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How Best To Implement ViewModel( in AndroidX) So Data Survives Configuration Changes

I am trying to implement a ViewModel architecture for a RecyclerView in AndroidX, following the example as stated in enter link description here and enter link description here. Items in the recyclerView get selected on position clicked, but for some reason, the selected item de-select and revert to default after the device is rotated and configuration changed. I know there have been answers for questions like this in the past, but all I have seen are either not directly applicable in my case or are simply for deprecated cases.
CAN SOMEONE PLEASE TELL ME WHAT I AM DOING WRONG!
Below are snippets from my Code:
Dependencies added
dependencies {
def lifecycle_version = "2.2.0"
// ViewModel
implementation "androidx.lifecycle:lifecycle-viewmodel:$lifecycle_version"
// LiveData
implementation "androidx.lifecycle:lifecycle-livedata:$lifecycle_version"
// Saved state module for ViewModel
implementation "androidx.lifecycle:lifecycle-viewmodel-savedstate:$lifecycle_version"
// Annotation processor
annotationProcessor "androidx.lifecycle:lifecycle-compiler:$lifecycle_version"
implementation 'androidx.hilt:hilt-lifecycle-viewmodel:1.0.0-alpha02'
}
Repository Class:
public class TopicRepository {
private Application application;
private SharedPreferences sharedPreferences;
private ArrayList<RootTopic> topicGroupList;
private MutableLiveData<ArrayList<RootTopic>>topicGroupMLD;
public TopicRepository(Application application) {
this.application = application;
}
public LiveData<ArrayList<RootTopic>> getRootTopicLD(String subject){
if (topicGroupMLD == null){
topicGroupMLD = new MutableLiveData<ArrayList<RootTopic>>();
generateTopicGroup(subject);
}
return topicGroupMLD;
}
private void generateTopicGroup(final String subject){
Log.d(TAG, "generateTopicGroup: CALLED");
isRequestingMLD.postValue(true);
final String subjectTopicGroupList = subject + "TopicGroupList";
sharedPreferences = application.getSharedPreferences(AppConstant.Constants.PACKAGE_NAME, Context.MODE_PRIVATE);
String serializedTopicGroup = sharedPreferences.getString(subjectTopicGroupList, null);
if (serializedTopicGroup != null){
Gson gson = new Gson();
Type type = new TypeToken<ArrayList<RootTopic>>(){}.getType();
topicGroupList = gson.fromJson(serializedTopicGroup, type);
topicGroupMLD.postValue(topicGroupList);
}else {// - Not saved in SP
Log.d(TAG, "getTopicGroup: NOT IN SP");
new ActiveConnectionCheck(new ActiveConnectionCheck.Consumer() {
#Override
public void accept(Boolean internet) {
Log.d(TAG, "accept: CHECKED INTERNET");
if (internet){
Log.d(TAG, "accept: INTERNET CONNECTION = TRUE");
internetCheckMLD.postValue(AppConstant.Constants.IS_INTERNET_REQUEST_SUCCESS);
FirebaseFirestore fbFStore = FirebaseFirestore.getInstance();
CollectionReference lectureRef = fbFStore.collection(subject);
lectureRef.orderBy(AppConstant.Constants.POSITION, Query.Direction.ASCENDING)
.get().addOnSuccessListener(
new OnSuccessListener<QuerySnapshot>() {
#Override
public void onSuccess(QuerySnapshot queryDocumentSnapshots) {
ArrayList<Topic>topicList = new ArrayList<>();
ArrayList<String> rootTitleList = new ArrayList<>();
for (QueryDocumentSnapshot snapshot : queryDocumentSnapshots){
Topic topic = snapshot.toObject(Topic.class);
topicList.add(topic);
}
Log.d(TAG, "onSuccess: TopicListSize = " + topicList.size());
for (Topic topic : topicList){
String rootTopicString = topic.getRootTopic();
if (!rootTitleList.contains(rootTopicString)){
rootTitleList.add(rootTopicString);
}
}
Log.d(TAG, "onSuccess: RootTitleListSize = " + rootTitleList.size());
for (int x = 0; x < rootTitleList.size(); x ++){
RootTopic rootTopic = new RootTopic(rootTitleList.get(x), new ArrayList<Topic>());
topicGroupList = new ArrayList<>();
topicGroupList.add(rootTopic);
}
for (int e = 0; e < topicList.size(); e++){
addTopicToGroup(topicGroupList, topicList.get(e));
}
topicGroupMLD.postValue(topicGroupList);
Gson gson = new Gson();
String serializedTopicGroup = gson.toJson(topicGroupList);
sharedPreferences.edit().putString(subjectTopicGroupList, serializedTopicGroup).apply();
Log.d(TAG, "onSuccess: TOPICGROUPSIZE = " + topicGroupList.size());
Log.d(TAG, "onSuccess: SERIALIZED GROUP = " + serializedTopicGroup);
isRequestingMLD.postValue(false);
}
}
).addOnFailureListener(
new OnFailureListener() {
#Override
public void onFailure(#NonNull Exception e) {
isRequestingMLD.postValue(false);
Log.d(TAG, "onFailure: FAILED TO GET TOPICLIST e = " + e.toString());
}
}
);
}else {
internetCheckMLD.postValue(AppConstant.Constants.IS_INTERNET_REQUEST_FAIL);
Log.d(TAG, "accept: InternetCONECTION = " + false);
}
}
});
}
}
private void addTopicToGroup(ArrayList<RootTopic>rootGroup, Topic topic){
for (int x = 0; x < rootGroup.size(); x++){
RootTopic rootTopic = rootGroup.get(x);
if (rootTopic.getRootTopicName().equals(topic.getRootTopic())){
rootTopic.getTopicGroup().add(topic);
}
}
}
}
My ViewModel class
public class LectureViewModel extends AndroidViewModel {
public static final String TAG = AppConstant.Constants.GEN_TAG + ":LectureVM";
private Application application;
private TopicRepository topicRepository;
private ArrayList<RootTopic> topicGroupList;
public LectureViewModel(#NonNull Application application) {
super(application);
this.application = application;
topicRepository = new TopicRepository(application);
}
public LiveData<ArrayList<RootTopic>> getRootTopicListLD(String subject){
return topicRepository.getRootTopicLD(subject);
}
}
Activity Implementing ViewModel
public class LectureRoomActivity extends AppCompatActivity {
public static final String TAG = AppConstant.Constants.GEN_TAG + " LecRoom";
private LectureViewModel lectureRoomVM;
private String subject;
private RecyclerView mainRecyclerView;
private RootTopicAdapter rootTopicAdapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_lecture_room);
Intent intent = getIntent();
subject = intent.getStringExtra(AppConstant.Constants.SUBJECT);
mainRecyclerView = findViewById(R.id.recyclerView);
downloadVM = new ViewModelProvider(this).get(DownloadLectureViewModel.class);
lectureRoomVM = new ViewModelProvider(this).get(LectureViewModel.class);
lectureRoomVM.getRootTopicListLD(subject).observe(
this,
new Observer<ArrayList<RootTopic>>() {
#Override
public void onChanged(ArrayList<RootTopic> rootTopics) {
if (rootTopics != null){
currentTopic = lectureRoomVM.getCursorTopic(subject, rootTopics);
setUpRec(rootTopics, currentTopic);
}
}
});
}
private void setUpRec( ArrayList<RootTopic>topicGroup, CursorTopic currentTopic){
rootTopicAdapter = new RootTopicAdapter(topicGroup,
new ArrayList<String>(), currentTopic.getParentPosition(),
currentTopic.getCursorPosition());
LinearLayoutManager linearLayoutManager = new LinearLayoutManager(
this, RecyclerView.VERTICAL,false);
mainRecyclerView.setHasFixedSize(true);
mainRecyclerView.setLayoutManager(linearLayoutManager);
mainRecyclerView.setAdapter(rootTopicAdapter);
Log.d(TAG, "setUpRec: SETTING REC");
}
}

