Fragment addToBackStack() and popBackStackImmediate() not working

Question

I am currently building an application for Android (14 <= SDK <= 21) by using one ActionBarActivity and more Fragments, such as ListFra

Answer 1

I had to call beginTransaction() and commit() of FragmentManager manually.
Solved by overriding onBackPressed():

@Override
public void onBackPressed() {
    ...
    if (fragmentManager.getBackStackEntryCount() > 1){
        fragmentManager.popBackStackImmediate();
        fragmentManager.beginTransaction().commit();
    } else {
        //handle finish
        finish(); // Closes app
    }
}