RecyclerView throwing NullPointerException

Question

My recycler view is throwing java.lang.NullPointerException:

Attempt to invoke virtual method 'java.util.ArrayList com.msit.example.bunty.regform.entities.DataStore.getDataStore()' on a null object reference at com.msit.example.bunty.regform.adapters.MyRecyclerAdapter.getItemCount(MyRecyclerAdapter.java:65)

MyRecyclerAdapter.java

package com.msit.example.bunty.regform.adapters; import android.content.Context; import android.support.v7.widget.CardView; import android.support.v7.widget.RecyclerView; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.Button; import android.widget.TextView; import android.R.*; import android.support.v7.widget.LinearLayoutManager; import android.support.v7.widget.RecyclerView; import android.widget.Toast; import com.msit.example.bunty.regform.R; import com.msit.example.bunty.regform.entities.DataStore; import com.msit.example.bunty.regform.entities.UserData; import org.w3c.dom.Text; import java.lang.reflect.Array; import java.util.ArrayList; import java.util.List; /**l * Created by bunty on 1/5/16. */ public class MyRecyclerAdapter extends RecyclerView.Adapter<MyRecyclerAdapter.ViewHolder> { DataStore userDataStore=new DataStore(); //ArrayList<UserData> userDataStore=new ArrayList<UserData>(); public MyRecyclerAdapter(DataStore userDataStore) { this.userDataStore=userDataStore; } @Override public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { View view=LayoutInflater.from(parent.getContext()).inflate(R.layout.card_view,parent,false); ViewHolder viewHolder=new ViewHolder(view); return viewHolder; } @Override public void onBindViewHolder(ViewHolder holder, int position) { holder.fNameView.setText(userDataStore.getDataStore().get(position).getFirstName()); holder.lNameView.setText(userDataStore.getDataStore().get(position).getLastName()); holder.addressView.setText(userDataStore.getDataStore().get(position).getAddress()); holder.cityView.setText(userDataStore.getDataStore().get(position).getCity()); final String city=userDataStore.getDataStore().get(position).city; holder.cityView.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Toast.makeText(v.getContext(),city,Toast.LENGTH_SHORT).show(); } }); } @Override public int getItemCount() { if(!userDataStore.getDataStore().isEmpty()&&userDataStore.getDataStore()!=null) { return userDataStore.getDataStore().size(); } else { return 0; } } public static class ViewHolder extends RecyclerView.ViewHolder { TextView fNameView; TextView lNameView; TextView addressView; Button cityView; CardView cardView; public ViewHolder(View itemLayoutView) { super(itemLayoutView); fNameView = (TextView) itemView.findViewById(R.id.fn_view); lNameView = (TextView) itemView.findViewById(R.id.ln_view); addressView = (TextView) itemView.findViewById(R.id.addr_view); cityView=(Button)itemView.findViewById(R.id.city_view); cardView = (CardView) itemLayoutView.findViewById(R.id.card_list); } } }

I have two buttons Save and show_details,The app crashes when i click show_details if there are no values saved initially and raises an exception in getitemcount() method.

Before trying to see if it's empty or getDataStore, you should see if userDataStore in not null — wnieves19
– wnieves19, Commented Jan 8, 2016 at 20:06

wnieves19 · Accepted Answer · 2016-01-08 20:10:22Z

Fix getItemCount method like this

@Override public int getItemCount() { if(userDataStore == null){return 0;} if(!userDataStore.getDataStore().isEmpty()&&userDataStore.getDataStore()!=null) { return userDataStore.getDataStore().size(); } else{ return 0; } }

Gabriele Mariotti · Accepted Answer · 2016-01-08 20:59:56Z

You are initializing the userDataStore in your class, but you assign a new value in the constructor. In this way this variable can be null.

DataStore userDataStore=new DataStore(); public MyRecyclerAdapter(DataStore userDataStore) { this.userDataStore=userDataStore; }

You should check in your code if it is not null before using it.

In your getItemCount you can have a NPE, due to this reason.

 @Override public int getItemCount() { if(userDataStore != null && !userDataStore.getDataStore().isEmpty() && userDataStore.getDataStore()!=null) { return userDataStore.getDataStore().size(); } else{ return 0; } }

Kostas Drak · Accepted Answer · 2016-01-08 21:34:37Z

You initialize the Datastore in the Adapter and then in the constructor the param is a DataStore which means that you are already passing a newly created DataStore in the Activity that you are calling your Adapter. So just simplify your code:

DataStore userDataStore; public MyRecyclerAdapter(DataStore userDataStore){ this.userDataStore=userDataStore; } @Override public int getItemCount() { return userDataStore.getDataStore().size(); }

Hope it helps!!!

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