For saving and restoring UI related data you better use savedInstanceState Bundle to survive the last state. To achive this you simply override two methods in you UI activity. See the sample code snippet below.
In your RootTopicAdapter
// Add this where you detect the item click, probably in your adaptor class
private int lastRecyclerViewIndex; // define the variable to hold the last index
...
#Override
public void onClick(View v) {
lastRecyclerViewIndex = getLayoutPosition();
}
public int getLastIndex() {
return lastRecyclerViewIndex;
}
In your view model class
public class LectureViewModel extends AndroidViewModel {
public static final String TAG = AppConstant.Constants.GEN_TAG + ":LectureVM";
private Application application;
private TopicRepository topicRepository;
private ArrayList<RootTopic> topicGroupList;
public boolean mustRestore; // Is there any data to restore
public int lasIndexSelected;
public LectureViewModel(#NonNull Application application) {
super(application);
this.application = application;
topicRepository = new TopicRepository(application);
}
public LiveData<ArrayList<RootTopic>> getRootTopicListLD(String subject){
return topicRepository.getRootTopicLD(subject);
}
}
In you UI activity which uses the RecyclerView
public class LectureRoomActivity extends AppCompatActivity {
...
private LectureViewModel lectureRoomVM;
...
private RecyclerView mainRecyclerView;
private RootTopicAdapter rootTopicAdapter;
...
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_lecture_room);
Intent intent = getIntent();
subject = intent.getStringExtra(AppConstant.Constants.SUBJECT);
mainRecyclerView = findViewById(R.id.recyclerView);
downloadVM = new ViewModelProvider(this).get(DownloadLectureViewModel.class);
lectureRoomVM = new ViewModelProvider(this).get(LectureViewModel.class);
lectureRoomVM.getRootTopicListLD(subject).observe(
this,
new Observer<ArrayList<RootTopic>>() {
#Override
public void onChanged(ArrayList<RootTopic> rootTopics) {
if (rootTopics != null){
currentTopic = lectureRoomVM.getCursorTopic(subject, rootTopics);
setUpRec(rootTopics, currentTopic);
// Exactly here, after setting up the data get your index for example
if(lectureRoomVM.mustRestore){
// Check the item count in the adaptor to avoid crashes
if(mainRecyclerView.getAdapter().getItemCount >= lastRecyclerViewIndex){
mainRecyclerView.findViewHolderForAdapterPosition(lastRecyclerViewIndex).itemView.performClick();
}
// After the restoration set the mustRestore to false
lectureRoomVM.mustRestore = false;
}
}
}
});
}
#Override
protected void onDestroy() {
super.onDestroy();
Log.d(E, "onDestroy");
/*
* Here just set the mustRestore to true in order to be able to restore in onCreate method.
* If the application itself is not destroyed your data will still be live in the
* memory thanks to the ViewModel's life cycle awarness.
*/
lectureRoomVM.mustRestore = true;
}
}
There you go. Try this logic carefully without bugs. Then I think you will achive what you want to get.

