Add Activities to Bottom Nav Bar - Attempt to invoke virtual method 'void com.google.android.material.bottomnavigation

Question

Am trying to add activities to android-x material design Bottom Navigation Bar but it's not work.

Am using 1 activity as abstract which extends AppCompactActivity which implements BottomNavigationView.OnNavigationItemSelectedListener and abstract methods getContentViewId() for layout xml file and getNavigationItemId to get menu item selected but am still getting a null pointer

Base Activity

public abstract class Main2Activity extends AppCompatActivity implements
        BottomNavigationView.OnNavigationItemSelectedListener {

    protected BottomNavigationView navigationView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(getContentViewId());

        BottomNavigationView navigationView = (BottomNavigationView) findViewById(R.id.navigation);
        navigationView.setOnNavigationItemSelectedListener(this);

    }

    @Override
    protected void onStart() {
        super.onStart();
        updateNavigationBarState();
    }

    @Override
    public void onPause() {
        super.onPause();
        overridePendingTransition(0, 0);
    }

    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        if (item.getItemId() != getNavigationMenuItemId()){
            switch (item.getItemId()){
                case R.id.navigation_home:
                    Intent homeIntent = new Intent(this, HomeActivity.class);
                    startActivity(homeIntent);
                    break;
                case R.id.navigation_vets:
                    Intent vetIntent = new Intent(this, VetActivity.class);
                    startActivity(vetIntent);
                    break;
                case R.id.navigation_agrovets:
                    Intent agrovetIntent = new Intent(this, AgrovetActivity.class);
                    startActivity(agrovetIntent);
                    break;
            }
            finish();
        }
        return true;
    }


    private void updateNavigationBarState() {
        int actionId = getNavigationMenuItemId();
        selectBottomNavigationBarItem(actionId);
    }

    private void selectBottomNavigationBarItem(int itemId) {
        Menu menu = navigationView.getMenu();
        for (int i =0, size = menu.size(); i< size; i++){
            MenuItem item = menu.getItem(i);
            boolean shouldBeChecked = item.getItemId() == itemId;
            if (shouldBeChecked){
                item.setChecked(true);
                break;
            }
        }
    }

    abstract int getContentViewId();
    abstract int getNavigationMenuItemId();
}

Sample of Bottom Navigation activities

public class HomeActivity extends Main2Activity {
    private PreferenceUtil preferenceUtil;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    int getContentViewId() {
        return R.layout.activity_home;
    }

    @Override
    int getNavigationMenuItemId() {
        return R.id.navigation_home;
    }
}

xml file for BottomNavigation

<?xml version="1.0" encoding="utf-8"?>
<com.google.android.material.bottomnavigation.BottomNavigationView
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/navigation"
    android:layout_width="match_parent"
    android:layout_height="56dp"
    android:layout_gravity="start"
    app:menu="@menu/navigation" />

Menu xml file

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

    <item
        android:id="@+id/navigation_home"
        android:icon="@drawable/ic_home_black_24dp"
        android:title="@string/title_home" />

    <item
        android:id="@+id/navigation_vets"
        android:icon="@drawable/"
        android:title="@string/title_dashboard" />

    <item
        android:id="@+id/navigation_agrovet"
        android:icon="@drawable/drug"
        android:title="@string/title_notifications" />

    <item
        android:id="@+id/navigation_account"
        android:icon="@drawable/baseline_account_box_24"
        android:title="@string/title_account" />

</menu>

After Login it should move to Home Activity with Bottom Navigation Here's the error

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.lukmo.kamsos, PID: 25461
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.lukmo.kamsos/com.lukmo.kamsos.UserInterface.HomeActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.android.material.bottomnavigation.BottomNavigationView.setOnNavigationItemSelectedListener(com.google.android.material.bottomnavigation.BottomNavigationView$OnNavigationItemSelectedListener)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2928)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3063)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1823)
        at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:198)
        at android.app.ActivityThread.main(ActivityThread.java:6729)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.android.material.bottomnavigation.BottomNavigationView.setOnNavigationItemSelectedListener(com.google.android.material.bottomnavigation.BottomNavigationView$OnNavigationItemSelectedListener)' on a null object reference
        at com.lukmo.kamsos.UserInterface.Main2Activity.onCreate(Main2Activity.java:37)
        at com.lukmo.kamsos.UserInterface.HomeActivity.onCreate(HomeActivity.java:12)
        at android.app.Activity.performCreate(Activity.java:7136)
        at android.app.Activity.performCreate(Activity.java:7127)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1272)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2908)

Answer 1

I answered it by include Bottom Navigation layout file to every layout xml file

    <include
        android:id="@+id/navigation"
        layout="@layout/element_bottom_navigation"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true" />