I\'m starting with Android and in my project I\'m using this BottomBar. Love it, works pretty well. The code of my application is almost identical on to the one he uses in t
First you have a mistake in your Fragment transaction line, according with your layout should be:
transaction.replace(R.id.contentContainer, newFragment); // not R.id.bottomBar
Second, you should use supportFragmentManager instead of fragmentManager to work with support fragments, so implement the following way:
final FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
transaction.replace(R.id.contentContainer, newFragment);
transaction.addToBackStack(null);
transaction.commit();