Retrieving data from Cloud Firestore with AsynkTaskLoader in Android

I'm new to Android and Firebase and I'm having this weird bug I don't understand. I have a RecyclerView that should display a list of Strings that have dates followed by a number. Now, I want to retrieve the data from Cloud Firestore and display it. For this purpose, I use an AsyncTaskLoader and in loadInBackground() I retrieve the data from Cloud Firestore. Now, when I start the activity, it shows the error message (and it will keep behaving this way no matter how many times I Hit the refresh button). However, if I turn off the screen and then turn it on, it shows the data the way I wish. The following is my code
public class MeasureListActivity extends AppCompatActivity implements
MeasuresAdapter.MeasuresAdapterOnClickHandler,
LoaderManager.LoaderCallbacks<String[]> {
private RecyclerView mRecyclerView;
private FirebaseAuth mAuth;
private MeasuresAdapter mMeasuresAdapter;
private TextView mErrorMessageDisplay;
private ProgressBar mLoadingIndicator;
private static final int MEASURES_LOADER_ID = 0;
#Override
public boolean onCreateOptionsMenu(Menu menu) {
/* Use AppCompatActivity's method getMenuInflater to get a handle on the menu inflater */
MenuInflater inflater = getMenuInflater();
/* Use the inflater's inflate method to inflate our menu layout to this menu */
inflater.inflate(R.menu.measures_list, menu);
/* Return true so that the menu is displayed in the Toolbar */
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.action_refresh) {
invalidateData();
getSupportLoaderManager().restartLoader(MEASURES_LOADER_ID, null, this);
return true;
}
return super.onOptionsItemSelected(item);
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_measure_list);
mAuth = FirebaseAuth.getInstance();
mRecyclerView = (RecyclerView) findViewById(R.id.recyclerview_measures);
mErrorMessageDisplay = (TextView) findViewById(R.id.tv_error_message_display);
LinearLayoutManager layoutManager
= new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false);
mRecyclerView.setLayoutManager(layoutManager);
mRecyclerView.setHasFixedSize(true);
mMeasuresAdapter = new MeasuresAdapter(this);
mRecyclerView.setAdapter(mMeasuresAdapter);
mLoadingIndicator = (ProgressBar) findViewById(R.id.pb_loading_indicator);
int loaderId = MEASURES_LOADER_ID;
LoaderManager.LoaderCallbacks<String[]> callback = MeasureListActivity.this;
Bundle bundleForLoader = null;
getSupportLoaderManager().initLoader(loaderId, bundleForLoader, callback);
}
#Override
public Loader<String[]> onCreateLoader(int id, final Bundle loaderArgs) {
return new AsyncTaskLoader<String[]>(this) {
String[] mWMeasuresData = null;
#Override
protected void onStartLoading() {
if (mWMeasuresData != null) {
deliverResult(mWMeasuresData);
} else {
mLoadingIndicator.setVisibility(View.VISIBLE);
forceLoad();
}
}
private String[] aux;
#Override
public String[] loadInBackground() {
FirebaseFirestore db = FirebaseFirestore.getInstance();
db.collection("medidas").whereEqualTo("id_user", "3Aq3g0czkarT8GIbyESV").get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
#Override
public void onComplete(#NonNull Task<QuerySnapshot> task) {
if (task.isSuccessful()) {
QuerySnapshot snapshot = task.getResult();
int tam = snapshot.getDocuments().size();
aux = new String[tam];
for (int i = 0; i < tam; i++) {
String temp = "";
DocumentSnapshot doc = snapshot.getDocuments().get(i);
temp += doc.get("fecha") + " ";
temp += doc.get("valor");
aux[i] = temp;
}
}
}
});
return aux;
}
public void deliverResult(String[] data) {
mWMeasuresData = data;
super.deliverResult(data);
}
};
}
#Override
public void onLoadFinished(Loader<String[]> loader, String[] data) {
mLoadingIndicator.setVisibility(View.INVISIBLE);
mMeasuresAdapter.setMeasuresData(data);
if (null == data) {
showErrorMessage();
} else {
showMeasuresDataView();
}
}
#Override
public void onLoaderReset(Loader<String[]> loader) {
}
private void invalidateData() {
mMeasuresAdapter.setMeasuresData(null);
}
private void showMeasuresDataView() {
/* First, make sure the error is invisible */
mErrorMessageDisplay.setVisibility(View.INVISIBLE);
/* Then, make sure the weather data is visible */
mRecyclerView.setVisibility(View.VISIBLE);
}
private void showErrorMessage() {
/* First, hide the currently visible data */
mRecyclerView.setVisibility(View.INVISIBLE);
/* Then, show the error */
mErrorMessageDisplay.setVisibility(View.VISIBLE);
}
#Override
public void onClick(String measure) {
Context context = this;
Class destinationClass = DetailMeasureActivity.class;
Intent intentToStartDetailActivity = new Intent(context, destinationClass);
intentToStartDetailActivity.putExtra(Intent.EXTRA_TEXT, measure);
startActivity(intentToStartDetailActivity);
}
}
Can you help me with this?...thanks in advance

First of all, I think that when you call this block of code:
mLoadingIndicator.setVisibility(View.VISIBLE);
forceLoad();
You should also hide the error message view.
Also, on a more serious note, you do not need AsyncTaskLoader to get your data from firestore, firebase firestore already handles background work for you.
To be able to understand fully where the problem is from, you need to understand you activity lifecycle and add logs to mark critical events that will help you to know which block of code is called at any point in time. So I will encourage you to add logs for when the data loading starts, finishes and when you are hiding a view or showing a view just to be sure that all methods are called and also add logs to your activity lifecycles.

