RecyclerView 即使在收到数据后也没有显示任何内容

Question

我正在尝试在 RecyclerView 上填充一些数据。通过其中一种方式获取数据：

如果互联网存在（使用Retrofit和RxJava2），从API请求数据，将数据保存到本地数据库（使用Room），发送数据到 View（在我的例子中是 Fragment）。
如果没有互联网则从本地数据库获取数据并将其发送到View。

我使用 MVP 作为应用程序架构，我使用 ViewModels 来处理 UI 的数据处理。我正在使用 ButterKnife 进行视图查找。

Presenter调用Repository，根据上面指定的条件获取数据，然后Presenter将数据发送到Views where ViewModel 拦截数据并执行必要的步骤将数据传递给 UI 元素（RecyclerView 适配器更新）。

我的问题是：

即使我在调试器中看到数据到达 RecyclerViewAdapter，屏幕也是空白的。没有显示数据。
本地数据库的结果抛出IllegalStateException，表示无法从主线程访问本地数据库，即使我subscribeOn(Schedulers.io())调用函数return 来自本地数据库的数据，其中 return 一个 Maybe<>。

我的代码如下：
存储库：

public class CountriesListApiRepository {
    private final IRestServiceDataFetcher restServiceDataFetcher; // Retrofit interface to get data from API

    @Inject
    public CountriesListApiRepository(IRestServiceDataFetcher restServiceDataFetcher) {
        this.restServiceDataFetcher = restServiceDataFetcher;
    }

    public Maybe<List<CountriesFullEntity>> getCountriesFromApi() {
        return restServiceDataFetcher
                .getListOfCountriesData()
                .observeOn(AndroidSchedulers.mainThread())
                .subscribeOn(Schedulers.io());
    }
}

public class CountriesListLocalDbRepository {
    private final CountriesLocalDb countriesLocalDb;

    @Inject
    CountriesListLocalDbRepository(CountriesLocalDb countriesLocalDb) {
        this.countriesLocalDb = countriesLocalDb;
    }

    Maybe<List<CountriesFullEntity>> getCountriesFromLocalDb() {
        return this.countriesLocalDb
                .getCountriesLocalDbDAO()
                .getCountriesList()
                .observeOn(Schedulers.io())
                .subscribeOn(Schedulers.io());
    }

    void updateLocalDb(List<CountriesFullEntity> updatedCountriesList) {
        countriesLocalDb.getCountriesLocalDbDAO().insertAllCountries(updatedCountriesList);

    }
}

public class CountriesListRepository {
    private final CountriesListApiRepository countriesListApiRepository;
    private final CountriesListLocalDbRepository countriesListLocalDbRepository;
    private static final String TAG_CountriesListRepository = "CountriesListRepository";

    @Inject
    public CountriesListRepository(CountriesListApiRepository countriesListApiRepository,
                                   CountriesListLocalDbRepository countriesListLocalDbRepository) {
        this.countriesListApiRepository = countriesListApiRepository;
        this.countriesListLocalDbRepository = countriesListLocalDbRepository;
    }

    public Maybe<List<CountriesFullEntity>> getCountries() {
        return this.countriesListApiRepository
                .getCountriesFromApi()
                .doOnSuccess(this.countriesListLocalDbRepository::updateLocalDb)
                .doOnError(throwable -> {
                    Log.d(TAG_CountriesListRepository,throwable.getMessage());
                    throwable.printStackTrace(); })
                .onErrorResumeNext(this.countriesListLocalDbRepository.getCountriesFromLocalDb());
    }
}

我的主持人：

public class BasePresenter<T extends BaseView> {
    @Inject
    T injectedView;

    private static final String TAG_BASE_PRESENTER = "BasePresenter";

    T getInjectedView() {
        return injectedView;
    }

    <V> void subscribeToObserver(Maybe<V> flowable, MaybeObserver<V> maybeObserver) {
        flowable.subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .doOnSubscribe(subscription -> Log.d(TAG_BASE_PRESENTER,"Subscribed"))
                .doOnSuccess(v -> Log.d(TAG_BASE_PRESENTER,"onNext() completed"))
                .subscribe(maybeObserver);
    }
}

public class CountriesListPresenter extends BasePresenter<CountriesListView>
        implements MaybeObserver<List<CountriesFullEntity>> {

    private static final String TAG_ListPresenter = "CountriesListPresenter";

    private final CountriesListRepository countriesListRepository;

    private Disposable disposable;

