main_graph.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/main_graph"
    app:startDestination="@id/blankFragment">

    <fragment
        android:id="@+id/blankFragment"
        android:name="com.example.navigationcomponent.BlankFragment"
        android:label="blank_fragment"
        tools:layout="@layout/blank_fragment" />
    <fragment
        android:id="@+id/threeFragment"
        android:name="com.example.navigationcomponent.ThreeFragment"
        android:label="three_fragment"
        tools:layout="@layout/three_fragment" />
    <fragment
        android:id="@+id/newFragment"
        android:name="com.example.navigationcomponent.NewFragment"
        android:label="new_fragment"
        tools:layout="@layout/new_fragment" />
</navigation>




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

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginEnd="116dp"
        android:text="actBtn1"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="actBtn2"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toStartOf="@+id/button"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />


    <androidx.fragment.app.FragmentContainerView
        android:id="@+id/nav_host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:defaultNavHost="true"
        app:navGraph="@navigation/main_graph" />



</androidx.constraintlayout.widget.ConstraintLayout>




MainActivity.java


public class MainActivity extends AppCompatActivity {

    NavController navController;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        navController = Navigation.findNavController(this, R.id.nav_host_fragment);

        Button button1 = findViewById(R.id.button);
        Button button2 = findViewById(R.id.button2);

    }

}