Android：什么是它、系统架构和Kotlin开发

// 通过AIDL接口使用Binder工作的示例
interface IDataService : android.os.IInterface {
    fun getData(): List<DataItem>
    fun saveData(item: DataItem): Boolean
}

// 服务实现
class DataService : Service() {
    private val binder = object : IDataService.Stub() {
        override fun getData(): List<DataItem> = repository.getAll()
        override fun saveData(item: DataItem): Boolean = repository.save(item)
    }

    override fun onBind(intent: Intent?): IBinder = binder
}

// 使用协程和Flow的Kotlin代码示例
data class User(
    val id: Long,
    val name: String,
    val email: String
)

class UserRepository(
    private val api: UserApi,
    private val dao: UserDao
) {
    suspend fun getUser(id: Long): Result<User> {
        return try {
            val cached = dao.getUser(id)
            if (cached != null) {
                return Result.success(cached)
            }
            val remote = api.fetchUser(id)
            dao.insertUser(remote)
            Result.success(remote)
        } catch (e: Exception) {
            Result.failure(e)
        }
    }

    fun observeUsers(): Flow<List<User>> {
        return dao.observeAll()
            .map { list -> list.sortedBy { it.name } }
            .flowOn(Dispatchers.Default)
    }
}

// 使用协程和StateFlow的ViewModel
class UserViewModel(
    private val repository: UserRepository
) : ViewModel() {

    private val _users = MutableStateFlow<List<User>>(emptyList())
    val users: StateFlow<List<User>> = _users.asStateFlow()

    private val _loading = MutableStateFlow(false)
    val loading: StateFlow<Boolean> = _loading.asStateFlow()

    init {
        viewModelScope.launch {
            repository.observeUsers().collect { userList ->
                _users.value = userList
            }
        }
    }

    fun refresh() {
        viewModelScope.launch {
            _loading.value = true
            repository.getUser(42).onSuccess { user ->
                _users.value = listOf(user)
            }
            _loading.value = false
        }
    }
}

// Jetpack Compose — 用户资料屏幕
@Composable
fun ProfileScreen(
    user: User,
    onEditClick: () -> Unit,
    modifier: Modifier = Modifier
) {
    Column(
        modifier = modifier
            .fillMaxSize()
            .padding(16.dp),
        horizontalAlignment = Alignment.CenterHorizontally
    ) {
        AsyncImage(
            model = user.avatarUrl,
            contentDescription = "用户头像",
            modifier = Modifier
                .size(120.dp)
                .clip(CircleShape)
        )

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

        Text(
            text = user.name,
            style = MaterialTheme.typography.headlineMedium
        )

        Text(
            text = user.email,
            style = MaterialTheme.typography.bodyLarge,
            color = MaterialTheme.colorScheme.onSurfaceVariant
        )

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

        Button(onClick = onEditClick) {
            Icon(Icons.Default.Edit, contentDescription = null)
            Spacer(modifier = Modifier.width(8.dp))
            Text("编辑个人资料")
        }
    }
}

@Preview(showBackground = true, showSystemUi = true)
@Composable
fun ProfileScreenPreview() {
    MaterialTheme {
        ProfileScreen(
            user = User(1, "安娜·彼得罗娃", "anna@example.com"),
            onEditClick = {}
        )
    }
}

// 通过LifecycleScope处理生命周期的Activity
class MainActivity : ComponentActivity() {
    private val viewModel: UserViewModel by viewModels()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        setContent {
            MaterialTheme {
                lifecycleScope.launch {
                    repeatOnLifecycle(Lifecycle.State.STARTED) {
                        viewModel.users.collect { users ->
                            updateUi(users)
                        }
                    }
                }
            }
        }
    }

    override fun onSaveInstanceState(outState: Bundle) {
        super.onSaveInstanceState(outState)
        outState.putString("last_search", searchQuery)
    }

    override fun onRestoreInstanceState(savedInstanceState: Bundle) {
        super.onRestoreInstanceState(savedInstanceState)
        searchQuery = savedInstanceState.getString("last_search", "")
    }
}