    @Inject
    public CountriesListPresenter(CountriesListRepository countriesListRepository) {
        this.countriesListRepository = countriesListRepository;
    }

    public void getCountries() {
        Maybe<List<CountriesFullEntity>> listOfCountriesData = this.countriesListRepository
                .getCountries();
        subscribeToObserver(listOfCountriesData, this);
    }

    public void updateCountriesList(@NonNull Boolean isInternetThere) {
        Maybe<List<CountriesFullEntity>> newCountriesFullData = this.countriesListRepository
                .updateCountriesList(isInternetThere);
        subscribeToObserver(newCountriesFullData,this);
    }

    @Override
    public void onSubscribe(Disposable d) {
        this.disposable = d;
    }

    @Override
    public void onSuccess(List<CountriesFullEntity> countriesFullEntities) {
        Log.d(TAG_ListPresenter,"Executing onNext()");
        getInjectedView().onLoadCountriesDataFull(countriesFullEntities);
    }

    @Override
    public void onError(Throwable e) {
        Log.d(TAG_ListPresenter,"Executing onError()",e);
        getInjectedView().onErrorEncountered(e.getMessage());
    }

    @Override
    public void onComplete() {
        if(!disposable.isDisposed()) disposable.dispose();
    }
}

我的观点：

public class MainActivity extends AppCompatActivity implements IFragmentToFragmentMediator, SwipeRefreshLayout.OnRefreshListener {

    public static final String TAG_MAIN_ACTIVITY = "MainActivity";

    public static final String TAG_LIST_FRAGMENT = "COUNTRY_LIST";
    public static final String TAG_DETAILS_FRAGMENT = "COUNTRY_DETAILS";

    @BindView(R.id.MainActSwipeRefreshLayout)
    SwipeRefreshLayout swipeRefreshLayout;

    private Unbinder unbinder;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        unbinder = ButterKnife.bind(this);
        swipeRefreshLayout.setOnRefreshListener(this);
        Configuration config = getResources().getConfiguration();
        Log.d(TAG_MAIN_ACTIVITY,"Main Activity View Created");
        if(config.smallestScreenWidthDp<600){
            CountriesListFrag countriesListFrag = new CountriesListFrag();
            conductFragmentTransaction(countriesListFrag,TAG_LIST_FRAGMENT, false, true);
            Log.d(TAG_MAIN_ACTIVITY,"Main Activity < 600 and portrait");
        }
    }

    @Override
    public void onBackPressed() {
        super.onBackPressed();
        FragmentManager fm = getSupportFragmentManager();
        if(getSupportFragmentManager().getBackStackEntryCount() > 1) {
            Fragment f = fm.findFragmentByTag(TAG_DETAILS_FRAGMENT);
            if (f instanceof  CountryDetailsFrag) fm.popBackStack();
            else this.finish();
        }
    }

    @Override
    public void onRefresh() {
        // TODO : Code the refreshing data callback here
        Fragment countryListFragment = returnNonNullRunningFragmentByTagName(TAG_LIST_FRAGMENT);
        Fragment countryDetailsFragment = returnNonNullRunningFragmentByTagName(TAG_DETAILS_FRAGMENT);
        makeViewsSignalUpdateOfData((CountriesListFrag)countryListFragment);
        makeViewsSignalUpdateOfData((CountryDetailsFrag)countryDetailsFragment);
    }

    @Override
    public void invokeDetailsFragmentOnListItemCLickedInListFragment(CountriesFullEntity countriesFullEntity) {
        CountryDetailsFrag countryDetailsFrag = CountryDetailsFrag.newInstance();
        Bundle data = new Bundle();
        data.putSerializable("data",countriesFullEntity);
        countryDetailsFrag.setArguments(data);
        conductFragmentTransaction(countryDetailsFrag, TAG_DETAILS_FRAGMENT, false, true);
    }

    @Override
    public void invokeDetailsFragmentOnListItemClickedInListFragmentViewModel() {

        CountryDetailsFrag countryDetailsFrag =
                (CountryDetailsFrag) getSupportFragmentManager().findFragmentByTag(TAG_DETAILS_FRAGMENT);

        if(countryDetailsFrag!=null && countryDetailsFrag.isVisible())
        conductFragmentTransaction(countryDetailsFrag, TAG_DETAILS_FRAGMENT, true, true);
    }

    private void makeViewsSignalUpdateOfData(BaseView view) {
        if(view != null) view.onPerformUpdateAction();
    }

    private Fragment returnNonNullRunningFragmentByTagName(String tagName) {
        Fragment fragmentForProcessing = getSupportFragmentManager().findFragmentByTag(tagName);
        if(fragmentForProcessing!=null && fragmentForProcessing.isVisible()) return fragmentForProcessing;
        return null;
    }

