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How can i make my request run in background while filling other EditTexts (Thread)?

I'm new to threading but I have an EditText view which whenever is getting out of focused it fills a RecyclerView with image logos using the user's input from EditText. But, whenever the user gets out of focuse and the method is called everything stops for a while(which mean im bad at threading). How can I improve this code so it can run smoothly?
My activity class:
public class addItem extends AppCompatActivity {
LoadingDialog loadingDialog;
RecyclerView imgList;
ArrayList<Bitmap> bitmapList = new ArrayList<>();
BitmapAdapter adapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
/*
/ Code Unnecessary to the problem…
*/
et_title.setOnFocusChangeListener((v, hasFocus) -> {
if(!hasFocus){
getImageLogo(et_title.getText().toString());
}
});
}
#SuppressLint("NotifyDataSetChanged")
private void getImageLogo(String serviceName){
googleRequest googleList = new googleRequest(serviceName);
googleList.start();
try {
googleList.join();
} catch (InterruptedException e) {
Log.e("Interrupted Error","Thread Was Interrupted unexpectedly",e);
}
if(googleList.getImgRealList() != null) {
bitmapList.clear();
bitmapList.addAll(googleList.getImgRealList());
}else {
bitmapList.clear();
}
adapter.notifyDataSetChanged();
}
My googleRequest class:
public class googleRequest extends Thread {
private ArrayList<Bitmap> imgRealList;
private final String keyword;
public googleRequest(String keyword){
this.keyword = keyword;
}
public ArrayList<Bitmap> getImgRealList() {
return imgRealList;
}
#Override
public void run() {
String newKeyword = keyword.toLowerCase(Locale.ROOT);
newKeyword = newKeyword.replace(' ','+');
String url = "https://www.google.gr/search?bih=427&biw=1835&hl=el&gbv=1&tbm=isch&og=&ags=&q="+ newKeyword;
try {
Document document = Jsoup.connect(url).get();
imgRealList = new ArrayList<>();
Elements imgList = document.select("img");
for (int i=1;i<imgList.size();i++) {
if(i==8)
break;
String imgSrc = imgList.get(i).absUrl("src");
InputStream input = new java.net.URL(imgSrc).openStream();
Bitmap bitmap = BitmapFactory.decodeStream(input);
imgRealList.add(bitmap);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}

Here is an example of how it can be implemented using a callback as I have mentioned in comments. For this, we need to define a callback inerface I named it as following, you can change the names for your convenience.
RequestConsumer it is simple java interface.
/// Must be executed in the UI (main) thread.
#MainThread
public interface RequestConsumer {
void onRequestResult(List<Bitmap> bitmaps);
}
googleRequest thread class.
public class googleRequest extends Thread {
private ArrayList<Bitmap> imgRealList;
private final String keyword;
/*
We will use the request consumer callback in order to deliver the results
to the UI from background. Since we need to touch the UI by this callback
we ensure that it will execute within the UI thread's queue using the
uiHandler.
*/
private final RequestConsumer requestConsumer;
private final Handler uiHandler = new Handler(Looper.getMainLooper());
public googleRequest(#NonNull String keyword, #NonNull RequestConsumer requestConsumer){
this.keyword = keyword;
this.requestConsumer = requestConsumer;
}
#Override
public void run() {
String newKeyword = keyword.toLowerCase(Locale.ROOT);
newKeyword = newKeyword.replace(' ','+');
String url = "https://www.google.gr/search?bih=427&biw=1835&hl=el&gbv=1&tbm=isch&og=&ags=&q="+ newKeyword;
try {
Document document = Jsoup.connect(url).get();
imgRealList = new ArrayList<>();
Elements imgList = document.select("img");
for (int i=1;i<imgList.size();i++) {
if(i==8)
break;
String imgSrc = imgList.get(i).absUrl("src");
InputStream input = new java.net.URL(imgSrc).openStream();
Bitmap bitmap = BitmapFactory.decodeStream(input);
imgRealList.add(bitmap);
}
// I think according to your code; the data you've requested is ready
// to deliver from now on. But attention! we post it to execute it in the UI thread
uiHandler.post(() -> requestConsumer.onRequestResult(imgRealList));
} catch (IOException e) {
e.printStackTrace();
}
}
}
addItem activity class
public class addItem extends AppCompatActivity {
LoadingDialog loadingDialog;
RecyclerView imgList;
ArrayList<Bitmap> bitmapList = new ArrayList<>();
BitmapAdapter adapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
/*
/ Code Unnecessary to the problem…
*/
et_title.setOnFocusChangeListener((v, hasFocus) -> {
if(!hasFocus){
getImageLogo(et_title.getText().toString());
}
});
}
#SuppressLint("NotifyDataSetChanged")
private void getImageLogo(String serviceName){
googleRequest googleList = new googleRequest(serviceName, images -> {
// Here we get the delivered results in this callback
if(images != null) {
bitmapList.clear();
bitmapList.addAll(images);
}else {
bitmapList.clear();
}
adapter.notifyDataSetChanged();
});
googleList.start();
}
}
Note I've written it in a text editor so the code needs some function test.

