我正在加载基于对RecyclerView的调用和存储在本地Retrofit数据库中的数据的SQLite。
在屏幕旋转时，RecyclerView保持重置状态。另外，当我喜欢电影时（将电影添加到我的本地房间数据库中），在某些情况下，微调器与RecyclerView中要填充的数据不一致。下面是我的代码：
public class MainActivity extends AppCompatActivity {
private RecyclerView mMovieResults;
private MyAdapter mMovieResultsAdapter;
private String query;
private String mBaseURL;
private int lastFirstVisiblePosition;
//TODO: How is someone able to load my API Key if I am storing it
private ArrayList<String> mMovieURLS;
private ArrayList<Movie> mMovies;
private List<Movie> mMovieResultsList;
private static final String SPINNER_SELECTION = "SPINNER_SELECTION";
private boolean mIsFavoriteSelected;
private AppDatabase mDb;
private Spinner mSpinner;
private SharedPreferences mPrefs;
private SharedPreferences.Editor mPrefsEditor;
private static Bundle mBundleRecyclerViewState;
private int saved_selection = -1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Log.v("ONCREATE", "ONCREATE");
if (savedInstanceState != null){
saved_selection = savedInstanceState.getInt(SPINNER_SELECTION);
}
if (isOnline()) {
setContentView(R.layout.activity_main);
Stetho.initializeWithDefaults(this);
mDb = AppDatabase.getInstance(getApplicationContext());
mMovieResults = findViewById(R.id.main_recyclerview_image_results);
GridLayoutManager glm = new GridLayoutManager(this, 3);
glm.setOrientation(LinearLayoutManager.VERTICAL);
mMovieResults.setLayoutManager(glm);
mMovieURLS = new ArrayList<>();
mMovies = new ArrayList<>();
mMovieResultsList = new ArrayList<>();
mMovieResultsAdapter = new MyAdapter(mMovieResultsList);
mMovieResults.setAdapter(mMovieResultsAdapter);
mDb = AppDatabase.getInstance(getApplicationContext());
mPrefs = getSharedPreferences("prefs", MODE_PRIVATE);
mPrefsEditor = mPrefs.edit();
switch (saved_selection){
case 0:
mBaseURL = "https://api.themoviedb.org/3/movie/popular/";
calltoRetrofit(mBaseURL);
break;
case 1:
mBaseURL = "https://api.themoviedb.org/3/movie/top_rated/";
calltoRetrofit(mBaseURL);
break;
case 2:
mIsFavoriteSelected = true;
mMovieURLS.clear();
retrieveMovies();
break;
default:
mBaseURL = "https://api.themoviedb.org/3/movie/popular/";
break;
}
} else {
setContentView(R.layout.activity_no_internet);
return;
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.action_bar_spinner, menu);
MenuItem item = menu.findItem(R.id.spinner);
mSpinner = (Spinner) item.getActionView();
if (isOnline()) {
ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(getApplicationContext(), R.array.spiner_list_item_array, R.layout.custom_spinner);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
mSpinner.setAdapter(adapter);
if (saved_selection >= 0){
mSpinner.setSelection(saved_selection);
}
mSpinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
@Override
public void onItemSelected(AdapterView<?> adapterView, View view, int i, long l) {
mPrefsEditor.putInt(SPINNER_SELECTION, i);
mPrefsEditor.commit();
switch (i) {
case 0:
mBaseURL = "https://api.themoviedb.org/3/movie/popular/";
calltoRetrofit(mBaseURL);
break;
case 1:
mBaseURL = "https://api.themoviedb.org/3/movie/top_rated/";
calltoRetrofit(mBaseURL);
break;
case 2:
mIsFavoriteSelected = true;
mMovieURLS.clear();
retrieveMovies();
break;
default:
mBaseURL = "https://api.themoviedb.org/3/movie/popular/";
break;
}
}
@Override
public void onNothingSelected(AdapterView<?> adapterView) {
}
});
return true;
} else {
return true;
}
}
@Override
protected void onSaveInstanceState(Bundle outState) {
outState.putInt(SPINNER_SELECTION, mSpinner.getSelectedItemPosition());
super.onSaveInstanceState(outState);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
super.onOptionsItemSelected(item);
int x = item.getItemId();
Log.v("OPTIONS_ID", String.valueOf(x));
return true;
}
private void retrieveMovies() {
//TODO: I am unsure if I am handling correctly. When I favorite and unfavorite a movie, and then go back to the MainActivity, it is not displaying the correct item from the Spinner.
