Unable to display fetch data from MYSQL database in custom gridview in android

In my app I use grid view to display data. grid view is in a fragment.I already retrieve data from mysql database in Log cat but that json data not display in custom grid.

activity_product_list.xml

<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
xmlns:tools="http://schemas.android.com/tools"
tools:context=".DrawerActivity">


<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_marginBottom="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginLeft="8dp"
    android:layout_marginRight="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent">

    <TextView
        android:id="@+id/header2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="PRODUCTS : -"
        android:textSize="20sp"
        android:textStyle="bold"
        android:textColor="@color/blue"/>

    <GridView
        android:id="@+id/productlist"
        android:layout_below="@+id/header2"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        android:numColumns="2"
        android:horizontalSpacing="2dp"
        android:layout_marginTop="@dimen/activity_horizontal_margin">

    </GridView>

</RelativeLayout>

ProductListFragment.java

public class ProductListFragment extends Fragment {

List<Product> productList;
GridView gridView;
CustomProductList customProductList;
int categoryid;

@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.activity_product_list, container,false);

    gridView = (GridView) rootView.findViewById(R.id.productlist);
    final GlobalVariable ID = (GlobalVariable)getActivity().getApplication();
    categoryid = ID.getCategoryid();

    productList = new ArrayList<>();
    loadProduct();

    customProductList = new CustomProductList(getActivity(),productList);
    gridView.setAdapter(customProductList);

    return rootView;
}

@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
}

private void loadProduct() {
    String PRODUCT_URL = "http://192.168.0.101/cart/product/get_all_product.php?vcategoryid="+categoryid;
    StringRequest stringRequest= new StringRequest(Request.Method.GET, PRODUCT_URL, new Response.Listener<String>() {
        @Override
        public void onResponse(String response) {
            try {
                JSONObject obj = new JSONObject(response);
                JSONArray array = obj.getJSONArray("products");
                for (int i = 0; i < array.length(); i++){
                    //getting the user from the response
                    JSONObject userJson = array.getJSONObject(i);
                    Product product = new Product();
                    product.setProductid(userJson.getInt("productid"));
                    product.setProductName(userJson.getString("productname"));
                    product.setProductDesc(userJson.getString("productdesc"));
                    product.setPrice(userJson.getString("productprice"));

                    productList.add(product);
                    Log.e("product",userJson+"");
                }
                customProductList.notifyDataSetChanged();
                Log.e("product",customProductList+"");
                //customCategoryList = new CustomCategoryList(getActivity(),categoryList);
                //recyclerView.setAdapter(customCategoryList);
            } catch (JSONException e) {
                e.printStackTrace();
            }
        }
    }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {

        }
    });
    Volley.newRequestQueue(getActivity()).add(stringRequest);
}
}

custom_product_list.xml

<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">

<ImageView
    android:layout_width="200dp"
    android:layout_height="200dp"
    android:src="@drawable/home_appliances"/>

<TextView
    android:id="@+id/productName"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Redmi"
    android:textStyle="bold"
    android:textColor="@color/black"
    android:textSize="22sp"/>

<LinearLayout
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    android:layout_marginTop="5dp">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="RS."
        android:textSize="20sp"
        android:textStyle="bold"
        android:textColor="@color/black"/>

    <TextView
        android:id="@+id/price"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="9999"
        android:textSize="20sp"
        android:textStyle="bold"
        android:textColor="@color/blue"
        android:layout_marginLeft="10dp"/>
</LinearLayout>

CustomProductList.java

public class CustomProductList extends BaseAdapter {
private Context mCtx;
private List<Product> productList;

public CustomProductList(Context mCtx, List<Product> productList) {
    this.mCtx = mCtx;
    this.productList = productList;
}

@Override
public int getCount() {
    return 0;
}

@Override
public Object getItem(int i) {
    return null;
}

@Override
public long getItemId(int i) {
    return 0;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    LayoutInflater inflater = (LayoutInflater) mCtx
            .getSystemService(Context.LAYOUT_INFLATER_SERVICE);

    View gridView;

    if (convertView == null) {
        gridView = new View(mCtx);

        // get layout from mobile.xml
        gridView = inflater.inflate(R.layout.custom_product_list, null);

        TextView productname = (TextView) gridView.findViewById(R.id.productName);
        TextView price = (TextView) gridView.findViewById(R.id.price);

        // getting data for the row
        Product product = productList.get(position);
        // set data
        productname.setText(product.getProductName());
        price.setText(product.getPrice());
    } else {
        gridView = (View) convertView;
    }
    return gridView;
}
}

This is my code.All data comes from database in logcat as json..But All not display in grid.Please help me.Tell me What is the problem.