Why my arraylist size equal to 0 on the adapter page?

Question

I started to wrote app that gets input from the user (in edittext) and after pressing button it should pass the valued to another activity in custom listview. I found a problem during the debugging that the arraylist in the adapter getting null or 0. Here is the Adapter code and main activity. I hope someone could help me with this issue.

Adapter

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;

import androidx.recyclerview.widget.RecyclerView;

import java.util.ArrayList;
public class exampleAdapter extends RecyclerView.Adapter<exampleAdapter.ExampleViewHolder> {

    private ArrayList<exampleItem> mExampleList;

    public static class ExampleViewHolder extends RecyclerView.ViewHolder {
        public TextView mTextViewLine1;
        public TextView mTextViewLine2;
        public ImageView imageView;
        public ExampleViewHolder(View itemView) {
            super(itemView);
            mTextViewLine1 = itemView.findViewById(R.id.textview_line1);
            mTextViewLine2 = itemView.findViewById(R.id.textview_line2);
            imageView = itemView.findViewById(R.id.icond);
        }
    }
    public exampleAdapter(ArrayList<exampleItem> exampleList) {
        mExampleList = exampleList;
        this.notifyDataSetChanged();
    }
    @Override
    public ExampleViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.activity_example_item, parent, false);
        ExampleViewHolder evh = new ExampleViewHolder(v);
        return evh;
    }
    @Override
    public void onBindViewHolder(ExampleViewHolder holder, int position) {
        exampleItem currentItem = mExampleList.get(position);
        holder.mTextViewLine1.setText(currentItem.getLine1());
        holder.mTextViewLine2.setText(currentItem.getLine2());
        if (currentItem.getLineimg().equalsIgnoreCase("s")) {
            holder.imageView.setImageResource(R.drawable.salary);
        }
        if (currentItem.getLineimg().equalsIgnoreCase("e")){
            holder.imageView.setImageResource(R.drawable.money);
        }
    }
    @Override
    public int getItemCount() {
        return mExampleList.size();
    }
}

MainActivity2

import androidx.appcompat.app.AppCompatActivity;

import android.content.SharedPreferences;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;

import java.lang.reflect.Type;
import java.util.ArrayList;

public class MainActivity2 extends AppCompatActivity {

    private ArrayList<exampleItem> mExampleList = new ArrayList<>();

    private exampleAdapter mAdapter = new exampleAdapter(mExampleList);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);

        setInsertButton();
        loadData();

    }

    private void loadData() {
        SharedPreferences sharedPreferences = getSharedPreferences("shared preferences4", MODE_PRIVATE);
        Gson gson = new Gson();
        String json = sharedPreferences.getString("task list4", null);
        Type type = new TypeToken<ArrayList<exampleItem>>() {
        }.getType();
        mExampleList = gson.fromJson(json, type);
        if (mExampleList == null) {
            mExampleList = new ArrayList<>();
        }
    }

    private void saveData() {
        SharedPreferences sharedPreferences = getSharedPreferences("shared preferences4", MODE_PRIVATE);
        SharedPreferences.Editor editor = sharedPreferences.edit();
        Gson gson = new Gson();
        String json = gson.toJson(mExampleList);
        editor.putString("task list4", json);
        editor.apply();
    }

    private void setInsertButton() {
        Button buttonInsert = findViewById(R.id.insert);
        buttonInsert.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                final EditText line1 = findViewById(R.id.categ);
                final EditText lineimg = findViewById(R.id.summ);
                final EditText line2 = findViewById(R.id.date2);

                String lin1 = line1.getText().toString();
                String lin2 = line2.getText().toString();
                String lin3 = lineimg.getText().toString();


                insertItem(lin1, lin2, lin3);
                saveData();
                finish();

            }


            private void insertItem(String toString, String toString1, String toString2) {
                mExampleList.add(new exampleItem(toString, toString2, toString1));
                mAdapter.notifyItemInserted(mExampleList.size());
                mAdapter.notifyDataSetChanged();
            }
        });
    }
}

MainActivity

import android.content.Intent;
import android.os.Bundle;
import android.view.View;

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

import java.util.ArrayList;
public class MainActivity extends AppCompatActivity {
    ArrayList<exampleItem> mExampleList = new ArrayList<>();
    RecyclerView mRecyclerView;
    private exampleAdapter mAdapter = new exampleAdapter(mExampleList);
    private RecyclerView.LayoutManager mLayoutManager;

    @Override
    protected void onCreate(Bundle savedInstanceState1) {
        super.onCreate(savedInstanceState1);
        setContentView(R.layout.activity_main);

        findViewById(R.id.buttoni).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(MainActivity.this,MainActivity2.class);
                startActivity(intent);
            }
        });


        buildRecyclerView();
    }
    private void buildRecyclerView() {
        mRecyclerView = findViewById(R.id.recyclerview);
        mRecyclerView.setHasFixedSize(true);
        mLayoutManager = new LinearLayoutManager(this);
        mAdapter = new exampleAdapter(mExampleList);
        mRecyclerView.setLayoutManager(mLayoutManager);
        mRecyclerView.setAdapter(mAdapter);
    }
}

Answer 1

Bring out the inserItem method as separate from onClickListener and try out

private void insertItem(String toString, String toString1, String toString2) {
                mExampleList.add(new exampleItem(toString, toString2, toString1));
                mAdapter.notifyItemInserted(mExampleList.size());
                mAdapter.notifyDataSetChanged();
            }

you can remove this.notifydatachange() from adapter constructor

public exampleAdapter(ArrayList<exampleItem> exampleList) {
    mExampleList = exampleList;
    this.notifyDataSetChanged();
}