如何检查评级栏是否已在Android中被评级？

ratingBar ratingbar = (ratingBar)findViewById(R.id.ratingBar);
@Override
    public void onClick(View view) {
        switch (view.getId()){
            case R.id.ratingBar:
                 if(ratingbar.getrating() == 0.0){

                    //set what you want
                     }else{

                    //give error if ratingbar not changed
                     }
            break;
    }
}