Switching fragments

MainActivity.java

// Blablabla

/**
 * Loads and switches to a new fragment.
 * If a fragment with {@code tag} has already been loaded and was detached from the container,
 * this method will detach the current fragment and reattach the fragment back again, instead
 * of creating a new instance of the target fragment.
 *
 * @param cls {@code Class} of the new fragment
 * @param tag a tag to identify a fragment
 */
private void switchFragment(Class<? extends BaseFragment> cls, String tag) {
    Fragment oldFragment = fragmentManager.findFragmentById(R.id.container);

    // Check if the target fragment is already visible.
    if (oldFragment != null && oldFragment.getTag().equals(tag)) {
        return;
    }

    FragmentTransaction transaction = fragmentManager.beginTransaction();
    if (fragmentManager.findFragmentById(R.id.container) != null) {
        for (Fragment fragment : fragmentManager.getFragments()) {
            if (fragment != null) {
                transaction.detach(fragment);
            }
        }
    }
    if (fragmentManager.findFragmentByTag(tag) != null) {
        // The target fragment has been loaded before.
        transaction.attach(fragmentManager.findFragmentByTag(tag));
    } else {
        // Create a new instance of the fragment.
        Fragment fragment = Fragment.instantiate(this, cls.getName());
        // Set required fields and listeners for the fragment.
        // The listener interfaces are defined in the BaseFragment.
        /*
        ((BaseFragment) fragment).setContext(this);
        ((BaseFragment) fragment).setOnTitleChangedListener(this);
        ((BaseFragment) fragment).setOnAppBarLoadedListener(this);
        */
        transaction.attach(fragment).add(R.id.container, fragment, tag);
    }
    transaction.commit();
}

// Blablabla