Android架构设计Skill android-architecture

名称: android-architecture 用户可调用: false 描述: 在实现MVVM、清洁架构、使用Hilt进行依赖注入或结构化Android应用层时使用。 允许的工具:

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Android - 架构

遵循Google推荐实践的现代Android架构模式。

关键概念

MVVM 架构

模型-视图-视图模型将UI与业务逻辑分离：

// UI 状态
data class UserUiState(
    val user: User? = null,
    val isLoading: Boolean = false,
    val error: String? = null
)

// 视图模型
class UserViewModel(
    private val userRepository: UserRepository
) : ViewModel() {

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

    fun loadUser(userId: String) {
        viewModelScope.launch {
            _uiState.update { it.copy(isLoading = true, error = null) }

            userRepository.getUser(userId)
                .onSuccess { user ->
                    _uiState.update { it.copy(user = user, isLoading = false) }
                }
                .onFailure { error ->
                    _uiState.update { it.copy(error = error.message, isLoading = false) }
                }
        }
    }
}

// 可组合函数
@Composable
fun UserScreen(viewModel: UserViewModel = hiltViewModel()) {
    val uiState by viewModel.uiState.collectAsStateWithLifecycle()

    when {
        uiState.isLoading -> LoadingIndicator()
        uiState.error != null -> ErrorMessage(uiState.error!!)
        uiState.user != null -> UserContent(uiState.user!!)
    }
}

清洁架构层

app/
├── data/
│   ├── local/           # Room 数据库, DataStore
│   │   ├── dao/
│   │   └── entities/
│   ├── remote/          # Retrofit, 网络
│   │   ├── api/
│   │   └── dto/
│   └── repository/      # 存储库实现
├── domain/
│   ├── model/           # 领域模型
│   ├── repository/      # 存储库接口
│   └── usecase/         # 业务逻辑
└── presentation/
    ├── ui/              # 可组合函数
    └── viewmodel/       # 视图模型

存储库模式

// 领域层 - 接口
interface UserRepository {
    fun getUser(id: String): Flow<User>
    suspend fun saveUser(user: User): Result<Unit>
    suspend fun deleteUser(id: String): Result<Unit>
}

// 数据层 - 实现
class UserRepositoryImpl(
    private val userApi: UserApi,
    private val userDao: UserDao
) : UserRepository {

    override fun getUser(id: String): Flow<User> = flow {
        // 首先发出缓存数据
        userDao.getUser(id)?.let { emit(it.toDomain()) }

        // 获取新数据
        try {
            val remoteUser = userApi.getUser(id)
            userDao.insertUser(remoteUser.toEntity())
            emit(remoteUser.toDomain())
        } catch (e: Exception) {
            // 网络错误，缓存数据已发出
        }
    }

    override suspend fun saveUser(user: User): Result<Unit> = runCatching {
        userApi.updateUser(user.toDto())
        userDao.insertUser(user.toEntity())
    }
}

最佳实践

使用Hilt进行依赖注入

// 模块定义
@Module
@InstallIn(SingletonComponent::class)
object NetworkModule {

    @Provides
    @Singleton
    fun provideRetrofit(): Retrofit {
        return Retrofit.Builder()
            .baseUrl(BuildConfig.API_BASE_URL)
            .addConverterFactory(MoshiConverterFactory.create())
            .build()
    }

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

@Module
@InstallIn(SingletonComponent::class)
abstract class RepositoryModule {

    @Binds
    @Singleton
    abstract fun bindUserRepository(impl: UserRepositoryImpl): UserRepository
}

// 视图模型注入
@HiltViewModel
class UserViewModel @Inject constructor(
    private val getUserUseCase: GetUserUseCase,
    private val savedStateHandle: SavedStateHandle
) : ViewModel() {

    private val userId: String = savedStateHandle.get<String>("userId")
        ?: throw IllegalArgumentException("userId required")

    // 视图模型实现
}

业务逻辑用例

class GetUserUseCase @Inject constructor(
    private val userRepository: UserRepository,
    private val analyticsTracker: AnalyticsTracker
) {
    operator fun invoke(userId: String): Flow<Result<User>> = flow {
        emit(Result.Loading)

        userRepository.getUser(userId)
            .catch { e ->
                analyticsTracker.trackError("get_user_failed", e)
                emit(Result.Error(e))
            }
            .collect { user ->
                emit(Result.Success(user))
            }
    }
}

// 结果的密封类
sealed class Result<out T> {
    data class Success<T>(val data: T) : Result<T>()
    data class Error(val exception: Throwable) : Result<Nothing>()
    object Loading : Result<Nothing>()
}

Room 数据库设置

@Entity(tableName = "users")
data class UserEntity(
    @PrimaryKey val id: String,
    val name: String,
    val email: String,
    @ColumnInfo(name = "created_at") val createdAt: Long
)

@Dao
interface UserDao {
    @Query("SELECT * FROM users WHERE id = :id")
    suspend fun getUser(id: String): UserEntity?