How can I make sharedpreferences in Custom Adapter get the latest values of my ArrayList?

I use Volley in the onCreate of my Activity which gets a string on my server, then I convert this string to an arraylist,checkedContactsAsArrayList, and I pass it over to my custom adapter using sharedpreferences, which does stuff with the arraylist in the listview.
But the custom adapter keeps getting the previous arraylist in sharedpreferences, not the one I've just got from the server. The Volley call is too late or something - I can see in logcat the latest values are put after they are got, if you know what I mean.
For example:
VolleyCall 1 putString: 1,2,3
VolleyCall 2 putString: 4,5,6
VolleyCall 3 putString: 7,8,9
Custom Adapter 1 getString: gets values of the last time app was used
Custom Adapter 2 getString: 1,2,3
Custom Adapter 3 getString: 4,5,6
Any idea how to fix this? I could try doing the Volley call in the getView of my custom adapter but I've read on Stackoverflow that's bad practice.
Here are the relvant parts of my code - I've slimmed it down a bit, as there's a lot of stuff in there irrelevant to this issue.
Here's the code of my activity, ViewContact:
public class ViewContact extends AppCompatActivity implements android.widget.CompoundButton.OnCheckedChangeListener {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(activity_view_contact);
//selectPhoneContacts is an empty array list that will hold our SelectPhoneContact info
selectPhoneContacts = new ArrayList<SelectPhoneContact>();
listView = (ListView) findViewById(R.id.listviewPhoneContacts);
StringRequest stringRequest = new StringRequest(Request.Method.POST, ViewContact_URL,
new Response.Listener<String>() {
#Override
public void onResponse(String response) {
//toast the response of ViewContact.php, which has been converted to a
//JSON object by the Php file with JSON encode
Toast.makeText(ViewContact.this, "OnResponse is" + response, Toast.LENGTH_LONG).show();
System.out.println("ViewContact: And the response is " + response);
try {
//checkedContacts is a String
String checkedContacts = responseObject.getString("checkedcontacts");
//convert the checkedContacts string to an arraylist
checkedContactsAsArrayList = new ArrayList<String>(Arrays.asList(checkedcontacts.split(",")));
System.out.println("ViewContact: checkedContactsAsArrayList is " + checkedContactsAsArrayList);
//we want to bring the checkedContactsAsArrayList array list to our SelectPhoneContactAdapter.
// It looks like Shared Preferences
//only works easily with strings so best way to bring the array list in Shared Preferences is with
//Gson.
//Here, we PUT the arraylist into the sharedPreferences
SharedPreferences sharedPreferencescheckedContactsAsArrayList = PreferenceManager.getDefaultSharedPreferences(getApplication());
SharedPreferences.Editor editorcheckedContactsAsArrayList = sharedPreferencescheckedContactsAsArrayList.edit();
Gson gsoncheckedContactsAsArrayList = new Gson();
String jsoncheckedContactsAsArrayList = gsoncheckedContactsAsArrayList.toJson(checkedContactsAsArrayList);
editorcheckedContactsAsArrayList.putString("checkedContactsAsArrayList", jsoncheckedContactsAsArrayList);
editorcheckedContactsAsArrayList.commit();
System.out.println("ViewContact: jsoncheckedContactsAsArrayList is " + jsoncheckedContactsAsArrayList);
} catch (JSONException e) {
e.printStackTrace();
Toast.makeText(getApplicationContext(),
"Error: " + e.getMessage(),
Toast.LENGTH_LONG).show();
}
}
},
new Response.ErrorListener() {
#Override
public void onErrorResponse(VolleyError error) {
Toast.makeText(ViewContact.this, error.toString(), Toast.LENGTH_LONG).show();
}
}) {
#Override
protected Map<String, String> getParams() {
Map<String, String> params = new HashMap<String, String>();
//we are posting review_id into our ViewContact.php file, which
//we get when a row is clicked in populistolistview
//to get matching details
params.put("review_id", review_id);
return params;
}
};
RequestQueue requestQueue = Volley.newRequestQueue(this);
requestQueue.add(stringRequest);
#Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
//checkBoxforContact.setChecked(true);
}
//******for the phone contacts in the listview
// Load data in background
class LoadContact extends AsyncTask<Void, Void, Void> {
#Override
protected void onPreExecute() {
super.onPreExecute();
}
