLAY CONSOLE: 1. Create app listing 2. App Name, Short Description (80 chars), Full Description 3. Screenshots (Phone, Tablet required) - Phone: 16:9 ratio - Tablet: Optional - Feature Graphic: 1024×500px 4. App Icon: 512×512px (high-res) 5. Content Rating (IARC questionnaire) 6. Pricing & Distribution - Free or Paid - Countries - Target Audience (age) 7. Privacy Policy URL (if app collects data) RELEASE TRACKS: - Internal Testing: Small group - Closed Testing: Specific testers - Open Testing: Public beta - Production: Live on Play Store REVIEW: - Typically 1-3 days - Faster than App Store (automated + manual) - Address issues if rejected --- PLAY STORE OPTIMIZATION (ASO): TITLE: - 50 characters - Include main keyword - "Task Manager: To-Do List App" SHORT DESCRIPTION: - 80 characters - Hook users - "Simple, powerful task management" FULL DESCRIPTION: - 4000 characters - Features, benefits - Keywords (naturally) - Formatting (bold, bullet points) SCREENSHOTS: - First 2-3 most important (shown first) - Use mockups (Device Art Generator) - Add text overlays RATINGS: - Prompt after positive experience - In-app review API (Google Play Rating) - Respond to reviews ``` --- ## Key Takeaways 1. **Jetpack Compose** - Modern UI toolkit (declarative) 2. **Kotlin Coroutines** - Async programming (simpler than RxJava) 3. **MVVM + Hilt** - Clean architecture, dependency injection 4. **Room** - Local database (type-safe SQL) 5. **Testing** - Unit + UI tests (prevent regressions) --- ## References - Android Developers Documentation - Kotlin Documentation - "Jetpack Compose by Tutorials" - raywenderlich **Related**: `jetpack-compose-advanced.md`, `kotlin-coroutines.md`, `android-testing.md`