RecyclerView empty after data update

I am developing Android app which obtains information about restaurants from server and shows them in RecyclerView. When first package of information is obtained from server, everything works as expected, but, when I change search criteria and request new package of information from server, RecyclerView becomes blank. I used Toasts to debug what is coming from server and I am convinced that data is properly formatted. Also, variables that are used for accepting the data are also properly handled in code, according to my observations. Do you maybe know why my RecyclerView is empty when second package of data should be shown? Here is the code.
AfterLoginActivity.java
public class AfterLoginActivity extends AppCompatActivity {
/* interface main elements */
LinearLayout afterLoginLayout;
LinearLayout restaurantListLayout;
EditText restaurantEditText;
Button findRestaurantButton;
LoadingDialog loadingDialog;
AlphaAnimation loadingAnimation;
RecyclerView restaurantsRecyclerView;
int recycler_set = 0;
Button signOutButton;
GoogleSignInClient mGoogleSignInClient;
MyAdapter myAdapter = null;
/* server-client communication data */
public static String UploadUrl = "https://gdedakliknem.com/klopator.php";
public static String[] received;
String restaurants[] = new String[40];
String logos_as_strings[] = new String[40];
Bitmap logos[] = new Bitmap[40];
int num_of_elements = 0;
int data_received = 0;
/* user data */
String person_email;
String person_name;
String restaurant;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_after_login);
/* interface main elements */
afterLoginLayout = findViewById(R.id.afterLoginLayout);
restaurantListLayout = findViewById(R.id.restaurantListLayout);
restaurantEditText = findViewById(R.id.restaurantEditText);
findRestaurantButton = findViewById(R.id.findRestaurantButton);
restaurantsRecyclerView = findViewById(R.id.restaurantsRecyclerView);
signOutButton = findViewById(R.id.signOutButton);
loadingAnimation = new AlphaAnimation(1F, 0.8F);
loadingDialog = new LoadingDialog(AfterLoginActivity.this);
/* UPDATING INTERFACE ELEMENTS */
/* execution thread */
final Handler handler = new Handler();
final int delay = 2000; // 1000 milliseconds == 1 second
handler.postDelayed(new Runnable() {
public void run() {
/* check if recycler view is set */
if(recycler_set == 0){
/* if not, check if there is data to fil it with */
if(data_received == 1){
/* convert received strings to images */
for(int i = 0; i < num_of_elements; i++){
logos[i] = stringToBitmap(logos_as_strings[i]);
}
/* fill interface elements */
loadingDialog.dismissDialog();
myAdapter = new MyAdapter(AfterLoginActivity.this, restaurants, logos, num_of_elements);
restaurantsRecyclerView.setAdapter(myAdapter);
restaurantsRecyclerView.setLayoutManager(new LinearLayoutManager(AfterLoginActivity.this));
afterLoginLayout.setVisibility(View.GONE);
restaurantListLayout.setVisibility(View.VISIBLE);
recycler_set = 1;
}
}
handler.postDelayed(this, delay);
}
}, delay);
/* catch restaurant name from user's entry */
findRestaurantButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
restaurant = restaurantEditText.getText().toString();
if(!restaurant.isEmpty()){
view.startAnimation(loadingAnimation);
loadingDialog.startLoadingDialog();
sendRequest();
} else{
Toast.makeText(AfterLoginActivity.this, "Unesite naziv restorana!", Toast.LENGTH_LONG).show();
}
}
});
/* enable signing out */
GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
.requestEmail()
.build();
mGoogleSignInClient = GoogleSignIn.getClient(this, gso);
signOutButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
switch (view.getId()) {
case R.id.signOutButton:
signOut();
break;
}
}
});
/* obtaining email */
GoogleSignInAccount acct = GoogleSignIn.getLastSignedInAccount(this);
if (acct != null) {
person_email = acct.getEmail();
person_name = acct.getDisplayName();
}
}
#Override
public void onBackPressed() {
afterLoginLayout.setVisibility(View.VISIBLE);
restaurantsRecyclerView.setVisibility(View.GONE);
data_received = 0;
recycler_set = 0;
}
private void signOut() {
mGoogleSignInClient.signOut()
.addOnCompleteListener(this, new OnCompleteListener<Void>() {
#Override
public void onComplete(#NonNull Task<Void> task) {
Toast.makeText(AfterLoginActivity.this, "Signed out", Toast.LENGTH_LONG).show();
finish();
}
});
}
public void sendRequest(){
StringRequest stringRequest = new StringRequest(Request.Method.POST, UploadUrl, new Response.Listener<String>() {
#Override
public void onResponse(String response) {
try {
JSONObject jsonObject = new JSONObject(response);
String Response = jsonObject.getString("response");
if (Response.equals("Restaurant not found")){
loadingDialog.dismissDialog();
Toast.makeText(getApplicationContext(), "Uneti restoran ne postoji u sistemu! Proverite da li ste dobro napisali naziv", Toast.LENGTH_LONG).show();
} else{
received = Response.split(";");
if (received.length > 0){
data_received = 1;
num_of_elements = received.length / 2;
//Toast.makeText(getApplicationContext(), "num of elements: " + num_of_elements, Toast.LENGTH_LONG).show();
for(int i = 0; i < num_of_elements; i++){
logos_as_strings[i] = received[i*2];
restaurants[i] = received[i*2+1];
//Toast.makeText(getApplicationContext(), "restaurants: " + restaurants, Toast.LENGTH_LONG).show();
}
} else{
loadingDialog.dismissDialog();
Toast.makeText(getApplicationContext(), "Greška u prijemu", Toast.LENGTH_LONG).show();
}
}
} catch (JSONException e) {
e.printStackTrace();
}
}
}, new Response.ErrorListener() {
#Override
public void onErrorResponse(final VolleyError error) {
//volleyError = error;
}
})
{
#Override
protected Map<String, String> getParams() throws AuthFailureError {
//Toast.makeText(getApplicationContext(), "get params", Toast.LENGTH_LONG).show();
Map<String, String> params = new HashMap<>();
params.put("control", "find_restaurant");
params.put("restaurant", restaurant);
return params;
}
};
RequestQueue requestQueue = Volley.newRequestQueue(AfterLoginActivity.this);
requestQueue.add(stringRequest);
}
public static Bitmap stringToBitmap(String encodedString) {
try {
byte[] encodeByte = Base64.decode(encodedString, Base64.DEFAULT);
return BitmapFactory.decodeByteArray(encodeByte, 0, encodeByte.length);
} catch (Exception e) {
e.getMessage();
return null;
}
}
MyAdapter.java
public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> {
String restaurants[];
Bitmap logos[];
Context context;
int num_of_elements;
public MyAdapter(Context ct, String rests[], Bitmap lgs[], int num){
context = ct;
restaurants = rests;
logos = lgs;
num_of_elements = num;
Toast.makeText(context, Integer.toString(restaurants.length), Toast.LENGTH_LONG).show();
for(int i = 0; i < restaurants.length; i++){
Toast.makeText(context, restaurants[i], Toast.LENGTH_SHORT).show();
}
}
#NonNull
#Override
public MyViewHolder onCreateViewHolder(#NonNull ViewGroup parent, int viewType) {
LayoutInflater layoutInflater = LayoutInflater.from(context);
View view = layoutInflater.inflate(R.layout.restaurant_item_layout, parent, false);
return new MyViewHolder(view);
}
#Override
public void onBindViewHolder(#NonNull MyAdapter.MyViewHolder holder, int position) {
holder.restaurantNameTextView.setText(restaurants[position]);
holder.restaurantLogoImageView.setImageBitmap(logos[position]);
holder.restaurantItemLayout.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Intent intent = new Intent(context, AfterPickingRestaurantActivity.class);
ByteArrayOutputStream bs = new ByteArrayOutputStream();
logos[position].compress(Bitmap.CompressFormat.PNG, 50, bs);
intent.putExtra("byteArray", bs.toByteArray());
intent.putExtra("picked_restaurant_name", restaurants[position]);
context.startActivity(intent);
}
});
}
#Override
public int getItemCount() {
/*
int i = 0;
if (restaurants != null){
while(restaurants[i] != null){
i++;
}
} else{
i = restaurants.length;
}
return i;
*/
return num_of_elements;
}
public class MyViewHolder extends RecyclerView.ViewHolder {
TextView restaurantNameTextView;
ImageView restaurantLogoImageView;
LinearLayout restaurantItemLayout;
public MyViewHolder(#NonNull View itemView) {
super(itemView);
restaurantNameTextView = itemView.findViewById(R.id.restaurantNameTextView);
restaurantLogoImageView = itemView.findViewById(R.id.restaurantLogoImageView);
restaurantItemLayout = itemView.findViewById(R.id.restaurantItemLayout);
}
}