#Override
protected Void doInBackground(Void... voids) {
//we want to delete the old selectContacts from the listview when the Activity loads
//because it may need to be updated and we want the user to see the updated listview,
//like if the user adds new names and numbers to their phone contacts.
selectPhoneContacts.clear();
SelectPhoneContact selectContact = new SelectPhoneContact();
selectContact.setName(phoneNameofContact);
}
return null;
}
#Override
protected void onPostExecute(Void aVoid) {
super.onPostExecute(aVoid);
adapter = new SelectPhoneContactAdapter(selectPhoneContacts, ViewContact.this,0);
listView.setAdapter(adapter);
adapter.notifyDataSetChanged();
}
}
#Override
protected void onResume() {
super.onResume();
// getPrefs();
ViewContact.LoadContact loadContact = new ViewContact.LoadContact();
loadContact.execute();
Toast.makeText(ViewContact.this, "resuming!", Toast.LENGTH_SHORT).show();
}
}
And my custom adapter, SelectPhoneContactAdapter :
public class SelectPhoneContactAdapter extends BaseAdapter {
//define a list made out of SelectPhoneContacts and call it theContactsList
public List<SelectPhoneContact> theContactsList;
//define an array list made out of SelectContacts and call it arraylist
private ArrayList<SelectPhoneContact> arraylist;
Context _c;
ArrayList<String> MatchingContactsAsArrayList;
ArrayList<String> checkedContactsAsArrayList;
ArrayList <String> allNamesofContacts;
String contactToCheck;
//we will run through different logic in this custom adapter based on the activity that is passed to it
private int whichactivity;
String phoneNumberofContact;
String[] phoneNumberofContactStringArray;
String ContactsString;
Intent intent;
public SelectPhoneContactAdapter(final List<SelectPhoneContact> selectPhoneContacts, Context context, int activity) {
theContactsList = selectPhoneContacts;
_c = context;
this.arraylist = new ArrayList<SelectPhoneContact>();
this.arraylist.addAll(theContactsList);
whichactivity = activity;
//we are fetching the array list checkedContactsAsArrayList, created in ViewContact.
//with this we will put a tick in the checkboxes of contacts the review is being shared with
SharedPreferences sharedPreferencescheckedContactsAsArrayList = PreferenceManager.getDefaultSharedPreferences(_c);
Gson gsoncheckedContactsAsArrayList = new Gson();
String jsoncheckedContactsAsArrayList = sharedPreferencescheckedContactsAsArrayList.getString("checkedContactsAsArrayList", "");
Type type2 = new TypeToken<ArrayList<String>>() {
}.getType();
checkedContactsAsArrayList = gsoncheckedContactsAsArrayList.fromJson(jsoncheckedContactsAsArrayList, type2);
System.out.println("SelectPhoneContactAdapter checkedContactsAsArrayList :" + checkedContactsAsArrayList);
}
}
#Override
public int getCount() {
return arraylist.size();
}
#Override
public Object getItem(int i) {
return arraylist.get(i);
}
#Override
public long getItemId(int i) {
return i;
}
static class ViewHolder {
//In each cell in the listview show the items you want to have
//Having a ViewHolder caches our ids, instead of having to call and load each one again and again
TextView title, phone;
CheckBox check;
Button invite;
}
#Override
public View getView(final int i, View convertView, ViewGroup viewGroup) {
//this is the SelectPhoneContact object; consists of textboxes, buttons, checkbox
final SelectPhoneContact data = (SelectPhoneContact) arraylist.get(i);
ViewHolder holder = null;
if (convertView == null) {
//if there is nothing there (if it's null) inflate the view with the layout
LayoutInflater li = (LayoutInflater) _c.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = li.inflate(R.layout.phone_inflate_listview, null);
holder = new ViewHolder();
//So, for example, title is cast to the name id, in phone_inflate_listview,
//phone is cast to the id called no etc
holder.title = (TextView) convertView.findViewById(R.id.name);
holder.phone = (TextView) convertView.findViewById(R.id.no);
holder.invite = (Button) convertView.findViewById(R.id.btnInvite);
holder.check = (CheckBox) convertView.findViewById(R.id.checkBoxContact);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
//in the listview for contacts, set the name
holder.title.setText(data.getName());
//in the listview for contacts, set the number
holder.phone.setText(data.getPhone());
holder.check.setTag(data);
return convertView;
}
}

