Network + cache with a single source of truth.
// NetworkBoundResource.kt (simplified)
suspend fun <T> networkBoundResource(
query: suspend () -> T?,
fetch: suspend () -> T,
saveFetchResult: suspend (T) -> Unit,
): T {
val cached = query()
return if (cached != null) cached else fetch().also { saveFetchResult(it) }
}
// TodosRepoImpl.kt
class TodosRepoImpl @Inject constructor(
private val api: Api,
private val dao: TodoDao,
) : TodosRepo {
override suspend fun list(): List<String> = networkBoundResource(
query = { dao.getAll()?.map { it.title } },
fetch = { api.getTodos().map { it.name } },
saveFetchResult = { items -> dao.insertAll(items.map { TodoEntity(title = it) }) },
)
}
Retrofit API + Room DAO + Repository + Compose UI.
// data/Api.kt
interface Api { @GET("/todos") suspend fun getTodos(): List<TodoDto> }
data class TodoDto(val id: String, val name: String)
// data/db/TodoEntity.kt
@Entity tableName = "todos"
data class TodoEntity(@PrimaryKey val id: String, val title: String)
@Dao interface TodoDao {
@Query("SELECT * FROM todos") suspend fun getAll(): List<TodoEntity>
@Insert(onConflict = OnConflictStrategy.REPLACE) suspend fun insertAll(items: List<TodoEntity>)
}
// data/TodosRepoImpl.kt
class TodosRepoImpl @Inject constructor(private val api: Api, private val dao: TodoDao): TodosRepo {
override suspend fun list(): List<String> = networkBoundResource(
query = { dao.getAll().takeIf { it.isNotEmpty() }?.map { it.title } },
fetch = { api.getTodos().map { it.name } },
saveFetchResult = { items -> dao.insertAll(items.map { TodoEntity(id = it, title = it) }) },
)
}
// ui/TodosScreen.kt
@Composable
fun TodosScreen(vm: TodoViewModel = hiltViewModel()) {
val state by vm.state.collectAsStateWithLifecycle()
when (state) {
is TodoViewModel.UiState.Loading -> CircularProgressIndicator()
is TodoViewModel.UiState.Error -> Text((state as TodoViewModel.UiState.Error).message)
is TodoViewModel.UiState.Success -> LazyColumn { items((state as TodoViewModel.UiState.Success).items) { Text(it) } }
is TodoViewModel.UiState.Idle -> Button({ vm.load() }) { Text("Load") }
}
}
Notes
TodoDto and TodoEntity with your schema; add Paging 3 for long lists.Paste into Android Studio project (see sandboxes/android-compose):