Add this lines after getting new data
myAdapter.notifyDataSetChanged()

Your Adapter Already set with RecyclerView in OnCreate Method.
so when'er you click on findRestaurantButton you just get Resturent data from server but collected data not pass in adapter so thats why to getting blank adapter..
Just put this line in your onResponse after set data in array..
myAdapter.notifyDataSetChanged()

I found out where is the mistake. If you take a look at the section where overriding of back button click is happening, I by mistake set to GONE recyclerView itself:
restaurantsRecyclerView.setVisibility(View.GONE);
instead of LinearLayout in which recyclerView is contained. Desired action was:
restaurantListLayout.setVisibility(View.GONE);
P.S. Everything works without calling notifyDataSetChanged(), I just create a new instance of myAdapater each time when I receive new data. I hope Garbage Collector is doing its job :)
Thanks everyone on help!

How to properly pass context to AsyncTask and then to another class?

I'm working on app that will use biometric as an option to login. Before I use the actual biometric prompt I need to check one thing from server - I use AsyncTask to do it. So, to sum up - I invoke AsyncTask from Parent Activity (login.java), and then AsyncTask uses biometricUtils.java class, that makes biometric prompt. The point is, I keep passing null instead of context to biometricUtils.java:
Attempt to invoke virtual method 'java.util.concurrent.Executor android.content.Context.getMainExecutor()' on a null object reference at biometricUtils.<init>(biometricUtils.java:34)
I have no idea to pass the context correctly.
Here's my code:
login.java
public class login extends AppCompatActivity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.login);
Bundle bundle = getIntent().getExtras();
final boolean flag = false;
final String androidID = bundle.getString("androidID");
final Activity thisActivity = this;
final Context context = getApplicationContext();
// login using biometrics
Button btnBiometricLogin = findViewById(R.id.btnBiometricLogin);
btnBiometricLogin.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
checkAndroidID async = new checkAndroidID(context);
async.getParentActivity(thisActivity);
async.setFlag(flag);
async.execute(androidID);
}
});
}
}
checkAndroidID.java
public class checkAndroidID extends AsyncTask <String, Void, String> {
openHTTP openHTTP = new openHTTP();
requestHTTP requests = new requestHTTP();
Activity parentActivity;
private WeakReference<Context> contextRef;
Boolean flag;
public checkAndroidID(Context context){
contextRef = new WeakReference<>(context);
}
public void getParentActivity(Activity parentActivity){
this.parentActivity = parentActivity;
}
public void setFlag (Boolean flag){
this.flag = flag;
}
#Override
protected String doInBackground(String... strings) {
try {
HttpURLConnection httpConn = openHTTP.prepareConnection("url");
String json = "{ \"androidID\": \"" + strings[0] + "\" }";
requests.sendData(json, httpConn);
return requests.receiveData(httpConn);
} catch (Exception e){
e.printStackTrace();
}
return null;
}
#Override
protected void onPostExecute(String s) {
String[] result = s.split(";");
Context ctx = contextRef.get();
if (result[0].equals("TRUE")) flag = true;
if (!flag) Toast.makeText(parentActivity, "Biometric authentication is now unavailable." +
" Please login using username and password", Toast.LENGTH_SHORT).show();
else {
biometricUtils biometrics = new biometricUtils(ctx);
biometrics.getParentActivity(parentActivity);
biometrics.getUsername(result[1]);
biometrics.inovkeBiometricPrompt();
}
super.onPostExecute(s);
}
}
and biometricUtlis.java
public class biometricUtils {
Activity parentActivity;
String username;
Context context;
public void getParentActivity(Activity parentActivity){
this.parentActivity = parentActivity;
}
public void getUsername(String s){
this.username = s;
}
public biometricUtils(Context context){
this.context = context;
}
// creating a variable for our Executor
Executor executor = ContextCompat.getMainExecutor(context); // LINE 34
// this will give us result of AUTHENTICATION
final BiometricPrompt biometricPrompt = new BiometricPrompt((FragmentActivity) parentActivity, executor, new BiometricPrompt.AuthenticationCallback() {
#Override
public void onAuthenticationError(int errorCode, #NonNull CharSequence errString) {
super.onAuthenticationError(errorCode, errString);
}
// THIS METHOD IS CALLED WHEN AUTHENTICATION IS SUCCESS
#Override
public void onAuthenticationSucceeded(#NonNull BiometricPrompt.AuthenticationResult result) {
super.onAuthenticationSucceeded(result);
Intent intent = new Intent(parentActivity.getApplicationContext(), tmp.class);
intent.putExtra("username", username);
parentActivity.startActivity(intent);
}
#Override
public void onAuthenticationFailed() {
super.onAuthenticationFailed();
}
});
// creating a variable for our promptInfo
// BIOMETRIC DIALOG
final BiometricPrompt.PromptInfo promptInfo = new BiometricPrompt.PromptInfo.Builder().setTitle("Biometrical login")
.setDescription("Place your fingerprint on scanner to proceed").setNegativeButtonText("Cancel").build();
public void inovkeBiometricPrompt() {
biometricPrompt.authenticate(promptInfo);
}
}

LiveData isn't being observed properly (gets null) when using Android Pagination Library