Call this: loadContact.execute();
After you call .commit();
ViewContact.LoadContact loadContact = new ViewContact.LoadContact();
loadContact.execute();

How do I go about applying data I get from doInBackground() to apply to my RecyclerView?

I have viewed over 50 pages to find solution for my extremely simple app, but none seems to work for me. Please help.
Problem: I have a refresh button in the menu in MainActivity. When this is pressed, I want to execute my AsyncTask, then update ALL items in my RecyclerView.
Situation.
My app fetches data from API by OpenWeatherMap.org, then displays the data.
I have a MainActivity class (And my recyclerView resides in here.)
For recyclerView, I'm using RecyclerView.Adapter with GridViewManager.
I have a separate AsyncTask class.
So, what I have tried and did not work:
Method 1. Normal way. When refresh button selected, call my AsyncTask. In my PostExecute(), I am calling setter in the MainActivity
public void setWeatherData(String[] weatherData) {this.weatherData = weatherData;}
to assign the result array from doInBackGround method.
Then in MainActivity,
myAsyncTask.execute("43017,us");
recyclerView.recyclerView.getAdapter().notifyDataSetChanged();
But this causes notifyDataSetChanged(); to be called BEFORE member vairable array in MainActivity is updated from onPostExecute().
Method 2. Trying to update UI entirely from onPostExecute method in MyAsyncTask.class.
Well I know onPostExecute, even when it is written in different class, runs on the UI thread. So within the method, I did something like
MainActivity mainActivity = new MainActivity();
RecyclerView recyclerView = mainActivity.findViewById(R.id.recyclerView);
RecyclerView.Adapter adapter = recyclerView.getAdapter();
adapter.notifyDataSetChanged();
In this method, with logging, I've confirmed that onPostExecute successfully updates the member variable in the MainActivity, it's just that notifyDataSetChanged gets called TOO early, specifically before onPostExecute is complete in the background.
I hope to get an answer for this and was clear enough about my situation. I will post my MainActivity, Adapter and AsyncTask codes down below.
MainActivity.java:
public class MainActivity extends AppCompatActivity {
private String weatherData[] = {
"Today - Sunny",
"Tomorrow - Cloudy",
"Tuesday - Rainy",
"Wednesday - Sunny",
"Thursday - Sunny",
"Friday - Sunny",
"Saturday - Cloudy",
"Sunday - Rainy :/"
};
private RecyclerView recyclerView;
private mAdapter adapter;
private static final int SPAN_COUNT = 1;
private MyAsyncTask myAsyncTask = new MyAsyncTask();
private Context context;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
recyclerView = (RecyclerView)findViewById(R.id.recyclerview_weatherData);
setLayout(getApplicationContext());
adapter = new mAdapter(weatherData);
recyclerView.setAdapter(adapter);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater menuInflater = getMenuInflater();
menuInflater.inflate(R.menu.menu, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
switch (id){
case R.id.action_refresh:
Log.v("Menu", "Refresh button selected.");
//for now, take some random ZIP code
myAsyncTask.execute("43017,us");
recyclerView.getAdapter().notifyDataSetChanged();
adapter.refreshContents(weatherData);
for (int i = 0; i<weatherData.length; i++) {
Log.v("Refresh button", weatherData[i].toString());
}
}
return true;
}
public void setLayout(Context context) {
int scrollPosition = 0;
//make a GridLayoutManager with 2 columns
LinearLayoutManager mLayoutManager = new LinearLayoutManager(context);
//set the mLayoutManager to the one that I just created
recyclerView.setLayoutManager(mLayoutManager);
recyclerView.scrollToPosition(scrollPosition);
recyclerView.setLayoutManager(new GridLayoutManager(context, SPAN_COUNT));
//set the offset decoration definition to my layout
int middle_spacing = 30;
boolean includeEdge = true;
recyclerView.addItemDecoration(new ItemOffsetDecoration(SPAN_COUNT, middle_spacing, includeEdge));
}
public void setWeatherData(String[] weatherData) {
this.weatherData = weatherData;
}
public String[] getWeatherData() { return weatherData; }
}
MyAsyncTask.java:
public class MyAsyncTask extends AsyncTask<String,Void,String[]> {
public final static String OPEN_WEATHER_MAP_API_KEY = "bc607b72747aa672bf2ac9a5f3a5fc84";
String forecastJsonStr = null;
private String format = "json";
private String units = "metric";
private int numDays = 7;
private String data[] =null;
private RecyclerView recyclerView;
private MainActivity mainActivity;
private RecyclerView.Adapter adapter;
#Override
protected String[] doInBackground(String... params) {
if (params.length == 0) {
Log.v("AsyncTask", "No parameter is taken.");
return null;
}
HttpURLConnection urlConnection = null;
BufferedReader reader = null;
try {
final String FORECAST_BASE_URL = "http://api.openweathermap.org/data/2.5/forecast/daily?";
final String QUERY_PARAM = "q";
final String FORMAT_PARAM = "mode";
final String UNITS_PARAM = "units";
final String DAYS_PARAM = "cnt";
final String APPID_PARAM = "APPID";
Uri builtUri = Uri.parse(FORECAST_BASE_URL).buildUpon()
.appendQueryParameter(QUERY_PARAM, params[0])
.appendQueryParameter(FORMAT_PARAM, format)
.appendQueryParameter(UNITS_PARAM, units)
.appendQueryParameter(DAYS_PARAM, Integer.toString(numDays))
.appendQueryParameter(APPID_PARAM, OPEN_WEATHER_MAP_API_KEY)
.build();
URL url = new URL(builtUri.toString());
urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.setRequestMethod("GET");
urlConnection.connect();
InputStream inputStream = urlConnection.getInputStream();
StringBuffer buffer = new StringBuffer();
if (inputStream == null) {
return null;
}
reader = new BufferedReader(new InputStreamReader(inputStream));
String line;
while ((line = reader.readLine()) != null) {
buffer.append(line + "\n");
}
if (buffer.length() == 0) {
return null;
}
//put the buffer in String var forecastJsonStr
forecastJsonStr = buffer.toString();
Log.v("AsyncTask", forecastJsonStr.toString());
} catch (IOException e) {
return null;
} finally {
if (urlConnection != null) {
urlConnection.disconnect();
}
if (reader != null) {
try {
reader.close();
} catch (final IOException e) {
Log.e("Async", "Reader is null, something wrong.");
}
}
}
//Then put the string contents into an array
try {
ParseWeatherData parser = new ParseWeatherData();
data = parser.getWeatherDataFromJson(forecastJsonStr, numDays);
return data;
} catch (JSONException e) {
e.printStackTrace();
}
return data;
}
#Override
protected void onPostExecute(final String data[]) {
super.onPostExecute(data);
if (data != null) {
//this log works fine: the fetched data is successfully stored...
for (int i = 0; i<data.length; i++) {
Log.v("onPostExecute", data[i].toString());
}
//how do I pass this data to the main thread?
mainActivity = new MainActivity();
mainActivity.setWeatherData(data);
}
}
}
Finally, mAdapter.java:
public class mAdapter extends RecyclerView.Adapter<mAdapter.ViewHolder> {
private String data[];
public mAdapter(String data[]) {
this.data = data;
}
#Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View listView = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_single_list, parent, false);
return new ViewHolder(listView);
}
#Override
public void onBindViewHolder(ViewHolder holder, int position) {
holder.weather.setText(data[position]);
Log.v("BindView", "Item " + position + " set.");
}
#Override
public int getItemCount() {
if (data == null) {
Log.v("WeatherAdapter", "Oops, getting null in the adapter.");
return 0;
} else {
return data.length;
}
}
public void refreshContents(String data[]) {
this.data = null;
this.data = data;
notifyDataSetChanged();
}
public static class ViewHolder extends RecyclerView.ViewHolder {
TextView weather, day;
//currently ViewHolder is set as the TextView for logging
public ViewHolder(View v) {
super(v);
weather = (TextView) v.findViewById(R.id.test_text);
// Define click listener for the ViewHolder's View.
v.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Log.d(TAG, "Element " + getAdapterPosition() + " clicked.");
}
});
}
}
}
Thank you in advance!

