Survive Configuration change with ViewModel

Manifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="hego.android.savestatewithviewmodel">

    <uses-permission android:name="android.permission.INTERNET"/>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

========================================================================

Mainactivity.java

package hego.android.savestatewithviewmodel;

import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.LiveData;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProvider;
import androidx.lifecycle.ViewModelProviders;

import android.content.Context;
import android.os.Bundle;
import android.view.View;
import android.webkit.WebResourceRequest;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    private TextView tv;
    private Button button;
    private MainActivityViewModel mainActivityViewModel;

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

        tv = (TextView)findViewById(R.id.tv);

        mainActivityViewModel = ViewModelProviders.of(this).get(MainActivityViewModel.class);
        LiveData<String> liveData = mainActivityViewModel.getNumber();

        liveData.observe(this, new Observer<String>() {
            @Override
            public void onChanged(String s) {
                tv.setText(s);
            }
        });


        button = (Button)findViewById(R.id.button);
        button.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        if (v.getId()==R.id.button){
            mainActivityViewModel.createNumber();
        }
    }
}
=========================================================================
MainActivityViewModel.java (simple java file)

package hego.android.savestatewithviewmodel;

import android.content.Context;
import android.util.Log;
import android.webkit.WebView;

import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.ViewModel;

import java.util.Random;


public class MainActivityViewModel extends ViewModel {
    private String TAG = this.getClass().getSimpleName();
    private MutableLiveData<String> myRandomNumber;

    public MutableLiveData<String> getNumber() {
        Log.i(TAG, "Get number");
        if (myRandomNumber == null) {
            myRandomNumber = new MutableLiveData<>();
            createNumber();
        }
        return myRandomNumber;
    }

    public void createNumber() {
        Log.i(TAG, "Create new number");
        Random random = new Random();
        myRandomNumber.setValue("Number: " + (random.nextInt(10 - 1) + 1));
    }

    @Override
    protected void onCleared() {
        super.onCleared();
        Log.i(TAG, "ViewModel Destroyed");
    }
}
==========================================================================
activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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=".MainActivity">

    <TextView
        android:id="@+id/tv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintHorizontal_bias="0.498"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.053" />

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="28dp"
        android:text="Button"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.498"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/tv" />


</androidx.constraintlayout.widget.ConstraintLayout>
==================================================================
build.gradle (app level)

apply plugin: 'com.android.application'

android {
    compileSdkVersion 29
    buildToolsVersion "29.0.3"

    defaultConfig {
        applicationId "hego.android.savestatewithviewmodel"
        minSdkVersion 23
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(dir: "libs", include: ["*.jar"])
    implementation 'androidx.appcompat:appcompat:1.2.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.0.1'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test.ext:junit:1.1.2'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'

    def lifecycle_version = "1.1.1"
    implementation "android.arch.lifecycle:extensions:$lifecycle_version"
    annotationProcessor "android.arch.lifecycle:compiler:$lifecycle_version"

}