    private void conductFragmentTransaction(Fragment targetFragment, String tag, boolean addOrReplaceFlag, boolean backStackFlag) {
        FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
        if(addOrReplaceFlag)fragmentTransaction.replace(R.id.fragmentCanvas,targetFragment,tag);
        else fragmentTransaction.add(R.id.fragmentCanvas,targetFragment,tag);
        if(backStackFlag)fragmentTransaction.addToBackStack(null);
        fragmentTransaction.commit();
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        unbinder.unbind();
    }
}

public class CountriesListFrag extends Fragment implements CountriesListView {

    public static final String TAG_LIST_FRAGMENT = "ListFragment";

    @Inject
    Picasso picasso;
    @Inject
    CountriesListPresenter countriesListPresenter;

    private IFragmentToFragmentMediator listeningActivity;
    private Frag2FragCommViewModel frag2FragCommViewModel;

    @BindView(R.id.CountriesEntireHolderRV)
    RecyclerView countriesEntireHolderRV;
    private CountriesListRecyclerViewAdapter countriesListRecyclerViewAdapter;
    private Unbinder unbinder;

    public CountriesListFrag() {
    }

    @Override
    public void onAttach(Context context) {
        DaggerCountryComponents
                .builder()
                .appComponents(((CentralApplication)context.getApplicationContext())
                        .getAppComponents())
                .countryModule(new CountryModule(this))
                .build()
                .inject(this);
        super.onAttach(context);
        try{
            this.listeningActivity = (MainActivity) context;

            this.frag2FragCommViewModel = ViewModelProviders
                    .of((MainActivity) context)
                    .get(Frag2FragCommViewModel.class);
        } catch (ClassCastException e) {
            throw new ClassCastException(context.toString() + " must implement IFragmentToFragmentMediator");
        }
    }

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
    }

    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.fragment_countries_list, container, false);
        if(v!=null) this.unbinder = ButterKnife.bind(this,v);

        // Inflate the layout for this fragment
        initialize();
        this.countriesListPresenter.getCountries();
        setUpListItemClickListener();

        frag2FragCommViewModel
                .getLiveDataListOfCountriesData()
                .observe(this,countriesFullEntities ->
                        countriesListRecyclerViewAdapter.setCountriesFullEntityList(countriesFullEntities));
        Log.d(TAG_LIST_FRAGMENT,"List Fragment View Created");

        return v;
    }

    @Override
    public void onLoadCountriesDataFull(List<CountriesFullEntity> countriesFullData) {
//        this.countriesListRecyclerViewAdapter.setCountriesFullEntityList(countriesFullData);
        Log.d(TAG_LIST_FRAGMENT,"Data Received in List Fragment");
        Log.d(TAG_LIST_FRAGMENT,countriesFullData.get(0).getName());
        this.frag2FragCommViewModel.setListOfCountriesData(countriesFullData);
    }

    @Override
    public void onErrorEncountered(String errorMessage) {
        Toast.makeText(getContext(), errorMessage,Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onPerformUpdateAction() {
        callToPresenterToUpdateListOfCountriesOnInternetPresent(this.getContext());
    }

    private void initialize() {
        this.countriesEntireHolderRV = new RecyclerView(this.getContext());
        this.countriesListRecyclerViewAdapter = new CountriesListRecyclerViewAdapter(new ArrayList<>(),
                LayoutInflater.from(this.getContext()), this.picasso);

        this.countriesEntireHolderRV.setLayoutManager(new LinearLayoutManager(this.getContext()));
        this.countriesEntireHolderRV
                .addItemDecoration(new DividerItemDecoration(this.countriesEntireHolderRV.getContext()
                        ,DividerItemDecoration.VERTICAL));
        this.countriesEntireHolderRV.setAdapter(this.countriesListRecyclerViewAdapter);
        Log.d(TAG_LIST_FRAGMENT,"List Fragment init");
    }

    @Override
    public void onDestroyView() {
        super.onDestroyView();
        this.unbinder.unbind();
    }
}

public class CountriesListRecyclerViewAdapter extends RecyclerView.Adapter<CountriesListRecyclerViewAdapter.CountriesListViewHolder>{
    private List<CountriesFullEntity> countriesFullEntityList;
    private final LayoutInflater layoutInflater;
    private final Picasso picasso;
    private CountriesListRVClickListener countriesListRVClickListener;
    private int currentPosition;

