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| Paging3 适用于 数据库 + API 组合加载，完整示例如下：
1.创建 Entity（数据库表）
@Entity(tableName = "users")
public class User {
@PrimaryKey
public int id;
public String name;
}
2.创建 Dao（数据库查询）
@Dao
public interface UserDao {
@Query("SELECT * FROM users ORDER BY id ASC")
PagingSource<Integer, User> getUsers();
}
3.创建 RemoteMediator（远程 + 本地数据源）
@OptIn(ExperimentalPagingApi.class)
public class UserRemoteMediator extends RemoteMediator<Integer, User> {
private final UserDao userDao;
private final ApiService apiService;
public UserRemoteMediator(UserDao userDao, ApiService apiService) {
this.userDao = userDao;
this.apiService = apiService;
}
@NonNull
@Override
public MediatorResult load(@NonNull LoadType loadType, @NonNull PagingState<Integer, User> state) {
try {
int page = state.getAnchorPosition() != null ? state.getAnchorPosition() / 20 : 1;
List<User> users = apiService.getUsers(page);
userDao.insertAll(users);
return new MediatorResult.Success(users.isEmpty());
} catch (Exception e) {
return new MediatorResult.Error(e);
}
}
}
4.创建 Repository（数据提供层）
public class UserRepository {
private final UserDao userDao;
private final ApiService apiService;
public UserRepository(UserDao userDao, ApiService apiService) {
this.userDao = userDao;
this.apiService = apiService;
}
public Flow<PagingData<User>> getUsers() {
return new Pager(
new PagingConfig(20), // 每页大小
() -> userDao.getUsers()
).getFlow();
}
}
5.创建 ViewModel
@HiltViewModel
public class UserViewModel extends ViewModel {
private final UserRepository repository;
public LiveData<PagingData<User>> userPagingData;
@Inject
public UserViewModel(UserRepository repository) {
this.repository = repository;
userPagingData = PagingLiveData.cachedIn(repository.getUsers(), viewModelScope);
}
}
6.创建 Adapter（PagingDataAdapter）
public class UserAdapter extends PagingDataAdapter<User, UserAdapter.UserViewHolder> {
public UserAdapter() {
super(DIFF_CALLBACK);
}
@NonNull
@Override
public UserViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
return new UserViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.item_user, parent, false));
}
@Override
public void onBindViewHolder(@NonNull UserViewHolder holder, int position) {
User user = getItem(position);
if (user != null) {
holder.bind(user);
}
}
private static final DiffUtil.ItemCallback<User> DIFF_CALLBACK =
new DiffUtil.ItemCallback<User>() {
@Override
public boolean areItemsTheSame(@NonNull User oldItem, @NonNull User newItem) {
return oldItem.id == newItem.id;
}
@Override
public boolean areContentsTheSame(@NonNull User oldItem, @NonNull User newItem) {
return oldItem.equals(newItem);
}
};
static class UserViewHolder extends RecyclerView.ViewHolder {
public UserViewHolder(@NonNull View itemView) {
super(itemView);
}
void bind(User user) {
((TextView) itemView.findViewById(R.id.userName)).setText(user.name);
}
}
}
7.在 Activity / Fragment 中使用
public class MainActivity extends AppCompatActivity {
private UserViewModel userViewModel;
private UserAdapter userAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
userViewModel = new ViewModelProvider(this).get(UserViewModel.class);
RecyclerView recyclerView = findViewById(R.id.recyclerView);
userAdapter = new UserAdapter();
recyclerView.setAdapter(userAdapter);
userViewModel.userPagingData.observe(this, pagingData -> userAdapter.submitData(getLifecycle(), pagingData));
}
}
public class MainActivity extends AppCompatActivity {
private UserViewModel userViewModel;
private UserAdapter userAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
userViewModel = new ViewModelProvider(this).get(UserViewModel.class);
RecyclerView recyclerView = findViewById(R.id.recyclerView);
userAdapter = new UserAdapter();
recyclerView.setAdapter(userAdapter);
userViewModel.userPagingData.observe(this, pagingData -> userAdapter.submitData(getLifecycle(), pagingData));
}
}
|