本文介绍了使用LiveData从网络刷新数据的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我正在研究可查询github api以获得用户列表的应用，而我正在遵循推荐的android 架构组件指南.从网络中获取数据后，我将使用Room DB将其存储在本地，然后使用在LiveData对象上观察到的ViewModel将其显示在UI上(这很好).但是，我希望有一个按钮，当单击该按钮时，当且仅当存在网络连接时，该按钮才会触发刷新操作并执行网络请求以从API中获取新数据.问题是，当我单击该按钮时，将触发两个网络调用，一个来自refreshUserData()，另一个来自已存在的LiveData(在onCreate()期间触发).我应该如何最好地处理这种情况，以使我的刷新按钮仅执行一个网络请求，而不执行两个网络请求.这是我的存储库类:
I am working on an app that queries the github api to get a list of user and i'm following the recommended android architecture component guide. Once the data is fetched from the network, I store it locally using Room DB and then display it on the UI using ViewModel that observes on the LiveData object (this works fine). However, I want to be able to have a button which when clicked would trigger a refresh action and perform a network request to get new data from the API if and only if there is a network connection.The issue is when I click the button, two network calls are triggered, one from the refreshUserData() and the other one from the already existing LiveData that was triggered during onCreate(). How best should I handle this situation such that my refresh button performs only one network request and not two as is the case.Here's my Repository class:
public class UserRepository {
private final UserDao mUserDao;
private LiveData<List<GitItem>> mAllUsers;
private LiveData<GitItem> mUser;
private final GithubUserService githubUserService;
private final AppExecutors appExecutors;
private final Application application;
private static String LOG_TAG = UserRepository.class.getSimpleName();
private RateLimiter<String> repoListRateLimit = new RateLimiter<>(1, TimeUnit.MINUTES);
public UserRepository(Application application, GithubUserService githubUserService, AppExecutors appExecutors) {
this.application = application;
UserRoomDatabase db = UserRoomDatabase.getDatabase(application);
mUserDao = db.userDao();
this.githubUserService = githubUserService;
this.appExecutors = appExecutors;
}
public LiveData<GitItem> getUser(int userId) {
LiveData<GitItem> user = mUserDao.loadUser(userId);
Log.d(LOG_TAG, "retrieved user from database successful");
return user;
}
public LiveData<Resource<List<GitItem>>> getAllUsers() {
//ResultType, RequestType
/**
* List<GitItem> is the [ResultType]
* GithubUser is the [RequestType]
*/
return new NetworkBoundResource<List<GitItem>, GithubUser>(appExecutors) {
@Override
protected void saveCallResult(@NonNull GithubUser item) {
Log.d(LOG_TAG, "call to insert results to db");
mUserDao.insertUsers(item.getItems());
}
@Override
protected boolean shouldFetch(@Nullable List<GitItem> data) {
Log.d(LOG_TAG, "null?" + (data == null));
Log.d(LOG_TAG, "empty? " + (data.isEmpty()));
Log.d(LOG_TAG, "rate? " + (repoListRateLimit.shouldFetch("owner")));
Log.d(LOG_TAG, "should fetch? " + (data.isEmpty() || repoListRateLimit.shouldFetch("owner")));
return data.isEmpty() || data == null;
}
@NonNull
@Override
protected LiveData<List<GitItem>> loadFromDb() {
Log.d(LOG_TAG, " call to load from db");
return mUserDao.getAllUsers();
}
@NonNull
@Override
protected LiveData<ApiResponse<GithubUser>> createCall() {
Log.d(LOG_TAG, "creating a call to network");
return githubUserService.getGithubUsers("language:java location:port-harcourt");
}
@Override
protected GithubUser processResponse(ApiResponse<GithubUser> response) {
return super.processResponse(response);
}
}.asLiveData();
}
public LiveData<Resource<List<GitItem>>> refreshUserData() {
//ResultType, RequestType
/**
* List<GitItem> is the [ResultType]
* GithubUser is the [RequestType]
*/
return new NetworkBoundResource<List<GitItem>, GithubUser>(appExecutors) {
@Override
protected void saveCallResult(@NonNull GithubUser item) {
Log.d(LOG_TAG, "call to insert results to db");
mUserDao.insertUsers(item.getItems());
}
@Override
protected boolean shouldFetch(@Nullable List<GitItem> data) {
Log.d(LOG_TAG, "refreshUserData");
return true;
}
@NonNull
@Override
protected LiveData<List<GitItem>> loadFromDb() {
Log.d(LOG_TAG, "refreshUserData");
Log.d(LOG_TAG, " call to load from db");
return mUserDao.getAllUsers();
}
@NonNull
@Override
protected LiveData<ApiResponse<GithubUser>> createCall() {