I am trying to update the UI depending on whether the data is being loaded or has loaded but it is not working properly. I am using enum class for different states.
Initially the error was
Attempt to invoke virtual method 'void androidx.lifecycle.LiveData.observe(androidx.lifecycle.LifecycleOwner, androidx.lifecycle.Observer)' on a null object reference
Then I passed an empty new MutableLiveData()<>. Now, it doesn't crashes the application, however, the getDataStatus() observer isn't working correctly. Kindly look at my implementations and see if they are right.
DataSource
public class ArticlesDataSource extends PageKeyedDataSource<Integer, NewsItem> {
private static final int FIRST_PAGE = 1;
private static final String TAG = "ArticlesDataSource";
public static final String SORT_ORDER = "publishedAt";
public static final String LANGUAGE = "en";
public static final String API_KEY = Utils.API_KEY;
public static final int PAGE_SIZE = 10;
private String mKeyword;
private MutableLiveData<DataStatus> dataStatusMutableLiveData = new MutableLiveData<>();
public ArticlesDataSource(String keyword) {
mKeyword = keyword;
dataStatusMutableLiveData = new MutableLiveData<>();
}
public MutableLiveData<DataStatus> getDataStatusMutableLiveData() {
return dataStatusMutableLiveData;
}
#Override
public void loadInitial(#NonNull LoadInitialParams<Integer> params, #NonNull LoadInitialCallback<Integer, NewsItem> callback) {
dataStatusMutableLiveData.postValue(DataStatus.LOADING);
NewsAPI newsAPI = ServiceGenerator.createService(NewsAPI.class);
Call<RootJsonData> call = newsAPI.searchArticlesByKeyWord(mKeyword, SORT_ORDER, LANGUAGE, API_KEY, FIRST_PAGE, PAGE_SIZE);
call.enqueue(new Callback<RootJsonData>() {
#Override
public void onResponse(Call<RootJsonData> call, Response<RootJsonData> response) {
if (response.body() != null) {
callback.onResult(response.body().getNewsItems(), null, FIRST_PAGE + 1);
dataStatusMutableLiveData.postValue(DataStatus.LOADED);
}
}
#Override
public void onFailure(Call<RootJsonData> call, Throwable t) {
Log.d(TAG, "onFailure: " + t.getMessage());
dataStatusMutableLiveData.postValue(DataStatus.ERROR);
}
});
}
#Override
public void loadBefore(#NonNull LoadParams<Integer> params, #NonNull LoadCallback<Integer, NewsItem> callback) {
NewsAPI newsAPI = ServiceGenerator.createService(NewsAPI.class);
Call<RootJsonData> call = newsAPI.searchArticlesByKeyWord(mKeyword, SORT_ORDER, LANGUAGE, API_KEY, FIRST_PAGE, PAGE_SIZE);
call.enqueue(new Callback<RootJsonData>() {
#Override
public void onResponse(Call<RootJsonData> call, Response<RootJsonData> response) {
// if the current page is greater than one
// we are decrementing the page number
// else there is no previous page
Integer adjacentKey = (params.key > 1) ? params.key - 1 : null;
if (response.body() != null) {
// passing the loaded data
// and the previous page key
callback.onResult(response.body().getNewsItems(), adjacentKey);
}
}
#Override
public void onFailure(Call<RootJsonData> call, Throwable t) {
Log.d(TAG, "onFailure: " + t.getMessage());
}
});
}
#Override
public void loadAfter(#NonNull LoadParams<Integer> params, #NonNull LoadCallback<Integer, NewsItem> callback) {
NewsAPI newsAPI = ServiceGenerator.createService(NewsAPI.class);
Call<RootJsonData> call = newsAPI.searchArticlesByKeyWord(mKeyword, SORT_ORDER, LANGUAGE, API_KEY, params.key, PAGE_SIZE);
call.enqueue(new Callback<RootJsonData>() {
#Override
public void onResponse(Call<RootJsonData> call, Response<RootJsonData> response) {
dataStatusMutableLiveData.postValue(DataStatus.LOADED);
if (response.code() == 429) {
// no more results
List<NewsItem> emptyList = new ArrayList<>();
callback.onResult(emptyList, null);
}
if (response.body() != null) {
// if the response has next page
// incrementing the next page number
Integer key = params.key + 1;
// passing the loaded data and next page value
if (!response.body().getNewsItems().isEmpty()) {
callback.onResult(response.body().getNewsItems(), key);
}
}
}
#Override
public void onFailure(Call<RootJsonData> call, Throwable t) {
Log.d(TAG, "onFailure: " + t.getMessage());
dataStatusMutableLiveData.postValue(DataStatus.ERROR);
}
});
}
}
DataSourceFactory
public class ArticlesDataSourceFactory extends DataSource.Factory {
private final MutableLiveData<ArticlesDataSource> itemLiveDataSource;
private String mQuery;
