Turning cellphone to landscape- how to start at onStart()?

Question

Goal:
When I turn the cellphone from portrait to landscape I would like to begin from scratch that you start at onStart().

Problem:
What part am I missing in order to make it?

Thank you!

Info:
*I'm new in android
*I'm using API 23

---

MainActivity

package com.jfdimarzio.myapplication2;


import android.Manifest;
import android.app.Activity;
import android.content.Context;
import android.content.pm.PackageManager;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.location.LocationProvider;
import android.os.Bundle;
import android.support.v4.app.ActivityCompat;
import android.support.v7.app.AppCompatActivity;
import android.text.format.Time;
import android.util.Log;
import android.widget.TextView;

import java.text.DecimalFormat;


public class MainActivity extends AppCompatActivity
{
    private TextView texten = null;



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

        texten = new TextView(this);
        texten.setText("");
        setContentView(texten);
        Log.d("StateInfo", "onCreate");
        print("onCreate");
    }


    @Override
    protected void onStart()
    {
        super.onStart();
        Log.d("StateInfo", "onStart");
        print("onStart");
    }


    @Override
    protected void onResume()
    {
        super.onResume();
        Log.d("StateInfo", "onResume");
        print("onResume");
    }


    @Override
    protected void onPause()
    {
        super.onPause();
        Log.d("StateInfo", "onPause");
        print("onPause");
    }


    @Override
    protected void onStop()
    {
        super.onStop();
        Log.d("StateInfo", "onStop");
        print("onStop");
    }


    @Override
    protected void onDestroy()
    {
        super.onDestroy();
        Log.d("StateInfo", "onDestroy");
        print("onDestroy");
    }


    private void print(String text) {
        Time now = new Time();
        now.setToNow();
        String timeString = now.format("%H:%M:%S");
        String line = timeString + ": " + text + "\n";
        texten.setText(texten.getText() + line);
        texten.invalidate();
        texten.postInvalidate();
    }


}

---

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.jfdimarzio.myapplication2">

    <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"
        android:configChanges="orientation|screenSize|keyboardHidden">
        <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>

---

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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="com.jfdimarzio.myapplication2.MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</android.support.constraint.ConstraintLayout>

---

Answer 1

Delete this line from your AndroidManifest.xml:

android:configChanges="orientation|screenSize|keyboardHidden"

This line declares that you will handle these "configuration changes", rather than allowing the system to automatically destroy and recreate your activities. If you want the default handling, just get rid of this line.

Answer 2

If you want the Activity to start up and stay in landscape, you might as well set the activity to landscape mode:

<activity android:name=".MainActivity"
          android:screenOrientation="landscape">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

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