//TODO: For example, favorites may be listed in the Spinner, however the screen may be displaying "TOP"
//TODO: How could I tell if I am making unnecessary queries to Room? I know it is a project requirement, but I was not sure how to handle if I am making unnecessary calls
//TODO: on screen rotation
MainViewModel viewModel = ViewModelProviders.of(this).get(MainViewModel.class);
final LiveData<List<Movie>> movies = viewModel.getMovies();
movies.observe(this, new Observer<List<Movie>>() {
@Override
public void onChanged(@Nullable final List<Movie> movies) {
for (Movie movie : movies) {
String photoURL = "http://image.tmdb.org/t/p/w185" + movie.getPoster_path();
Log.v("FAVORITE_URL", photoURL);
mMovieURLS.add(photoURL);
}
runOnUiThread(new Runnable() {
@Override
public void run() {
mMovieResultsList = movies;
mMovieResultsAdapter.notifyDataSetChanged();
}
});
}
});
}
@Override
protected void onResume() {
super.onResume();
((GridLayoutManager) mMovieResults.getLayoutManager()).scrollToPositionWithOffset(lastFirstVisiblePosition,0);
}
private void calltoRetrofit(String mBaseURL) {
mMovieURLS.clear();
HttpLoggingInterceptor interceptor = new HttpLoggingInterceptor();
interceptor.setLevel(HttpLoggingInterceptor.Level.BASIC);
OkHttpClient client = new OkHttpClient
.Builder()
.addInterceptor(interceptor)
.build();
Retrofit retrofit = new Retrofit.Builder()
.baseUrl(mBaseURL)
.client(client)
.addConverterFactory(GsonConverterFactory.create())
.build();
final ApiInterface apiInterface = retrofit.create(ApiInterface.class);
Log.v("API", API_KEY);
Call<Movies> call = apiInterface.getImages(API_KEY);
call.enqueue(new Callback<Movies>() {
@Override
public void onResponse(Call<Movies> call, Response<Movies> response) {
Log.v("RESPONSE", response.body().toString());
String totalPages = String.valueOf(response.body().getTotal_pages());
Log.v("TOTAL", totalPages);
mMovieResultsList = response.body().getResults();
for (Movie movie : mMovieResultsList) {
if (movie.getPoster_path() != null) {
String photoURL = "http://image.tmdb.org/t/p/w185" + movie.getPoster_path();
mMovieURLS.add(photoURL);
}
mMovieResultsAdapter.notifyDataSetChanged();
}
}
@Override
public void onFailure(Call<Movies> call, Throwable t) {
Log.v("FAILURE", t.toString());
}
});
}
@Override
public void onPointerCaptureChanged(boolean hasCapture) {
}
@Override
protected void onPause() {
super.onPause();
lastFirstVisiblePosition = ((GridLayoutManager)mMovieResults.getLayoutManager()).findFirstCompletelyVisibleItemPosition();
}
public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {
public class ViewHolder extends RecyclerView.ViewHolder {
protected ImageView mResultImage;
public ViewHolder(View itemView) {
super(itemView);
mResultImage = itemView.findViewById(R.id.movie_poster_image);
}
}
public MyAdapter(List<Movie> mDataset) {
mMovieResultsList = mDataset;
}
@NonNull
@Override
public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.movie_poster_image, parent, false);
return new ViewHolder(v);
}
@Override
public void onBindViewHolder(@NonNull ViewHolder holder, final int position) {
final String urlForPhoto = "http://image.tmdb.org/t/p/w185" + mMovieResultsList.get(position).getPoster_path();
Picasso.get()
.load(urlForPhoto)
.into(holder.mResultImage);
holder.itemView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent i = new Intent(getApplicationContext(), IndividualMovieActivity.class);
i.putExtra("Movie", mMovieResultsList.get(position));
startActivity(i);
}
});
}
@Override
public int getItemCount() {
return mMovieResultsList.size();
}
}
public interface ApiInterface {
@GET("?language=en-US")
Call<Movies> getImages(@Query("api_key") String api_key);
}
private boolean isOnline() {
ConnectivityManager cm =
(ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo netInfo = cm.getActiveNetworkInfo();
return netInfo != null && netInfo.isConnectedOrConnecting();
}
答案 0 :(得分：5)
RecyclerView仅保存其滚动位置，直到您调用setAdapter为止。通过在没有数据的情况下调用setAdapter，将放弃滚动位置（如果没有位置4，则无法滚动到位置4）。
您应该等到有数据呼叫setAdapter为止。
答案 1 :(得分：3)
旋转设备时，Android会检测到配置更改并默认情况下重新启动活动。这样，您的活动将再次调用适配器，并且recyclerview返回零位置。通过添加以下命令，您的意思是您可以自行处理此配置更改，因此android不会重新启动您的活动。
将此行添加到清单文件中的活动标签
android:configChanges="screenSize|orientation"
像这样：
<activity
android:name=".SearchActivity"
android:configChanges="screenSize|orientation"
android:label="@string/search"
android:theme="@style/AppTheme.NoActionBar">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>