FATAL EXCEPTION: main Process: com.example.todoapp, PID: 14053 java.lang.NullPointerException

Question

I am newbie to android. Please help me with this query,

Aim :

I have a RecyclerView in which there are many cards. I want to go to new activity when I click on card.

The Problem is: Why the null object reference is passed when someone clicks on card?

I found that the problem is in method called onClick inside ViewHolder class :

public void onClick(View v) {
            onCardviewButtonListener.performActionOnPosition(v,list.get(getAdapterPosition()));
        }

My error :

FATAL EXCEPTION: main Process: com.example.todoapp, PID: 14053 java.lang.NullPointerException: Attempt to invoke interface method 'void com.example.todoapp.CustomAdapterForInProgress$OnCardviewButtonListener.performActionOnPosition(android.view.View, com.example.todoapp.seeAllTaskCardDatatype)' on a null object reference at com.example.todoapp.CustomAdapterForInProgress$CustomViewHolder.onClick(CustomAdapterForInProgress.java:41) at android.view.View.performClick(View.java:6733) at android.view.View.performClickInternal(View.java:6691) at android.view.View.access$3400(View.java:802) at android.view.View$PerformClick.run(View.java:26499) at android.os.Handler.handleCallback(Handler.java:873) at android.os.Handler.dispatchMessage(Handler.java:99) at android.os.Looper.loop(Looper.java:226) at android.app.ActivityThread.main(ActivityThread.java:7178) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:503) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:942)

CustomAdapter.java file :

package com.example.todoapp;

import android.content.Context;
import android.content.Intent;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

import java.util.ArrayList;

public class CustomAdapterForInProgress extends RecyclerView.Adapter<CustomAdapterForInProgress.CustomViewHolder> {

    static  ArrayList<seeAllTaskCardDatatype> list;
    Context context;
    OnCardviewButtonListener onCardviewButtonListener;
    CustomAdapterForInProgress(ArrayList<seeAllTaskCardDatatype> passedList,Context passedContext,OnCardviewButtonListener onCardviewButtonListener){
        list = passedList;
        context = passedContext;
        this.onCardviewButtonListener = onCardviewButtonListener;
    }

    public interface OnCardviewButtonListener{
        void performActionOnPosition(View v,seeAllTaskCardDatatype obj);
    }

    public static class CustomViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {

        private TextView textView;
        private Button button;
        OnCardviewButtonListener onCardviewButtonListener;
        public CustomViewHolder(@NonNull View itemView) {
            super(itemView);
            textView = itemView.findViewById(R.id.taskInProgress);
            button = itemView.findViewById(R.id.moveToCompletedTask);
            itemView.setOnClickListener(this);
        }

        @Override
        public void onClick(View v) {
            onCardviewButtonListener.performActionOnPosition(v,list.get(getAdapterPosition()));
        }
    }



    @NonNull
    @Override
    public CustomViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.card_for_in_progress,parent,false);
        CustomViewHolder customViewHolder = new CustomViewHolder(view);
        return customViewHolder;

    }

    @Override
    public void onBindViewHolder(@NonNull CustomViewHolder holder, int position){
           seeAllTaskCardDatatype obj = list.get(position);
           holder.textView.setText(obj.getText());

    }



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

}

File implementing CustomAdapter :

package com.example.todoapp;

import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.content.Context;
import android.content.Intent;
import android.database.Cursor;
import android.os.Bundle;
import android.view.View;
import android.widget.Toast;

import java.util.ArrayList;

public class InProgress extends AppCompatActivity {
    DatabaseHelperForInProgress inDb;
    RecyclerView recyclerView;
    RecyclerView.Adapter adapter;
    CustomAdapterForInProgress.OnCardviewButtonListener onCardviewButtonListener;
    RecyclerView.LayoutManager layoutManager;
    ArrayList<seeAllTaskCardDatatype> inProgressList;
    Context context;
    Cursor cursor;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_in_progress);
        context = getApplicationContext();
        inDb = new DatabaseHelperForInProgress(this);

        cursor = inDb.getAllData();

        if(cursor.getCount() > 0  ){


            String[] id =  new String[cursor.getCount()];
            String[] tasks = new String[cursor.getCount()];
            int row =0;
            int column = 0;
            while(cursor.moveToNext()){

                for(int i=0;i<cursor.getColumnCount();i++){
                    if(i == 0){
                        id[row] = cursor.getString(i);
                    }
                    if(i == 1){
                        tasks[column] = cursor.getString(i);
                    }

                }
                row++;
                column++;
            }



            inProgressList = new ArrayList<>();
            for(int j=0;j<cursor.getCount();j++){
                inProgressList.add(new seeAllTaskCardDatatype(tasks[j],id[j]));
            }

            onCardviewButtonListener = new CustomAdapterForInProgress.OnCardviewButtonListener() {
                @Override
                public void performActionOnPosition(View v, seeAllTaskCardDatatype obj) {
                    Intent intent = new Intent(getApplicationContext(),CompletedTasks.class);
                    intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                    startActivity(intent);
                }
            };

            recyclerView = findViewById(R.id.inProgressRecycler);
            recyclerView.setHasFixedSize(true);
            layoutManager = new LinearLayoutManager(this);
            recyclerView.setLayoutManager(layoutManager);
            adapter = new CustomAdapterForInProgress(inProgressList,context,onCardviewButtonListener);
            recyclerView.setAdapter(adapter);
        }else{
            Toast.makeText(this,"No Task is in Progress",Toast.LENGTH_LONG).show();
        }






    }//onCreate Ends


}