public class Collapsebutton_Fragment extends Fragment {

Collapsebutton_Fragment cpb_fragment;
Animation_Fragment anim_fragment;
FragmentManager fragmentManager;

@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

    View rootView = inflater.inflate(R.layout.collapsebutton_fragment, container, false);

    //Look for an animation xml file with a good collapse animation
    final Animation collapse = AnimationUtils.loadAnimation(getActivity(),R.anim.collapse_animation);
    final Button button = (Button)rootView.findViewById(R.id.CollapseButton);
    cpb_fragment = new Collapsebutton_Fragment();
    anim_fragment = new Animation_Fragment();

    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            v.startAnimation(collapse);

            //wait for a certain time, then remove the button and start animation
            //remove is not functioning, why not?
            getFragmentManager().beginTransaction()
                    .remove(getFragmentManager().findFragmentById(R.id.CollapseButton))
                    .commit();

            //does not wait until the animation is finished
            getFragmentManager().beginTransaction()
                    .add(R.id.container_mainactivity,anim_fragment)
                    .addToBackStack(null)
                    .commit();
        }
    });

    return rootView;
}
}