private final LiveData<DataStatus> dataStatusLiveData = Transformations.switchMap(itemLiveDataSource, (itemDataSource) -> {
return itemDataSource.getDataStatusMutableLiveData();
});
public ArticlesDataSourceFactory() {
mQuery = "news";
itemLiveDataSource = new MutableLiveData<>();
}
#Override
public DataSource<Integer, NewsItem> create() {
ArticlesDataSource itemDataSource = new ArticlesDataSource(mQuery);
itemLiveDataSource.postValue(itemDataSource);
// dataStatusMutableLiveData = itemDataSource.getDataStatusMutableLiveData();
return itemDataSource;
}
public MutableLiveData<ArticlesDataSource> getArticlesLiveDataSource() {
return itemLiveDataSource;
}
public void setQuery(String query) {
mQuery = query;
}
public MutableLiveData<DataStatus> getDataStatusMutableLiveData() {
return dataStatusMutableLiveData;
}
public void setDataStatusMutableLiveData(DataStatus dataStatus){
dataStatusMutableLiveData.postValue(dataStatus);
}
public LiveData<DataStatus> getDataStatusLiveData() {
return dataStatusLiveData;
}
}
ViewModel
public class ArticlesViewModel extends ViewModel {
public LiveData<PagedList<NewsItem>> itemPagedList;
private MutableLiveData<ArticlesDataSource> liveDataSource;
private ArticlesDataSourceFactory articlesDataSourceFactory;
private LiveData dataStatus = new MutableLiveData<>();
public ArticlesViewModel() {
articlesDataSourceFactory = new ArticlesDataSourceFactory();
liveDataSource = articlesDataSourceFactory.getArticlesLiveDataSource();
dataStatus = articlesDataSourceFactory.getDataStatusMutableLiveData();
PagedList.Config pagedListConfig =
(new PagedList.Config.Builder())
.setEnablePlaceholders(false)
.setPageSize(10).build();
itemPagedList = (new LivePagedListBuilder(articlesDataSourceFactory, pagedListConfig)).build();
}
public void setKeyword(String query) {
if (query.equals("") || query.length() == 0)
articlesDataSourceFactory.setDataStatusMutableLiveData(DataStatus.EMPTY);
else {
articlesDataSourceFactory.setQuery(query);
refreshData();
}
}
void refreshData() {
if (itemPagedList.getValue() != null) {
itemPagedList.getValue().getDataSource().invalidate();
}
}
public LiveData<DataStatus> getDataStatus() {
return dataStatus;
}
}
Fragment
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View rootView = inflater.inflate(R.layout.fragment_articles, container, false);
mContext = getActivity();
progressBar = rootView.findViewById(R.id.progress_circular);
emptyStateTextView = rootView.findViewById(R.id.empty_view);
swipeRefreshLayout = rootView.findViewById(R.id.swipe_refresh);
textViewTitle = rootView.findViewById(R.id.text_view_top_headlines);
recyclerView = rootView.findViewById(R.id.recycler_view);
if (savedInstanceState != null) {
keyword = savedInstanceState.getString("keyword");
}
initEmptyRecyclerView();
articlesViewModel = ViewModelProviders.of(this).get(ArticlesViewModel.class);
articlesViewModel.itemPagedList.observe(getViewLifecycleOwner(), new Observer<PagedList<NewsItem>>() {
#Override
public void onChanged(PagedList<NewsItem> newsItems) {
adapter.submitList(newsItems);
// TODO: Handle UI changes
// handleUIChanges(newsItems);
}
});
articlesViewModel.getDataStatus().observe(getViewLifecycleOwner(), new Observer<DataStatus>() {
#Override
public void onChanged(DataStatus dataStatus) {
switch (dataStatus) {
case LOADED:
progressBar.setVisibility(View.GONE);
emptyStateTextView.setVisibility(View.INVISIBLE);
swipeRefreshLayout.setRefreshing(false);
textViewTitle.setVisibility(View.VISIBLE);
break;
case LOADING:
progressBar.setVisibility(View.VISIBLE);
swipeRefreshLayout.setRefreshing(true);
textViewTitle.setVisibility(View.INVISIBLE);
emptyStateTextView.setVisibility(View.INVISIBLE);
break;
case EMPTY:
progressBar.setVisibility(View.GONE);
swipeRefreshLayout.setRefreshing(false);
textViewTitle.setVisibility(View.INVISIBLE);
emptyStateTextView.setVisibility(View.VISIBLE);
emptyStateTextView.setText(R.string.no_news_found);
break;
case ERROR:
progressBar.setVisibility(View.GONE);
swipeRefreshLayout.setRefreshing(false);
textViewTitle.setVisibility(View.INVISIBLE);
emptyStateTextView.setVisibility(View.VISIBLE);
emptyStateTextView.setText(R.string.no_internet_connection);
break;
}
}
});
swipeRefreshLayout.setOnRefreshListener(() -> {
articlesViewModel.setKeyword(keyword);
});
setHasOptionsMenu(true);
return rootView;
}
DataStatus
public enum DataStatus {
ERROR,
LOADING,
LOADED,
EMPTY
}

