Android to Add an Up Button to the AppBar using java

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Full source code to implement an up/back button into our app, which navigates us back to our parent Activity. For this we have to make some small changes in our Manifest.xml file

Activity2.java

package com.example.application.upbuttonexample;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class Activity2 extends AppCompatActivity {
    private Button button2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_2);

        getSupportActionBar().setTitle("Activity 2");
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);

        button2 = (Button) findViewById(R.id.button2);
        button2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                openActivity3();
            }
        });
    }

    public void openActivity3() {
        Intent intent = new Intent(this, Activity3.class);
        startActivity(intent);
    }
}

Activity3.java

package com.example.application.upbuttonexample;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

public class Activity3 extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_3);

        getSupportActionBar().setTitle("Activity 3");
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    }
}

activity_2.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.application.upbuttonexample.Activity2">

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:text="open activity 3" />

</RelativeLayout>

activity_3.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.application.upbuttonexample.Activity3">

</RelativeLayout>

activity_main.xml

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

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:text="open activity 2" />

</RelativeLayout>

AndroidManifest.xml

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

    <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>
        <activity
            android:name=".Activity2"
            android:parentActivityName=".MainActivity"></activity>
        <activity
            android:name=".Activity3"
            android:parentActivityName=".Activity2"></activity>
    </application>

</manifest>

MainActivity.java

package com.example.application.upbuttonexample;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {
    private Button button;

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

        button = (Button) findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                openActivity2();
            }
        });
    }

    public void openActivity2() {
        Intent intent = new Intent(this, Activity2.class);
        startActivity(intent);
    }
}

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