How to Save an ArrayList of Custom Objects to SharedPreferences with Gson in Android

dependencies {
  implementation 'com.google.code.gson:gson:2.8.9'
}

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.application.gsonexample.MainActivity">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/recyclerview"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginBottom="100dp"
        android:background="@android:color/darker_gray" />

    <EditText
        android:id="@+id/edittext_line_1"
        android:layout_width="180dp"
        android:layout_height="wrap_content"
        android:layout_alignParentStart="true"
        android:layout_alignParentBottom="true"
        android:layout_marginBottom="52dp"
        android:hint="Line 1" />

    <EditText
        android:id="@+id/edittext_line_2"
        android:layout_width="180dp"
        android:layout_height="wrap_content"
        android:layout_alignParentStart="true"
        android:layout_alignParentBottom="true"
        android:hint="Line 2" />

    <Button
        android:id="@+id/button_insert"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignTop="@id/edittext_line_1"
        android:layout_marginStart="13dp"
        android:layout_marginTop="23dp"
        android:layout_toEndOf="@id/edittext_line_1"
        android:text="insert" />

    <Button
        android:id="@+id/button_save"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBaseline="@id/button_insert"
        android:layout_toEndOf="@+id/button_insert"
        android:text="save" />

</RelativeLayout>

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_margin="4dp"
    app:cardCornerRadius="4dp">

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_margin="4dp">

        <TextView
            android:id="@+id/textview_line1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Line 1"
            android:textColor="@android:color/black"
            android:textSize="20sp"
            android:textStyle="bold" />

        <TextView
            android:id="@+id/textview_line_2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_below="@+id/textview_line1"
            android:layout_marginStart="8dp"
            android:text="Line 2"
            android:textSize="15sp" />

    </RelativeLayout>

</android.support.v7.widget.CardView>

package com.example.application.gsonexample;

import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

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 ExampleViewHolder(View itemView) {
            super(itemView);
            mTextViewLine1 = itemView.findViewById(R.id.textview_line1);
            mTextViewLine2 = itemView.findViewById(R.id.textview_line_2);
        }
    }

    public ExampleAdapter(ArrayList<ExampleItem> exampleList) {
        mExampleList = exampleList;
    }

    @Override
    public ExampleViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.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());
    }

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

package com.example.application.gsonexample;

public class ExampleItem {
    private String mLine1;
    private String mLine2;

    public ExampleItem(String line1, String line2) {
        mLine1 = line1;
        mLine2 = line2;
    }

    public String getLine1() {
        return mLine1;
    }

    public String getLine2() {
        return mLine2;
    }
}

package com.example.application.gsonexample;

import android.content.SharedPreferences;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
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 MainActivity extends AppCompatActivity {
    ArrayList<ExampleItem> mExampleList;
    private RecyclerView mRecyclerView;
    private ExampleAdapter mAdapter;
    private RecyclerView.LayoutManager mLayoutManager;

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

        loadData();
        buildRecyclerView();
        setInsertButton();

        Button buttonSave = findViewById(R.id.button_save);
        buttonSave.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                saveData();
            }
        });
    }

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

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

        if (mExampleList == null) {
            mExampleList = new ArrayList<>();
        }
    }

    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);
    }

    private void setInsertButton() {
        Button buttonInsert = findViewById(R.id.button_insert);
        buttonInsert.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                EditText line1 = findViewById(R.id.edittext_line_1);
                EditText line2 = findViewById(R.id.edittext_line_2);
                insertItem(line1.getText().toString(), line2.getText().toString());
            }
        });
    }

    private void insertItem(String line1, String line2) {
        mExampleList.add(new ExampleItem(line1, line2));
        mAdapter.notifyItemInserted(mExampleList.size());
    }
}