我无法找到合适的解决方案来让view / viewmodel了解网络状态，特别是使用RxJava。
我尝试关注Google's NetworkBoundResource和Iammert's networkBoundResouce（也试过GithubBrowserSample 但我真的不明白代码或它应该如何封装。
我正在寻找如何使用RxJava2实现NetworkBoundResource，以便数据通过数据库自动刷新。
我将展示我目前拥有的东西：
具有arch.lifecycle.ViewModel
的片段public class LoginViewModel extends ViewModel {
static final int SCREEN_JUST_BUTTONS = 0;
static final int SCREEN_LOGIN_INPUT = 1;
static final int SCREEN_PASS_INPUT = 2;
// using a PublishSubject because we are not interested in the last object that was emitted
// before subscribing. Like this we avoid displaying the snackbar multiple times
@NonNull
private final PublishSubject<Integer> snackbarText;
private int SCREEN = 0;
private LoginUiModel loginUiModel;
@NonNull
private BaseSchedulerProvider schedulerProvider;
@NonNull
private UserRepository userRepository;
@Inject
LoginViewModel(@NonNull final BaseSchedulerProvider schedulerProvider, @NonNull final UserRepository userRepository) {
this.schedulerProvider = schedulerProvider;
this.userRepository = userRepository;
snackbarText = PublishSubject.create();
disposables = new CompositeDisposable();
loginUiModel = new LoginUiModel();
}
int getScreen() {
return SCREEN;
}
void setScreen(final int screen) {
this.SCREEN = screen;
}
@NonNull
Observable<Integer> getSnackbarText() {
return snackbarText;
}
LoginUiModel getLoginUiModel() {
return loginUiModel;
}
public Single<User> login(final String login, final String password) {
return userRepository.login(login, password)
.subscribeOn(schedulerProvider.io())
.observeOn(schedulerProvider.ui())
.doOnError(this::handleErrorLogin);
}
private void handleErrorLogin(final Throwable t) {
if (t instanceof HttpException) {
showSnackbar(R.string.Login_invalid_input);
} else if (t instanceof IOException) {
showSnackbar(R.string.Common_no_connection);
} else {
showSnackbar(R.string.Common_error_loading);
}
}
private void showSnackbar(@StringRes int textId) {
snackbarText.onNext(textId);
}
void forgotPassword() {
if (isValidEmail(loginUiModel.getEmail())) {
showSnackbar(R.string.Login_password_sent);
} else {
showSnackbar(R.string.Login_invalid_login);
}
//TODO;
}
boolean isValidEmail(@Nullable final String text) {
return text != null && text.trim().length() > 3 && text.contains("@");
}
}
并在我的UserRepository中：
@Singleton
public class UserRepository {
@NonNull
private final UserDataSource userRemoteDataSource;
@NonNull
private final UserDataSource userLocalDataSource;
@NonNull
private final RxSharedPreferences preferences;
@Inject
UserRepository(@NonNull RxSharedPreferences rxSharedPreferences, @NonNull @Remote UserDataSource userRemoteDataSource, @NonNull @Local UserDataSource
userLocalDataSource) {
this.userRemoteDataSource = userRemoteDataSource;
this.userLocalDataSource = userLocalDataSource;
preferences = rxSharedPreferences;
}
@NonNull
public Single<User> login(final String email, final String password) {
return userRemoteDataSource
.login(email, password) // busca do webservice
.flatMap(userLocalDataSource::saveUser) // salva no banco local
.flatMap(user -> userLocalDataSource.login(user.getEmail(), user.getPassword())) // busca usuário no banco local como SSOT
.doOnSuccess(this::saveUserId); // salva o ID do usuário nas preferências.
}
public Single<User> saveUser(String email, String password, String name, String phone, String company) {
User user = new User(0, name, email, password, phone, company);
return saveUser(user);
}
private Single<User> saveUser(final User user) {
return userRemoteDataSource.saveUser(user)
.flatMap(userLocalDataSource::saveUser)
.doOnSuccess(this::saveUserId); // salva o ID do usuário nas preferências.
