RecyclerView on a null object reference

Question

I've been trying to get data on the RecycleView for a day now, but it doesn't work. An error comes out:

E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.tokenauth, PID: 8011 java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.recyclerview.widget.RecyclerView.setAdapter(androidx.recyclerview.widget.RecyclerView$Adapter)' on a null object reference at com.example.tokenauth.Home.PutDataIntoRecyclerView(Home.java:74) at com.example.tokenauth.Home.access$000(Home.java:25) at com.example.tokenauth.Home$1.onResponse(Home.java:56) at retrofit2.ExecutorCallAdapterFactory$ExecutorCallbackCall$1$1.run(ExecutorCallAdapterFactory.java:68) at android.os.Handler.handleCallback(Handler.java:888) at android.os.Handler.dispatchMessage(Handler.java:100) at android.os.Looper.loop(Looper.java:213) at android.app.ActivityThread.main(ActivityThread.java:8178) at java.lang.reflect.Metho d.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:513) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1101) Please explain what is my mistake PS sorry for my English

JSON type

{
   "list":[
      {
         "Id":2,
         "Name":"temp",
         "Description":"Danger"
      },
      {
         "Id":1,
         "Name":"Water",
         "Description":"Danger"
      }
   ],
   "pageInfo":{
      "totalRows":2,
      "page":1,
      "pageSize":25,
      "isFirstPage":true,
      "isLastPage":true
   }
}

Interface.class

@GET("views/Notification")
Call<NotificationArray>getCarsJson();

ModelArray.class

public class NotificationArray {
    private CarsModel[] list;
    public CarsModel[] getList() {
        return list;
    }

    public void setMoviz(CarsModel[] list) {
        this.list = list;
    }
}

Home.class

public class Home extends AppCompatActivity {
RecyclerView recyclerView;

List<CarsModel> carsModels;
private CarsAdapter carsAdapter;
private RecyclerView cars_recyclerview;
NotificationArray notificationArray;

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

    cars_recyclerview=(RecyclerView)findViewById(R.id.cars_recyclerview);
    carsModels = new ArrayList<>();

    getCarsResponse();


}

public void getCarsResponse(){
    APIService service = ApiClient.getClient().create(APIService.class);
    Call<NotificationArray> call=service.getCarsJson();
    call.enqueue(new Callback<NotificationArray>() {
        @Override
        public void onResponse(Call<NotificationArray> call, Response<NotificationArray> response) {


            NotificationArray notificationArray= response.body();
            carsModels= new ArrayList<>(Arrays.asList(notificationArray.getList()));
            PutDataIntoRecyclerView(carsModels);


            Toast.makeText(Home.this,"Success",Toast.LENGTH_SHORT).show();
        }

        @Override
        public void onFailure(Call<NotificationArray> call, Throwable t) {
            Toast.makeText(Home.this,"Failed",Toast.LENGTH_SHORT).show();
            Log.e("failure",t.getLocalizedMessage());
        }

    });
}

private void PutDataIntoRecyclerView(List<CarsModel> carsModels) {
    CarsAdapter carsAdapter = new CarsAdapter( this, carsModels);
    cars_recyclerview.setLayoutManager(new LinearLayoutManager(this));
    recyclerView.setAdapter(carsAdapter);

}

Model.class

public class CarsModel {



    @SerializedName("Id")
    @Expose
    private String Id;
    @SerializedName("Name")
    @Expose
    private String Name;
    @SerializedName("Description")
    @Expose
    private String Description;

    public String getId() {
        return Id;
    }

    public void setId(String Id) {
        this.Id = Id;
    }

    public String getName() {
        return Name;
    }

    public void setName(String Name) {
        this.Name = Name;
    }

    public String getDescription() {
        return Description;
    }

    public void getDescription(String Description) {
        this.Description = Description;
    }


}

Adapter.class

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

    private List<CarsModel> carsModels;
    private Context context;


    public CarsAdapter(Context context, List<CarsModel> carsModels) {
        this.carsModels=carsModels;
        this.context=context;
    }

    @NonNull
    @Override
    public CarsAdapter.ViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
        View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.cars_list_item,viewGroup,false);
        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull CarsAdapter.ViewHolder viewHolder, int i) {
        viewHolder.car_name.setText(carsModels.get(i).getName());
        viewHolder.car_desc.setText(carsModels.get(i).getDescription());


    }

    @Override
    public int getItemCount() {
        return carsModels.size();
    }

    public class ViewHolder extends RecyclerView.ViewHolder {

        private TextView car_name,car_desc;
        public ViewHolder(@NonNull View itemView) {
            super(itemView);


            car_name=(TextView) itemView.findViewById(R.id.car_name);
            car_desc=(TextView)itemView.findViewById(R.id.car_desc);
        }
    }
}

I've been trying to get data on the RecycleView for a day now, but it doesn't work. An error comes out:

E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.tokenauth, PID: 8011 java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.recyclerview.widget.RecyclerView.setAdapter(androidx.recyclerview.widget.RecyclerView$Adapter)' on a null object reference at com.example.tokenauth.Home.PutDataIntoRecyclerView(Home.java:74) at com.example.tokenauth.Home.access$000(Home.java:25) at com.example.tokenauth.Home$1.onResponse(Home.java:56) at retrofit2.ExecutorCallAdapterFactory$ExecutorCallbackCall$1$1.run(ExecutorCallAdapterFactory.java:68) at android.os.Handler.handleCallback(Handler.java:888) at android.os.Handler.dispatchMessage(Handler.java:100) at android.os.Looper.loop(Looper.java:213) at android.app.ActivityThread.main(ActivityThread.java:8178) at java.lang.reflect.Metho d.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:513) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1101) Please explain what is my mistake PS sorry for my English

Answer 1

Inside Your Home Class:

private void PutDataIntoRecyclerView(List<CarsModel> carsModels) {
CarsAdapter carsAdapter = new CarsAdapter( this, carsModels);
cars_recyclerview.setLayoutManager(new LinearLayoutManager(this));
recyclerView.setAdapter(carsAdapter);
}

In The Last Code Line Change recyclerView.setAdapter(carsAdapter); to cars_recyclerview.setAdapter(carsAdapter);

Making it:

private void PutDataIntoRecyclerView(List<CarsModel> carsModels) {
CarsAdapter carsAdapter = new CarsAdapter( this, carsModels);
cars_recyclerview.setLayoutManager(new LinearLayoutManager(this));
cars_recyclerview.setAdapter(carsAdapter);
}

Answer 2

Change your recycler view object in PutDataIntoRecyclerView (last line of the function) from recyclerView -> cars_recyclerview

and also, You have created the object of adapter twice 1st at global scope and 2nd at PutDataIntoRecyclerView method. and you also need to remove the recyclerview object( RecyclerView recyclerView; ) created at global scope of you are not use it.