When you call invalidate(), a new datasource will be created by the factory. However, you are directly exposing the data status liveData of the "current" created datasource, without taking into consideration that more will be created in the future.
The solution is to store the current data source in the factory in a MutableLiveData, and expose the "most recent current data status" using switchMap.
public class ArticlesDataSourceFactory extends DataSource.Factory {
private final MutableLiveData<ArticlesDataSource> itemLiveDataSource = new MutableLiveData<>();
private String mQuery = "news";
private final LiveData<DataStatus> dataStatusLiveData = Transformations.switchMap(itemLiveDataSource, (itemDataSource) -> {
return itemDataSource.getDataStatusMutableLiveData();
});
public ArticlesDataSourceFactory() {
}
#Override
public DataSource<Integer, NewsItem> create() {
ArticlesDataSource itemDataSource = new ArticlesDataSource(mQuery);
itemLiveDataSource.postValue(itemDataSource);
...
public LiveData<DataStatus> getDataStatusLiveData() {
return dataStatusLiveData;
}

AsyncTaskLoader keeps reloading data when I come back to the MainActivity

I am quite new to the Android Development and I really need your help. My problem is in the MainActivity below. The app essentially displays a list of movies in the main activity and the movie details in another activity. And the problem is that whenever a user comes back from the MovieActivity to the MainActivity, the loader starts loading data again, although the movies are already there. And then it can not stop loading the data. It is really annoying. I want to get rid of this. So when a user comes back to the MainActivity, the loader will know that there is already loaded data and will not load anything again.If it helps, here is my full GitHub repo https://github.com/mateuszwojnarowicz/PopularMovies
I am stuck for about 3 weeks and have tried hundreds of possible solutions. Nothing seems to work. I feel really desperate.
Thank you so much for help,
Matthew
public class MainActivity extends AppCompatActivity implements LoaderManager.LoaderCallbacks<String> {
private MovieAdapter mAdapter;
private ArrayList<Movie> mMoviesCollection;
private SharedPreferences sharedPreferences;
private Resources resources;
private LoaderManager loaderManager;
private Loader<String> loader;
private RecyclerView.LayoutManager layoutManager;
private String sortBy;
#BindView(R.id.pb)
ProgressBar progressBar;
#BindView(R.id.er)
TextView errorTextView;
#BindView(R.id.rv)
RecyclerView recyclerView;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ButterKnife.bind(this);
mMoviesCollection = new ArrayList<Movie>();
sharedPreferences = getSharedPreferences(Constants.SHARED_PREFS, Activity.MODE_PRIVATE);
resources = getResources();
sortBy = sharedPreferences.getString(Constants.KEY_SORT, null);
setSharedPref();
layoutManager = new GridLayoutManager(this, calculateNoOfColumns(this));
loaderManager = getLoaderManager();
loader = loaderManager.getLoader(Constants.LOADER_MOVIES_ID);
initialize();
makeOperationLoadMovies(sortBy);
}
public static int calculateNoOfColumns(Context context) {
DisplayMetrics displayMetrics = context.getResources().getDisplayMetrics();
float dpWidth = displayMetrics.widthPixels / displayMetrics.density;
int noOfColumns = (int) (dpWidth / 150);
return noOfColumns;
}
//Set first-launch pref and set title according to pref
private void setSharedPref(){
if(!sharedPreferences.contains(Constants.KEY_SORT)) {
saveData(Constants.VALUE_POP);
setTitle(resources.getString(R.string.title_pop));
} else {
if (Objects.equals(sharedPreferences.getString(Constants.KEY_SORT, null), Constants.VALUE_POP)) {
setTitle(resources.getString(R.string.title_pop));
}
if (Objects.equals(sharedPreferences.getString(Constants.KEY_SORT, null), Constants.VALUE_TOP)) {
setTitle(resources.getString(R.string.title_top));
}
}
}
//Set up the RecyclerView
private void initialize(){
recyclerView.setLayoutManager(layoutManager);
recyclerView.setHasFixedSize(true);
mMoviesCollection = new ArrayList<>();
mAdapter = new MovieAdapter(mMoviesCollection, this, this);
recyclerView.setAdapter(mAdapter);
}
private void makeOperationLoadMovies(String SORT_BY){
Bundle bundle = new Bundle();
bundle.putString(Constants.LOADER_MOVIES_EXTRA, SORT_BY);
if(recyclerView.isDirty()){
}
else if(loader==null){
loaderManager.initLoader(Constants.LOADER_MOVIES_ID, bundle, this);
}else{
loaderManager.restartLoader(Constants.LOADER_MOVIES_ID, bundle, this);
}
}
//Update shared pref
private void saveData(String SORT_VALUE){
SharedPreferences.Editor editor = sharedPreferences.edit();
