RecyclerView中的getItemcount上的空指针异常

Question

I have been working on recyclerView but when i run my app it is not showing any data on the activity and app crashes and it give error on this method

Here is my Adaptor class:

public class Adaptor extends RecyclerView.Adapter<Adaptor.ViewHolder> {


private  ArrayList<info> Info=new ArrayList<>();

public Adaptor(ArrayList<info> info) {
    this.Info = info;
}


public void updateList(ArrayList<info> data) {
    Info = data;
    notifyDataSetChanged();
}

@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {


    View itemView = LayoutInflater.from(parent.getContext())
            .inflate(R.layout.list_view, parent, false);

         return new ViewHolder(itemView);


}



@Override
public void onBindViewHolder(ViewHolder holder, int position)
{

    info i= Info.get(position);
    holder.name.setText(i.getName());
    holder.city.setText(i.getCity());
    holder.city.setText(i.getUniversity());


}



public class ViewHolder extends RecyclerView.ViewHolder {

    TextView name, city, uni;


    public ViewHolder(final View v) {
        super(v);
        name = (TextView) v.findViewById(R.id.name);
        city = (TextView) v.findViewById(R.id.city);
        uni = (TextView) v.findViewById(R.id.university);

    }




}

public int getItemCount() {
    return Info.size();
}

}

Here is my activity class:

    public class Home extends AppCompatActivity implements HomeCallBack {

    public ArrayList<info> Info;
    private  Adaptor myadaptor;
private RecyclerView recyclerView;
private RecyclerView.LayoutManager layoutManager;



@Override
 protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_home);

    recyclerView=(RecyclerView)findViewById(R.id.recycle_view);
      Info=new ArrayList<>();

    myadaptor=new Adaptor(Info);
    recyclerView.addItemDecoration(new DividerItemDecoration(this, LinearLayoutManager.VERTICAL));
    LinearLayoutManager mLayoutManager = new LinearLayoutManager(getApplicationContext());
    recyclerView.setLayoutManager(mLayoutManager);
    recyclerView.setItemAnimator(new DefaultItemAnimator());
    recyclerView.setAdapter(myadaptor);



    BackgroundHome backgroundHome=new BackgroundHome(this,this);
    backgroundHome.execute();


}

@Override
public void processData(JSONArray data)
{

    JSONObject js;

            if(data!=null)
            {
                Info=new ArrayList<>();


                try
                {
                    for(int i=0;i<data.length();i++)
                    {
                        js =data.getJSONObject(i);
                        info in=new 


  info(js.getString("Names"),js.getString("city"),
  js.getString("university"));
                        Info.add( in);

                    }


                    myadaptor=new Adaptor(Info);

                    recyclerView.setAdapter(myadaptor);

                } catch (JSONException e) {
                    e.printStackTrace();
                }

                myadaptor.updateList(Info);


               }

Whenever i run it, it crashes and the error occur in getItemcount() method that it is null but i have initialize it to Info.size();

Answer 1

In your processData function, you're creating an Info list, adding new items to it. That's all good.

However, after that you're creating a new adapter with that Info list, then you're setting that adapter again with the Info list.

myadaptor =new Adaptor(Info);
recyclerView.setAdapter(myadaptor);

} catch (JSONException e) {
    e.printStackTrace();
}

myadaptor.updateList(Info);

Perhaps that's causing issues with it becoming null.

Answer 2

okey .. i checked your code. For me there is no obvious reason for this exception but anyway let us fix and debug some issues.

before anything please change the name of you objects/class ...

/// you have class with name 'info'
private  ArrayList<info> Info=new ArrayList<>();
// here you set variable with the same class name !!! 
public Adaptor(ArrayList<info> info) {
  this.Info = info;
}

And test your program if the problem is still then let use test your project.

Firstly in your adapter replace this line private ArrayList<info> Info=new ArrayList<>(); to private ArrayList<info> Info= null; .Then let us debug your code ..

Firstly set these lines as a comment BackgroundHome backgroundHome=new BackgroundHome(this,this); backgroundHome.execute(); BackgroundHome backgroundHome=new BackgroundHome(this,this); backgroundHome.execute(); then run your program .. Mostly your program is going to run without error .. if this happened then your error in processData(JSONArray data)

Then let us check your code and modify it. You do not need these lines .

 myadaptor=new Adaptor(Info); // delete

 recyclerView.setAdapter(myadaptor);// delete

Now run your program ..