First don't create new object of MainActivity in MyAsyncTask. Actually what's happening is AsyncTask runs on a new Thread so when you do
myAsyncTask.execute("43017,us");
recyclerView.getAdapter().notifyDataSetChanged();
adapter.refreshContents(weatherData);
then myAsyncTask runs in a different thread and the next lines start executing right before .execute without waiting for asynctask to finish and even if it waits for the asynctask to finish, creating a new object to update the data in MainActivity is not gonna work. So what you can do to update your list from onPostExecute method is pass your Activity to myAsyncTask from parameters. Don't initialize your myAsyncTask in the beginning, just remove the = new MyAsyncTask() from private MyAsyncTask myAsyncTask = new MyAsyncTask(); in MainActivity and now replace the lines in MainActivity with this:
Instead of this in your MainActivity
myAsyncTask.execute("43017,us");
recyclerView.getAdapter().notifyDataSetChanged();
adapter.refreshContents(weatherData);
for (int i = 0; i<weatherData.length; i++) {
Log.v("Refresh button", weatherData[i].toString());
}
Write this
myAsyncTask = new MyAsyncTask(this);
myAsyncTask.execute("43017,us");
and to refresh the contents you can make your adapter public so that you could call notifydatasetchanged from myAsyncTask itself but if you want to follow your code written after .execute then you can move it to a new method something like below
public void refreshList(){
recyclerView.getAdapter().notifyDataSetChanged();
adapter.refreshContents(weatherData);
for (int i = 0; i<weatherData.length; i++) {
Log.v("Refresh button", weatherData[i].toString());
}
}
and now what's left is getting context of your MainActivity in MyAsyncTask and refreshing your list in onPostExecute. So make changes like following:
Create a constructor of your MyAsyncTask
public class MyAsyncTask extends AsyncTask<String,Void,String[]> {
MainActivity mainActivity;
public MyAsyncTask(MainActivity mainActivity){
this.mainActivity = mainActivity;
}
Replace this in MyAsyncTask
mainActivity = new MainActivity();
mainActivity.setWeatherData(data);
With this
mainActivity.setWeatherData(data);
mainActivity.refreshList();
I din't tested it myself but i think this should solve your problem. You can try debugging this and see how it is working. And if you face any problems please comment down below.
Edit
Based on the comment by #Ganesh Patil you can create an interface for this solution as well. For the reference of using interface in AsyncTask you can follow this link:
https://stackoverflow.com/a/28958913/7071039
But to keep it simple i didn't used interface and just passed the context of MainActivity in the MyAsyncTask
Editing based on the comment
Dear PC HUB, firstly thank you so much for your very detailed answer.
All of your explanations made sense and I applied the codes. My app
now doesn't crash and all the data is properly passed / retrieved but
somehow mainActivity.refreshList() and
recyclerView.getAdapter().notifyDataSetChanged() is still not working.
Hence, my recyclerView still doesn't change the contents at all... I
am not sure of what to do. – Rikuto Echigoya
change your refreshList into this
public void refreshList(){
/* Check your Weather Data size in this method to find out weather your data is changing or not */
Log.d("Tag","SIZE OF WEATHER DATA : "+weatherData.length);
/* You already have the adapter object so you don't need to
get it using recyclerview.getAdapter. Just do it directly like this */
adapter.notifyDataSetChanged();
// Not changing this as this will not stop your list from refreshing :P
for (int i = 0; i<weatherData.length; i++) {
Log.v("Refresh button", weatherData[i].toString());
}
}
Also make sure that you've called mainActivity.setWeatherData(data); before mainActivity.refreshList(); in your MyAsyncTask.
If it still doesn't solve your problem then share your updated code so that we could see why your list is not getting updated :)