editor.putString(Constants.KEY_SORT, SORT_VALUE);
editor.apply();
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.main, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
switch (id){
case R.id.menu_fav:
startActivity(new Intent(MainActivity.this, FavoritesActivity.class));
break;
case R.id.menu_pop:
saveData(Constants.VALUE_POP);
Toast.makeText(this, resources.getString(R.string.message_popularity),Toast.LENGTH_LONG).show();
break;
case R.id.menu_top:
saveData(Constants.VALUE_TOP);
Toast.makeText(this, resources.getString(R.string.message_rating),Toast.LENGTH_LONG).show();
break;
}
return super.onOptionsItemSelected(item);
}
#Override
protected void onPause() {
super.onPause();
Parcelable recyclerViewState;
recyclerViewState = recyclerView.getLayoutManager().onSaveInstanceState();//save
recyclerView.getLayoutManager().onRestoreInstanceState(recyclerViewState);
}
#Override
protected void onPostResume() {
super.onPostResume();
Parcelable recyclerViewState;
recyclerViewState = recyclerView.getLayoutManager().onSaveInstanceState();//save
recyclerView.getLayoutManager().onRestoreInstanceState(recyclerViewState);
}
#SuppressLint("StaticFieldLeak")
#Override
public Loader<String> onCreateLoader(int id, final Bundle args) {
return new AsyncTaskLoader<String>(this) {
#Override
protected void onStartLoading() {
super.onStartLoading();
forceLoad();
progressBar.setVisibility(View.VISIBLE);
errorTextView.setVisibility(View.INVISIBLE);
}
#Override
public void deliverResult(String data) {
super.deliverResult(data);
}
#Override
public String loadInBackground() {
String jsonString = "";
URL url = NetworkUtils.buildUrl(args.getString(Constants.LOADER_MOVIES_EXTRA));
try {
jsonString += NetworkUtils.getResponseFromHttpUrl(url);
} catch (IOException e) {
e.printStackTrace();
}
if(jsonString.isEmpty()){
} else {
try {
JSONObject jsonObject = new JSONObject(jsonString);
JSONArray jsonArray = jsonObject.getJSONArray(Constants.JSON_KEY_MOVIE_RESULTS);
for (int i = 0; i < jsonArray.length(); i++) {
//Get 1 movie from JSON
String mTitle;
int mId;
String mPosterUrl;
String mPlot;
double mUserRating;
String mReleaseDate;
JSONObject Jmovie = (JSONObject) jsonArray.get(i);
mTitle = Jmovie.getString(Constants.JSON_KEY_MOVIE_TITLE);
mId = Jmovie.getInt(Constants.JSON_KEY_MOVIE_ID);
mPosterUrl = NetworkUtils.getPosterString(Jmovie.getString(Constants.JSON_KEY_MOVIE_POSTER_PATH));
mPlot = Jmovie.getString(Constants.JSON_KEY_MOVIE_OVERVIEW);
mUserRating = Jmovie.getDouble(Constants.JSON_KEY_MOVIE_VOTE_AVERAGE);
mReleaseDate = Jmovie.getString(Constants.JSON_KEY_MOVIE_RELEASE_DATE);
//Get videos
ArrayList<Video> mVideos = new ArrayList<Video>();
URL videosURL = NetworkUtils.buildUrlVideos(String.valueOf(mId));
String videosJSON = NetworkUtils.getResponseFromHttpUrl(videosURL);
JSONObject jsonObjectVideos = new JSONObject(videosJSON);
JSONArray jsonArrayVideos = jsonObjectVideos.getJSONArray(Constants.JSON_KEY_VIDEO_RESULTS);
if(jsonArrayVideos.length()==0){
mVideos = null;
} else {
for(int v = 0; v < jsonArrayVideos.length(); v++){
JSONObject Jvideo = (JSONObject) jsonArrayVideos.get(v);
String mVideoName;
String mVideoUrlString;
mVideoName = Jvideo.getString(Constants.JSON_KEY_VIDEO_NAME);
mVideoUrlString = "https://www.youtube.com/watch?v="+Jvideo.getString(Constants.JSON_KEY_VIDEO_KEY);
Video video = new Video(mVideoName, mVideoUrlString);
mVideos.add(video);
}
}
//GetReviews
ArrayList<Review> mReviews = new ArrayList<Review>();
URL reviewsURL = NetworkUtils.buildUrlReviews(String.valueOf(mId));
String reviewsJSON = NetworkUtils.getResponseFromHttpUrl(reviewsURL);
JSONObject jsonObjectReviews = new JSONObject(reviewsJSON);
JSONArray jsonArrayReviews = jsonObjectReviews.getJSONArray(Constants.JSON_KEY_REVIEW_RESULTS);
if(jsonArrayReviews.length()!=0) {
for(int r = 0; r < jsonArrayReviews.length(); r++){
JSONObject Jreview = (JSONObject) jsonArrayReviews.get(r);
String mReviewName;
String mReviewText;
mReviewName = Jreview.getString(Constants.JSON_KEY_REVIEW_AUTHOR);
mReviewText = Jreview.getString(Constants.JSON_KEY_REVIEW_CONTENT);
Review review = new Review(mReviewName, mReviewText);
mReviews.add(review);
}
}
Movie movie = new Movie(mTitle, mId, mPosterUrl, mPlot, mUserRating, mReleaseDate, mVideos, mReviews);
mMoviesCollection.add(movie);
}
} catch (JSONException e) {
e.printStackTrace();
} catch (IOException e){
e.printStackTrace();
}
}
return null;
}
};
}
#Override
public void onLoadFinished(Loader<String> loader, String data) {
progressBar.setVisibility(View.GONE);
mAdapter.notifyDataSetChanged();
}
#Override
public void onLoaderReset(Loader<String> loader) {
}
}