    CountriesListRecyclerViewAdapter(List<CountriesFullEntity> countriesFullEntityList, LayoutInflater layoutInflater, Picasso picasso) {
        this.countriesFullEntityList = countriesFullEntityList;
        this.layoutInflater = layoutInflater;
        this.picasso = picasso;
        this.currentPosition = 0;
    }

    @NonNull
    @Override
    public CountriesListViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        return new CountriesListViewHolder(this.layoutInflater.inflate(R.layout.countries_list_layout,parent,false));
    }

    @Override
    public void onBindViewHolder(@NonNull CountriesListViewHolder holder, int position) {
        CountriesFullEntity countriesFullEntity = countriesFullEntityList.get(position);
        picasso.load(countriesFullEntity.getFlag()).into(holder.countryIcon);
        holder.nameOfCountry.setText(countriesFullEntity.getName());
    }

    @Override
    public int getItemCount() {
        return this.countriesFullEntityList.size();
    }

    void setItemClickListener(CountriesListRVClickListener itemClickListener) {
        this.countriesListRVClickListener = itemClickListener;
    }

    CountriesFullEntity getCountriesFullEntityAtPosition(int position) {
        return this.countriesFullEntityList.get(position);
    }

    void setCountriesFullEntityList(List<CountriesFullEntity> countriesFullEntityList) {
        this.countriesFullEntityList = countriesFullEntityList;
        notifyDataSetChanged();
    }

    int getCurrentPosition() {
        return currentPosition;
    }

    void setCurrentPosition(int currentPosition) {
        this.currentPosition = currentPosition;
    }

    class CountriesListViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {

        @BindView(R.id.NameOfCountry)
        TextView nameOfCountry;
        @BindView(R.id.CountryIcon)
        ImageView countryIcon;
        CountriesListViewHolder(View itemView) {
            super(itemView);
        }

        @Override
        public void onClick(View v) {
            countriesListRVClickListener.onListItemClicked(v,getAdapterPosition());
        }
    }
}

我的 DAO：

@Dao
public interface CountriesLocalDbDAO {
    @Query("SELECT * FROM Countries")
    Maybe<List<CountriesFullEntity>> getCountriesList();

    @Query("SELECT * FROM Countries WHERE name LIKE :countryName")
    Maybe<CountriesFullEntity> getCountryByName(String countryName);

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void insertAllCountries(List<CountriesFullEntity> countryList);

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void insertSingleCountry(CountriesFullEntity singleCountry);

    @Delete
    void deleteSingleCountry(CountriesFullEntity singleCountry);

    @Delete
    void endOfTheWorld(List<CountriesFullEntity> theWorld);
}

public interface IRestServiceDataFetcher {
    @GET("all")
    Maybe<List<CountriesFullEntity>> getListOfCountriesData();
    @GET("name/{name}")
    Maybe<CountriesFullEntity> getParticularCountry(@Path("name") String name);
}

我的布局：

ActivityMainLayout:

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout
android:id="@+id/fragmentCanvas"
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".ui.MainActivity">
    <android.support.v4.widget.SwipeRefreshLayout
        android:id="@+id/MainActSwipeRefreshLayout"
        android:layout_height="20dp"
        android:layout_width="match_parent">
    </android.support.v4.widget.SwipeRefreshLayout>
</FrameLayout>

片段列表布局：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".ui.countrieslist.CountriesListFrag">

    <!-- TODO: Update blank fragment layout -->


    <android.support.v7.widget.RecyclerView
        android:id="@+id/CountriesEntireHolderRV"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</LinearLayout>

RecyclerViewViewHolderLayout：

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ImageView
        android:id="@+id/CountryIcon"
        android:layout_width="80dp"
        android:layout_height="80dp"
        android:layout_marginEnd="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:contentDescription="@string/app_name"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:srcCompat="@drawable/ic_launcher_background" />

    <TextView
        android:id="@+id/NameOfCountry"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginEnd="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:text="@string/app_name"
        android:textSize="40sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toEndOf="@+id/CountryIcon"
        app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>