}
private void saveUserId(final User user) {
preferences.getLong(Consts.KEY_USER_ID__long).set(user.getUserId());
}
public Flowable<User> getUserUsingSystemPreferences() {
Preference<Long> userIdPref = preferences.getLong(Consts.KEY_USER_ID__long, -1L);
if (userIdPref.get() <= 0) {
//nao deveria acontecer, mas se acontecer, reseta:
userIdPref.delete();
return Flowable.error(new RuntimeException("Not logged in."));
} else if (!userIdPref.isSet()) {
return Flowable.error(new RuntimeException("Not logged in."));
} else {
return userLocalDataSource.getUser(String.valueOf(userIdPref.get()));
}
}
}
和我的UserLocalDataSource：
@Singleton
public class UserLocalDataSource implements UserDataSource {
private final UserDao userDao;
@Inject
UserLocalDataSource(UserDao userDao) {
this.userDao = get(userDao);
}
@NonNull
@Override
public Single<User> login(final String email, final String password) {
return userDao.login(email, password);
}
@Override
public Flowable<User> getUser(final String id) {
return userDao.getUserById(Long.valueOf(id));
}
@Override
public Single<User> saveUser(final User user) {
return Single.create(e -> {
long id = userDao.insert(user);
user.setUserId(id);
e.onSuccess(user);
});
}
@Override
public Completable deleteUser(final String id) {
return getUser(id).flatMapCompletable(user -> Completable.create(e -> {
int numberOfDeletedRows = userDao.delete(user);
if (numberOfDeletedRows > 0) {
e.onComplete();
} else {
e.onError(new Exception("Tried to delete a non existing user"));
}
}));
}
}
和用户远程数据源：
public class UserRemoteDataSource implements UserDataSource {
private final ISApiService apiService;
@Inject
UserRemoteDataSource(ISApiService apiService) {
this.apiService = get(apiService);
}
@NonNull
@Override
public Single<User> login(final String email, final String password) {
return apiService.login(email, password);
}
@Override
public Flowable<User> getUser(final String id) {
throw new RuntimeException("NO getUser endpoint");
}
@Override
public Single<User> saveUser(final User user) {
Map<String, String> params = new HashMap<>();
params.put(ISApiConsts.EMAIL, user.getEmail());
params.put(ISApiConsts.NAME, user.getName());
params.put(ISApiConsts.PASSWORD, user.getPassword());
params.put(ISApiConsts.PHONE, user.getPhone());
params.put(ISApiConsts.COMPANY, user.getCompany());
return apiService.signUp(params);
}
@Override
public Completable deleteUser(final String id) {
//can't delete user.
return Completable.complete();
}
}
UserDao界面（正在使用房间）
@Dao
public interface UserDao extends BaseDao<User> {
@Query("SELECT * FROM user WHERE user_id = :id")
Flowable<User> getUserById(long id);
@Query("SELECT * FROM user WHERE email = :login AND password = :password")
Single<User> login(String login, String password);
}
我想知道的是：我如何封装我的域，同时仍然可以访问网络等可能出现的问题，并使用MVVM模式中的RxJava向用户显示它？
答案 0 :(得分：0)
首先让我复制过去，从Github浏览器样本中获取网络方法。
private void fetchFromNetwork(final LiveData<ResultType> dbSource) {
LiveData<ApiResponse<RequestType>> apiResponse = createCall();
// we re-attach dbSource as a new source, it will dispatch its latest value quickly
result.addSource(dbSource, newData -> setValue(Resource.loading(newData)));
result.addSource(apiResponse, response -> {
result.removeSource(apiResponse);
result.removeSource(dbSource);
//noinspection ConstantConditions
if (response.isSuccessful()) {
appExecutors.diskIO().execute(() -> {
saveCallResult(processResponse(response));
appExecutors.mainThread().execute(() ->
// we specially request a new live data,
// otherwise we will get immediately last cached value,
// which may not be updated with latest results received from network.
result.addSource(loadFromDb(),
newData -> setValue(Resource.success(newData)))
);
});
} else {
onFetchFailed();
result.addSource(dbSource,
newData -> setValue(Resource.error(response.errorMessage, newData)));
}
});
}
我从这个片段中了解到，你真的不监视网络状态，但应用程序只是尝试点击服务器，当它成功响应它发布到状态为“成功”的UI时，如果它无法从服务器获取数据，则会触发onFetchFailed()方法，并将数据库数据设置为状态为“失败”的检索数据。
如果您决定使用失败的消息显示缓存数据，我认为您需要状态。
NetworkBoundResource类中还有许多其他抽象方法，因此您可以在没有获得新数据时选择正确的操作。
说到Rxjava，我正在使用iammert repo的fork来使用Rxjava我会在完成它之后在这里分享链接。