안드로이드- 회전시 데이터 유지하기

- 회전하면 reset되는 데이터 유지하는 방법 

<MainActivity.java>

package com.example.cycleex;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    public static final String PLAY_LEVEL = "playLevel";
    public static final String PLAY_SCORE = "playScore";
    TextView textLevel, textScore;
    Button btnLevelup, btnScoreup;
    int mLevel=0 , mScore=0;


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

        textLevel = findViewById(R.id.textLevel);
        textScore = findViewById(R.id.textScore);
        btnLevelup = findViewById(R.id.btnLevelup);
        btnLevelup.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                mLevel++;
                textLevel.setText("레벨: "+mLevel );
            }
        });

        btnScoreup = findViewById(R.id.btnScoreup);
        btnScoreup.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                mScore +=100;
                textScore.setText("점수 : " +mScore);
            }
        });

        if(savedInstanceState == null){

        }
        else{
            mLevel = savedInstanceState.getInt(PLAY_LEVEL);
            mScore = savedInstanceState.getInt(PLAY_SCORE);
            textLevel.setText("레벨: "+ mLevel);
            textScore.setText("점수: "+ mScore);
        }

    }

    @Override
    protected void onSaveInstanceState(@NonNull Bundle outState) {
        outState.putInt(PLAY_LEVEL, mLevel);
        outState.putInt(PLAY_SCORE, mScore);
        super.onSaveInstanceState(outState);
    }
}

<activity_main.xml>

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
    android:orientation="vertical"
    tools:context=".MainActivity" >

    <TextView
        android:id="@+id/textLevel"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="15dp"
        android:text="레벨 : 0" />

    <Button
        android:id="@+id/btnLevelup"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="레벨업" />

    <TextView
        android:id="@+id/textScore"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="15dp"
        android:text="점수 : 0" />

    <Button
        android:id="@+id/btnScoreup"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="점수증가" />
</LinearLayout>