Because you are new to Android there is a lot wrong. So, many people probably won't want to chime in. Regardless, I'm new as well and in the same class as you are right now, so I'll give it a shot.
First, your loader is not returning the correct data type. Your loader should be of Loader<List<Movie>> and it should return a new AsyncTaskLoader<List<Movie>>. The reason you want this is to make use of everything the AsyncTaskLoader has to offer. I'll explain further.
Second, we'll cache the data inside the loader by moving the initial reference from the Activity into the loader.
So move private ArrayList<Movie> mMoviesCollection; as an instance variable of your AsyncTaskLoader. Remove the line mMoviesCollection = new ArrayList<Movie>(); from both your onCreate and initialize methods.
In your AsyncTaskLoader, you need to check if your data exists already in your onStartLoading before forceLoad and implement deliverResult.
So, your onStartLoading() should look like this:
#Override
protected void onStartLoading() {
super.onStartLoading();
if(mMoviesCollection.isEmpty()){
forceLoad();
progressBar.setVisibility(View.VISIBLE);
errorTextView.setVisibility(View.INVISIBLE);
} else {
deliverResult(mMoviesCollection)
}
}
And your deliverResult should look like this:
#Override
public void deliverResult(List<Movie> data) {
mMoviesCollection = data;
super.deliverResult(data);
}
Now you need to implement a setData(List<Movie> movies) method that sets your adapter's data instance variable and calls notifyDataSetChanged() in your Adapter. Like so:
public void setData(List<Movie> movies){
mMovies = movies;
notifyDataSetChanged();
}
Get rid of the List<Movie> from your adapter's constructor. This way you can construct the adapter without any data. The adapter's getItemCount() should return 0 if the data is null and the recyclerView will not try to build the view.
With that done you can then call onLoadFinished like this:
#Override
public void onLoadFinished(Loader<List<Movie>> loader, List<Movie> data) {
progressBar.setVisibility(View.GONE);
mAdapter.setData(data);
}
EDIT: Made a correction to account for the ArrayList instantiating as an Instance variable. You can either not instantiate the mMoviesCollection there and then do so later or just check if its empty with mMoviesCollection.isEmpty() as I changed above in onStartLoading.:
EDIT:
You need to get your libraries straight, you are using android.app in some places and android.support in others.
So in your imports change these:
import android.app.LoaderManager;
import android.content.AsyncTaskLoader;
import android.content.Loader;
all to:
import android.support.v4.app.LoaderManager;
import android.support.v4.content.AsyncTaskLoader;
import android.support.v4.content.Loader;
Now the TMDB.org API has a request limit of 40 requests per 10 seconds.
https://developers.themoviedb.org/3/getting-started/request-rate-limiting
Because of this, your Loader is not even completing everything and is throwing an exception. I would suggest breaking up when you call the videos and reviews into the MovieActivity by creating another AsyncTaskLoader there and calling each when the details screen loads.
You could also technically add a Thread.sleep(300) or less to your AsyncTaskLoader but it makes it seriously slow. In other words, you would have to push the data beyond the 10-second mark to load completely.
Now, with that and the changes we have made, everything does survive config changes such as screen rotation.
If you want the data to survive any further you will have to persist the data somehow. Like saving the json response as a string in onSaveInstanceState or saving the JSon String to the database you created.