Android片段上的多个按钮

Question

在片段中，单击按钮时，它们将打开不同的片段。单击signup_b时，将打开新的片段，但是单击signin_b时，将不打开新的片段。

 public void onViewCreated(final View view, @Nullable Bundle savedInstanceState) {

    signin_b = view.findViewById(R.id.sign_in_button);
    signup_b = view.findViewById(R.id.sign_up_button);
    //signin_b.setOnClickListener(this);
    //signup_b.setOnClickListener(this);
    signup_b.setOnClickListener(new View.OnClickListener() {

        public void onClick (View v){

            question = new RegisterQuestionFragment();
            getFragmentManager().beginTransaction().replace(R.id.main_fragment,question,"information").addToBackStack(null).commit();
        }
    });
    signin_b.setOnClickListener(new View.OnClickListener() {

        public void onClick (View v){

            log = new LoginFragment();
            getFragmentManager().beginTransaction().replace(R.id.main_fragment,log,"log").addToBackStack(null).commit();
        }
    });
}