How to handle onBackPressed in Android Navigation Component

In this android programming source code example, we are going to handle onBackPressed in Android Navigation Component.

You can copy and adopt this source code example to your android project without reinventing the wheel.

Below is a step by step source code to handle onBackPressed in Android Navigation Component.

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=".BluetoothAndNavigation.BluetoothAndNavigationActivity14">

    <fragment
        android:id="@+id/nav_host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:defaultNavHost="true"
        app:navGraph="@navigation/nav_graph4"/>

</androidx.constraintlayout.widget.ConstraintLayout>

res/navigation/nav_graph4.xml

<?xml version="1.0" encoding="utf-8"?>
<navigation
    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:id="@+id/nav_graph4"
    app:startDestination="@id/navFragment14">

    <fragment
        android:id="@+id/navFragment14"
        android:name="com.bluapp.androidview2.BluetoothAndNavigation.NavFragment14"
        android:label="fragment_nav_fragment14"
        tools:layout="@layout/fragment_nav_fragment14" />


</navigation>

MainActivity.java

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;

import com.bluapp.androidview2.R;

public class BluetoothAndNavigationActivity14 extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_bluetooth_and_navigation14);
    }
}

fragment_nav_fragment14.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=".BluetoothAndNavigation.NavFragment14">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"
        android:text="Blank Fragment"/>

</androidx.constraintlayout.widget.ConstraintLayout>

NavFragment14.java

import androidx.activity.OnBackPressedCallback;
import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Toast;

public class NavFragment14 extends Fragment {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        OnBackPressedCallback callback = new OnBackPressedCallback(true) {
            @Override
            public void handleOnBackPressed() {
                Toast.makeText(getActivity(),"OnBackpress Click", Toast.LENGTH_LONG).show();
            }
        };
        requireActivity().getOnBackPressedDispatcher().addCallback(this, callback);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_nav_fragment14, container, false);

        return rootView;
    }
}

app/build.gradle

implementation 'androidx.navigation:navigation-fragment:2.1.0-alpha06'
implementation 'androidx.navigation:navigation-ui:2.1.0-alpha06'

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