mainViewModel.getListLiveData().observe(MainActivity.this, new Observer<List<Student>>() {
            @Override
            public void onChanged(@Nullable List<Student> list) {
                if(list.size() > 0){
                    mainViewModel.getStudentLiveData().observe(MainActivity.this, new Observer<Student>() {
                        @Override
                        public void onChanged(@Nullable Student student) {

                        }
                    });
                }

            }
        });