Data is not populating in list, Android

I am trying to populate fragment listview using async task,
But listvew is not populating. I am getting data in logs, And there is no error and exception in logs.
I am following this example
dynamic listview adding "Load more items" at the end of scroll
Here is code:-
public class HindiFragment extends Fragment {
// XML node keys
static final String KEY_SONG = "song"; // parent node
static final String KEY_ID = "id";
static final String KEY_TITLE = "title";
static final String KEY_ARTIST = "artist";
static final String KEY_DURATION = "duration";
static final String KEY_THUMB_URL = "thumb_url";
static final String KEY_VIDEO_URL = "video";
static final String KEY_UPLOAD_BY = "upload_by";
Context abc=null;
static int startIndex = 0;
private WeakReference<MyAsyncTask> asyncTaskWeakRef;
ListView list;
static LazyAdapter adapter;
JSONObject json;
static int offset = 10;
static ArrayList<HashMap<String, String>> songsList = new ArrayList<HashMap<String, String>>();
public static Context hindiFragment=null;
private static int catId=0;
static View rootView ;
public HindiFragment(){}
public HindiFragment(int position) {
// TODO Auto-generated constructor stub
catId=position;
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
//StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
//StrictMode.setThreadPolicy(policy);
rootView = inflater.inflate(R.layout.main, container, false);
// TextView tvLabel = (TextView)rootView.findViewById(R.id.txtLabel);
// tvLabel.setText("Hello"); try
hindiFragment=rootView.getContext();
try{
//Toast.makeText(hindiFragment, "catid is "+catId,
// Toast.LENGTH_LONG).show();
UserFunctions userFunction = new UserFunctions();
json=userFunction.getAndroidVersion();
JSONArray android_version_array = json.getJSONArray("version");
TextView tv = (TextView) rootView.findViewById(R.id.android_version);
//getting android version
for (int i = 0; i < android_version_array.length(); i++) {
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
JSONObject myObj = android_version_array.getJSONObject(i);
if(! myObj.getString("version").equalsIgnoreCase(String.valueOf(getString(R.string.android_version)))){
tv.setText( Html.fromHtml(myObj.getString("text")));
tv.setMovementMethod(LinkMovementMethod.getInstance());
}else
{
tv.setVisibility(View.GONE);
}
// adding each child node to HashMap key => value
}
startNewAsyncTask(this.getActivity());
return rootView;
}catch(Exception e){
e.printStackTrace();
}
return rootView;
}
public static void loadMore(int startIndex,int page,Activity myActivity){
try{
UserFunctions userFunction = new UserFunctions();
Log.e("page ",""+page);
int status=0;
JSONObject json;
json = userFunction.getChannelData(String.valueOf(catId),page);
if(json.has("video")){
JSONArray deletedtrs_array = json.getJSONArray("video");
for (int i = 0; i < deletedtrs_array.length(); i++) {
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
JSONObject myObj = deletedtrs_array.getJSONObject(i);
// adding each child node to HashMap key => value
map.put(KEY_ID, myObj.getString("uid"));
map.put(KEY_TITLE, myObj.getString("uid"));
map.put(KEY_ARTIST,myObj.getString("video"));
map.put(KEY_DURATION, myObj.getString("duration"));
map.put(KEY_THUMB_URL,myObj.getString("thumb_url"));
map.put(KEY_VIDEO_URL, myObj.getString("url"));
map.put(KEY_UPLOAD_BY,"By: "+ myObj.getString("upload_by"));
// adding HashList to ArrayList
//if(!songsList.contains(map))
{
songsList.add(map);
status=1;
}
}
}
//if(status==1)
{
//]list=(ListView)rootView.findViewById(R.id.list);
// Getting adapter by passing xml data ArrayList
// adapter=new LazyAdapter(myActivity, songsList);
// list.setAdapter(adapter);
// adapter.notifyDataSetChanged();
}
}catch(Exception e){
e.printStackTrace();
}
}
private void startNewAsyncTask(Activity act) {
MyAsyncTask asyncTask = new MyAsyncTask(act);
this.asyncTaskWeakRef = new WeakReference<MyAsyncTask >(asyncTask );
asyncTask.execute();
}
private static class MyAsyncTask extends AsyncTask<Void, Void, Void> {
private WeakReference<HindiFragment> fragmentWeakRef;
HindiFragment uindiFragment;
Activity myActivity;
private MyAsyncTask (Activity activity) {
this.fragmentWeakRef = new WeakReference<HindiFragment>(uindiFragment);
myActivity=activity;
}
#Override
protected Void doInBackground(Void... params) {
//Toast.makeText(hindiFragment, "helllo",
// Toast.LENGTH_LONG).show();
//TODO: your background code
Log.e("Now in background",offset+"");
loadMore(startIndex, offset,myActivity);
return null;
}
#Override
protected void onPostExecute(Void response) {
super.onPostExecute(response);
ListView list=(ListView)rootView.findViewById(R.id.list);
// Getting adapter by passing xml data ArrayList
adapter=new LazyAdapter(myActivity, songsList);
list.setAdapter(adapter);
adapter.notifyDataSetChanged();
Log.e("Ended here11 ","now endeded11");
if (this.fragmentWeakRef.get() != null) {
//TODO: treat the result
adapter.notifyDataSetChanged();
}
}
}
}

You are over-using weak reference. My guess is your async task or fragment is being garbage collected since you use them cyclically: you can verify this by seeing if weakReference.get() returns null.
In fact, you don't need WeakReference at all: just implement appropriate cancel logic that you can call from onPause onStop or onDestroy depending on how you want to handle repeated calls.
Also you shouldn't pass the context to your Async class: instead create an observer such as:
public interface Callback {
public void onAsyncDone(Arraylist<DataItem> listItems);
}
and if not cancelled,
#Override public void onPostExecute(Void v) {
if (!isCancelled()) {
Callback c = callbackReference.get();
if (c != null) c.onAsyncDone(getListItems());
}
}
where getListItems() returns whatever work is done in doInBackground. Here I use a weak reference for the callback (which you implement in your activity) since you seem to want to use one. But again, as long as you release the reference to the context if cancelled, you don't actually need one. The reason the activity is wrapped as the Callback is that the async task should only have one job: process the items and pass them along. Let your activity or controller change the UI with the new items.

I suspect the loadMore() method does not load up any data to object songsList into the adapter. Simply trace the reason why it is not. There's no way I can debug this without using debugger, the code flow is rather complicated with unusually tight references and, more so, with static access.
The suspected code for review:
protected void onPostExecute(Void response) {
super.onPostExecute(response);
ListView list=(ListView)rootView.findViewById(R.id.list);
// Getting adapter by passing xml data ArrayList
adapter=new LazyAdapter(myActivity, songsList);
list.setAdapter(adapter);
adapter.notifyDataSetChanged();
...
}
Note: You can put some good logging in LazyAdapter code and see if data is populated there.