我的应用程序 build.gradle：

apply plugin: 'com.android.application'

android {
    compileSdkVersion 27
    defaultConfig {
        applicationId "shankhadeepghoshal.org.countrieslistapp"
        minSdkVersion 14
        //noinspection OldTargetApi
        targetSdkVersion 27
        multiDexEnabled true
        versionCode 1
        versionName "1.0"
        vectorDrawables.useSupportLibrary = true
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
        javaCompileOptions {
            annotationProcessorOptions {
                includeCompileClasspath = true
            }
        }
        externalNativeBuild {
            cmake {
                cppFlags "-std=c++14 -frtti -fexceptions"
            }
        }
        // multiDexEnabled true
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
    externalNativeBuild {
        cmake {
            path "CMakeLists.txt"
        }
    }
    compileOptions {
        targetCompatibility JavaVersion.VERSION_1_8
        sourceCompatibility JavaVersion.VERSION_1_8
    }
    buildToolsVersion '27.0.3'
}

dependencies {
    implementation fileTree(include: ['*.jar'], dir: 'libs')

    implementation 'com.google.dagger:dagger:2.16'
    annotationProcessor 'com.google.dagger:dagger-compiler:2.16'
    implementation 'com.google.dagger:dagger-android:2.16'
    implementation 'com.google.dagger:dagger-android-support:2.16'
    annotationProcessor 'com.google.dagger:dagger-android-processor:2.16'

    implementation 'io.reactivex.rxjava2:rxandroid:2.1.0'
    implementation 'io.reactivex.rxjava2:rxjava:2.2.0'

    implementation 'com.squareup.picasso:picasso:2.71828'

    implementation(
            [group: 'com.fasterxml.jackson.core', name: 'jackson-core', version: '2.9.6'],
            [group: 'com.fasterxml.jackson.core', name: 'jackson-databind', version: '2.9.6'],
            [group: 'com.fasterxml.jackson.core', name: 'jackson-annotations', version: '2.9.6']
    )

    implementation 'com.squareup.retrofit2:retrofit:2.4.0'
    implementation 'com.squareup.retrofit2:converter-jackson:2.4.0'
    implementation 'com.squareup.retrofit2:adapter-java8:2.4.0'
    implementation 'com.squareup.retrofit2:adapter-rxjava2:2.4.0'
    implementation 'com.squareup.okhttp3:logging-interceptor:3.5.0'

    compileOnly 'org.projectlombok:lombok:1.18.2'
    annotationProcessor 'org.projectlombok:lombok:1.18.2'

    def room_version = "1.1.1"
    implementation "android.arch.persistence.room:runtime:$room_version"
    annotationProcessor "android.arch.persistence.room:compiler:$room_version"
    implementation "android.arch.persistence.room:rxjava2:$room_version"
    implementation "android.arch.persistence.room:guava:$room_version"
    testImplementation "android.arch.persistence.room:testing:$room_version"

    def lifecycle_version = "1.1.1"
    implementation "android.arch.lifecycle:extensions:$lifecycle_version"
    implementation "android.arch.lifecycle:runtime:$lifecycle_version"
    implementation "android.arch.lifecycle:common-java8:$lifecycle_version"
    implementation "android.arch.lifecycle:reactivestreams:$lifecycle_version"
    testImplementation "android.arch.core:core-testing:$lifecycle_version"

    implementation 'com.jakewharton:butterknife:8.8.1'
    annotationProcessor 'com.jakewharton:butterknife-compiler:8.8.1'

    implementation 'com.android.support:design:27.1.1'
    implementation 'com.android.support:appcompat-v7:27.1.1'
    implementation 'com.android.support.constraint:constraint-layout:1.1.2'
    implementation 'com.android.support:recyclerview-v7:27.1.1'
    implementation 'com.android.support:support-compat:27.1.1'
    implementation 'com.android.support:exifinterface:27.1.1'
    implementation 'com.android.support:multidex:1.0.3'

    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.2'
    androidTestImplementation 'com.android.support.test:rules:1.0.2'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
}

更新：

我做了@Ben-P 在他的回答中建议的。但是现在我的 RecycleViewAdapter 给我错误。
我在这条线上得到一个 IllegalArgumentException - Target must be null ： picasso.load(countriesFullEntity.getFlag()).into(holder.countryIcon); in onBindViewHolder(holder,position)

Answer 1

在您的片段中，您有以下代码：

private void initialize() {
    this.countriesEntireHolderRV = new RecyclerView(this.getContext());
    ...
}

早些时候，在 onCreateView() 中，您调用 ButterKnife.bind()... 这意味着上面的代码正在将 countriesEntireHolderRV 重新分配给新的引用。这个新的 RecyclerView 永远不会添加到您的 Fragment 视图中（并且可能无论如何都不可见，因为 LinearLayout 已经有一个 child 占据了所有可见的 space），所以您的所有操作都与用户看不到的 RecyclerView。

只需从 initialize() 中删除该行即可。然后你将在你的布局文件中使用 RecyclerView，一切都会出现。

RecyclerView 即使在收到数据后也没有显示任何内容

RecyclerView not showing anything even after receiving data

android

android-recyclerview

rx-java2

android-room

android-mvp