为什么下面的代码没有给我任何输出？

Question

以下代码既未显示任何错误，也未提供任何输出。实际上，它似乎并没有进入onResponse(String response)方法内部。我用来执行PHP代码的URL正常运行，当我在浏览器中加载它时，它会为我提供JSON输出。

我使用一种通用方法通过在println内放置onResponse(String response)来检查是否在上述函数中，但是它从未在控制台中提供任何输出。

public class FragmentE extends Fragment {

View view;
private static final String URL_PRODUCTS= "http://hostname.com/appapi.php";

//a list to store all the products
List<Product> productList;

//the recyclerview
RecyclerView recyclerView;

@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstance) {
    view = inflater.inflate(R.layout.fragment_e, container, false);
    recyclerView= (RecyclerView) view.findViewById(R.id.recylcerViewE);
//        recyclerView.setHasFixedSize(true);
    recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
    productList = new ArrayList<>();

    StringRequest stringRequest = new StringRequest(Request.Method.GET, URL_PRODUCTS, new Response.Listener<String>() {
    @Override
    public void onResponse(String response) {
        try {
            //converting the string to json array object
            JSONArray array = new JSONArray(response);

            //traversing through all the object
            for (int i = 0; i < array.length(); i++) {

                //getting product object from json array
                JSONObject product = array.getJSONObject(i);

                //adding the product to product list
                productList.add(new Product(
                        product.getInt("id"),
                        product.getString("title"),
//                                        product.getString("shortdesc"),
                        //  product.getDouble("rating"),
                        product.getDouble("price"),
                        product.getString("image")
                ));
            }

            //creating adapter object and setting it to recyclerview
            ProductsAdapter adapter = new ProductsAdapter(getActivity(), productList);
            recyclerView.setAdapter(adapter);
        } catch (JSONException e) {
            e.printStackTrace();
            }
        }
    },
    new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {

        }
    });

    //adding our stringrequest to queue
    Volley.newRequestQueue(getActivity()).add(stringRequest);
    return view;
}
}