I am trying to implement RecyclerView with CardView. However, as I am loading my data from cloud, I need to use notifyDataSetChanged() method to update the view, However doing so causes NullPointerException in my custom Adapter class.
Here is how I am doing it in the main Activity:
public class BigBoard extends ActionBarActivity { private List<Person> persons; private RecyclerView rv; RVAdapter adapter; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); Parse.initialize(this, "app-id", "client-key"); setContentView(R.layout.activity_big_board); adapter = new RVAdapter(persons); rv=(RecyclerView)findViewById(R.id.rv); LinearLayoutManager llm = new LinearLayoutManager(this); rv.setLayoutManager(llm); rv.setHasFixedSize(true); initializeData(); initializeAdapter(); } private void initializeData(){ persons = new ArrayList<>(); ParseQuery<ParseObject> query = new ParseQuery<ParseObject>("Credentials"); query.findInBackground(new FindCallback<ParseObject>() { public void done(List<ParseObject> credentialList, ParseException e) { if (e == null) { for(int i=0;i<credentialList.size();i++) { persons.add(new Person(credentialList.get(i).getString("Name"), credentialList.get(i).getString("SurName"))); Log.d("OUT", "So the Val::------> " + persons); adapter.notifyDataSetChanged();// <---- Problem line } } else { Log.d("score", "Error: " + e.getMessage()); } } }); } private void initializeAdapter(){ rv.setAdapter(adapter); } And here is the code to the Adapter class:
public class RVAdapter extends RecyclerView.Adapter<RVAdapter.PersonViewHolder> { public static class PersonViewHolder extends RecyclerView.ViewHolder { CardView cv; TextView personName; TextView personAge; //ImageView personPhoto; PersonViewHolder(View itemView) { super(itemView); cv = (CardView)itemView.findViewById(R.id.cv); personName = (TextView)itemView.findViewById(R.id.person_name); personAge = (TextView)itemView.findViewById(R.id.person_age); //personPhoto = (ImageView)itemView.findViewById(R.id.person_photo); } } List<Person> persons; RVAdapter(List<Person> persons){ this.persons = persons; } @Override public void onAttachedToRecyclerView(RecyclerView recyclerView) { super.onAttachedToRecyclerView(recyclerView); } @Override public PersonViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) { View v = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.item, viewGroup, false); PersonViewHolder pvh = new PersonViewHolder(v); return pvh; } @Override public void onBindViewHolder(PersonViewHolder personViewHolder, int i) { personViewHolder.personName.setText(persons.get(i).name); personViewHolder.personAge.setText(persons.get(i).surname); // personViewHolder.personPhoto.setImageResource(persons.get(i).photoId); } @Override public int getItemCount() { return persons.size(); } And I believe return persons.size(); this is the line that causes NullPointerException each time I call notifyDataSetChanged() as I guess this is empty or so! The question is how to fix this?
here is the logcat as well:
> java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference at obx.com.futurister.RVAdapter.getItemCount(RVAdapter.java:58) at android.support.v7.widget.RecyclerView.onMeasure(RecyclerView.java:2357) at android.view.View.measure(View.java:18788) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951) at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465) at android.widget.LinearLayout.measureHorizontal(LinearLayout.java:1112) at android.widget.LinearLayout.onMeasure(LinearLayout.java:632) at android.view.View.measure(View.java:18788) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951) at android.widget.FrameLayout.onMeasure(FrameLayout.java:194) at android.support.v7.internal.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:124) at android.view.View.measure(View.java:18788) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951) at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465) at android.widget.LinearLayout.measureVertical(LinearLayout.java:748) at android.widget.LinearLayout.onMeasure(LinearLayout.java:630) at android.view.View.measure(View.java:18788) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951) at android.widget.FrameLayout.onMeasure(FrameLayout.java:194) at android.view.View.measure(View.java:18788) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951) at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465) at android.widget.LinearLayout.measureVertical(LinearLayout.java:748) at android.widget.LinearLayout.onMeasure(LinearLayout.java:630) at android.view.View.measure(View.java:18788) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951) at android.widget.FrameLayout.onMeasure(FrameLayout.java:194) at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2643) at android.view.View.measure(View.java:18788) at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2100) at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1216) at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1452) at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1107) at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6013) at android.view.Choreographer$CallbackRecord.run(Choreographer.java:858) at android.view.Choreographer.doCallbacks(Choreographer.java:670) at android.view.Choreographer.doFrame(Choreographer.java:606) at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844) at android.os.Handler.handleCallback(Handler.java:739) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:148) at android.app.ActivityThread.main(ActivityThread.java:5417) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
