Attempt to invoke virtual method 'android.view.Menu

Question

I don't have this code in MainActivity.java, I have it in one called Login.java

I have this error in the Logcat:

java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Menu
com.google.android.material.navigation.NavigationView.getMenu()' on a null object reference
    at com.store.Credenciales.Login.addMenuItemLogOut(Login.java:93)

My code in Login.java:93 is this function:

private void addMenuItemLogOut(){
    NavigationView navigationView= (NavigationView) findViewById(nav_view);
    Menu menu = navigationView.getMenu(); //Line 93
    menu.findItem(R.id.nav_signin).setVisible(false);
    menu.findItem(R.id.nav_send).setVisible(true);
}

And command to bring the function higher, when a user entered correct username and password

if(isLogin){
    addMenuItemLogOut(); //Here
    Intent intent = new Intent(getApplicationContext(), MainActivity.class);
    Bundle bundle =  new Bundle();
    bundle.putString("user_id", userd);
    intent.putExtras(bundle);
    startActivity(intent);
}

Answer 1

NullPointerException is thrown when an application attempts to use an object reference that has the null value.

You should use getHeaderView (int index) instead of getMenu() .

Gets the header view at the specified position.

Try with

 NavigationView navigationView       = findViewById(R.id.nav_view);
 navigationView.setNavigationItemSelectedListener(this);
 View header         = navigationView.getHeaderView(0);
 navigationView.getMenu().findItem(R.id.nav_signin).setVisible(false);
 navigationView.getMenu().findItem(R.id.nav_send).setVisible(true);