Log.d(LOG_TAG, "refreshUserData");
Log.d(LOG_TAG, "creating a call to network");
return githubUserService.getGithubUsers("language:java location:port-harcourt");
}
@Override
protected GithubUser processResponse(ApiResponse<GithubUser> response) {
return super.processResponse(response);
}
}.asLiveData();
}
public Application getApplication() {
return application;
}
}
我的ViewModel类是:
My ViewModel Class is:
public class UserProfileViewModel extends AndroidViewModel {
private UserRepository mRepository;
public UserProfileViewModel(UserRepository mRepository) {
super(mRepository.getApplication());
this.mRepository = mRepository;
}
public LiveData<Resource<List<GitItem>>> getmAllUsers() {
return mRepository.getAllUsers();
}
public LiveData<Resource<List<GitItem>>> refreshUserData() {
return mRepository.refreshUserData();
}
public LiveData<GitItem> getUser(int userId) {
return mRepository.getUser(userId);
}
}
我的MainActivity类:
My MainActivity class:
public class MainActivity extends AppCompatActivity implements GithubAdapter.ListItemClickListener {
private RecyclerView mRecyclerView;
private UserProfileViewModel mUserViewModel;
public static final String USER_ID = "userId";
private ConnectivityManager cm;
private boolean isConnected;
private UserRepository mRepository;
private GithubUserService mGithubUserService;
private NetworkInfo activeNetwork;
private Picasso mPicasso;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
mGithubUserService = GithubApplication.get(MainActivity.this).getGithubUserService();
mPicasso = GithubApplication.get(MainActivity.this).getPicasso();
mRepository = new UserRepository(getApplication(), mGithubUserService, new AppExecutors());
// the factory and its dependencies instead should be injected with DI framework like Dagger
ViewModelFactory factory = new ViewModelFactory(mRepository);
mUserViewModel = ViewModelProviders.of(this, factory).get(UserProfileViewModel.class);
// initViews();
mRecyclerView = findViewById(R.id.users_recycler);
final GithubAdapter mAdapter = new GithubAdapter(this, this, mPicasso);
mRecyclerView.setAdapter(mAdapter);
mRecyclerView.setHasFixedSize(true);
mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
cm = (ConnectivityManager) this.getSystemService(Context.CONNECTIVITY_SERVICE);
getUsers(mAdapter);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//check if there is a network connection
// if there is a network connection the LoaderManager is called but
// displays a message if there's no network connection
activeNetwork = cm.getActiveNetworkInfo();
isConnected = activeNetwork != null && activeNetwork.isConnectedOrConnecting();
if (isConnected) {
mUserViewModel.refreshUserData().observe(MainActivity.this, new Observer<Resource<List<GitItem>>>() {
@Override
public void onChanged(@Nullable Resource<List<GitItem>> listResource) {
// Toast.makeText(MainActivity.this, "second" + listResource.status, Toast.LENGTH_LONG).show();
Snackbar.make(view, "refresh:" + listResource.status, Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
mAdapter.setUsers(listResource.data);
}
});
} else {
Snackbar.make(view, "no connection", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
}
});
}
private void getUsers(GithubAdapter mAdapter) {
mUserViewModel.getmAllUsers().observe(this, new Observer<Resource<List<GitItem>>>() {
@Override
public void onChanged(@Nullable Resource<List<GitItem>> listResource) {
Toast.makeText(MainActivity.this, "" + listResource.status, Toast.LENGTH_LONG).show();
mAdapter.setUsers(listResource.data);
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
@Override
public void onListItemClick(int userId) {
Intent detailIntent = new Intent(MainActivity.this,
DetailActivity.class);
detailIntent.putExtra(USER_ID, userId);
startActivity(detailIntent);
}
}
您可以在此处
推荐答案
最好的方法是使用onCreate方法在MainActivity中注册LiveData并像您一样侦听数据库更改.在FAB onClick中，只需发出网络请求，然后将其保存到不带LiveData的数据库中即可. onCreate方法中的LiveData将被触发.
The best way is to register your LiveData in the MainActivity in onCreate method and listen for db changes like you did. In the FAB onClick just make network request and save it to db without LiveData. LiveData in onCreate method will be triggered.
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