    @Query("SELECT * FROM users ORDER BY name ASC")
    fun getAllUsers(): Flow<List<UserEntity>>

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    suspend fun insertUser(user: UserEntity)

    @Delete
    suspend fun deleteUser(user: UserEntity)
}

@Database(entities = [UserEntity::class], version = 1)
abstract class AppDatabase : RoomDatabase() {
    abstract fun userDao(): UserDao
}

// Hilt 模块
@Module
@InstallIn(SingletonComponent::class)
object DatabaseModule {

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

    @Provides
    fun provideUserDao(database: AppDatabase): UserDao {
        return database.userDao()
    }
}

数据映射

// DTO（数据传输对象）- 来自API
data class UserDto(
    @Json(name = "id") val id: String,
    @Json(name = "full_name") val fullName: String,
    @Json(name = "email_address") val email: String
)

// 实体 - 用于Room
@Entity(tableName = "users")
data class UserEntity(
    @PrimaryKey val id: String,
    val name: String,
    val email: String
)

// 领域模型
data class User(
    val id: String,
    val name: String,
    val email: String
)

// 映射器
fun UserDto.toEntity() = UserEntity(
    id = id,
    name = fullName,
    email = email
)

fun UserDto.toDomain() = User(
    id = id,
    name = fullName,
    email = email
)

fun UserEntity.toDomain() = User(
    id = id,
    name = name,
    email = email
)

fun User.toEntity() = UserEntity(
    id = id,
    name = name,
    email = email
)

常见模式

单一数据源

class OfflineFirstRepository @Inject constructor(
    private val api: ItemApi,
    private val dao: ItemDao
) : ItemRepository {

    override fun getItems(): Flow<List<Item>> {
        return dao.getAllItems()
            .map { entities -> entities.map { it.toDomain() } }
            .onStart {
                // 在后台从网络刷新
                refreshItems()
            }
    }

    private suspend fun refreshItems() {
        try {
            val remoteItems = api.getItems()
            dao.deleteAll()
            dao.insertAll(remoteItems.map { it.toEntity() })
        } catch (e: Exception) {
            // 记录错误，本地数据仍可用
        }
    }
}

类型安全导航参数

// 定义路由
sealed class Screen(val route: String) {
    object Home : Screen("home")
    object Detail : Screen("detail/{itemId}") {
        fun createRoute(itemId: String) = "detail/$itemId"
    }
    object Settings : Screen("settings")
}

// 导航设置
@Composable
fun AppNavigation(navController: NavHostController) {
    NavHost(navController = navController, startDestination = Screen.Home.route) {
        composable(Screen.Home.route) {
            HomeScreen(
                onItemClick = { itemId ->
                    navController.navigate(Screen.Detail.createRoute(itemId))
                }
            )
        }
        composable(
            route = Screen.Detail.route,
            arguments = listOf(navArgument("itemId") { type = NavType.StringType })
        ) { backStackEntry ->
            DetailScreen(
                itemId = backStackEntry.arguments?.getString("itemId") ?: return@composable
            )
        }
    }
}

错误处理

sealed class UiState<out T> {
    object Loading : UiState<Nothing>()
    data class Success<T>(val data: T) : UiState<T>()
    data class Error(val message: String, val retry: (() -> Unit)? = null) : UiState<Nothing>()
}

@Composable
fun <T> StateHandler(
    state: UiState<T>,
    onRetry: () -> Unit = {},
    content: @Composable (T) -> Unit
) {
    when (state) {
        is UiState.Loading -> {
            Box(modifier = Modifier.fillMaxSize(), contentAlignment = Alignment.Center) {
                CircularProgressIndicator()
            }
        }
        is UiState.Error -> {
            Column(
                modifier = Modifier.fillMaxSize(),
                horizontalAlignment = Alignment.CenterHorizontally,
                verticalArrangement = Arrangement.Center
            ) {
                Text(state.message)
                Spacer(modifier = Modifier.height(16.dp))
                Button(onClick = onRetry) {
                    Text("重试")
                }
            }
        }
        is UiState.Success -> content(state.data)
    }
}

反模式

上帝Activity/Fragment

坏：所有逻辑在一个Activity中。

好：使用MVVM，职责清晰分离。

在ViewModel中进行网络调用

坏：

class BadViewModel : ViewModel() {
    fun loadData() {
        val client = OkHttpClient()  // 直接网络依赖
        // ...
    }
}

好：通过构造函数注入存储库。

暴露可变状态

坏：

class BadViewModel : ViewModel() {
    val uiState = MutableStateFlow(UiState())  // 可变暴露！
}

好：

class GoodViewModel : ViewModel() {
    private val _uiState = MutableStateFlow(UiState())
    val uiState: StateFlow<UiState> = _uiState.asStateFlow()
}

相关技能

• android-jetpack-compose: UI层模式
• android-kotlin-coroutines: 异步操作