How to resolve Android Volley gson requests to object lists/collections
I’m trying to make a gson request using android volley. At the moment it is working fine and I am happy. But why do I try to get a List<> or object collection, my code no longer works.
Current code:
public class ReviewModel
{
public long Id;
public Strring Description;
}
Here’s how I use my gson class:
GsonRequest<ReviewModel> jsObjRequest = new GsonRequest<ReviewModel>(Request.Method.GET,
url, ReviewModel.class, new Response.Listener<ReviewModel>() {
@Override
public void onResponse(ReviewModel response) {
ReviewsHandleOkResponse(response);
}
}, new ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
ReviewsHandleErrorResponse(error);
}
});
Network.getInstance(getActivity()).addToRequestQueue(jsObjRequest);
}
Here is my Volley GSON request class:
public class GsonRequest<T> extends Request<T> {
private final Gson gson = new Gson();
private final Class<T> clazz;
private final Map<String, String> headers;
private final Map<String, String> params;
private final Listener<T> listener;
/**
* Make a GET request and return a parsed object from JSON.
*
* @param url
* URL of the request to make
* @param clazz
* Relevant class object, for Gson's reflection
* @param headers
* Map of request headers
*/
public GsonRequest(int method, String url, Class<T> clazz,
Map<String, String> headers, Map<String, String> params,
Listener<T> listener, ErrorListener errorListener) {
super(method, Network.getFullUrl(url), errorListener);
this.clazz = clazz;
this.headers = headers;
this.params = params;
this.listener = listener;
}
/**
* Recieves header
*
* @param method
* @param url
* @param clazz
* @param params
* @param listener
* @param errorListener
*/
public GsonRequest(int method, String url, Class<T> clazz,
Map<String, String> params, Listener<T> listener,
ErrorListener errorListener) {
super(method, Network.getFullUrl(url), errorListener);
this.clazz = clazz;
this.headers = new HashMap<String, String>();
this.params = params;
this.listener = listener;
}
/**
* No params or headers
*
* @param method
* @param url
* @param clazz
* @param listener
* @param errorListener
*/
public GsonRequest(int method, String url, Class<T> clazz,
Listener<T> listener, ErrorListener errorListener) {
super(method, Network.getFullUrl(url), errorListener);
this.clazz = clazz;
this.headers = new HashMap<String, String>();
this.params = new HashMap<String, String>();
this.listener = listener;
}
@Override
public Map<String, String> getHeaders() throws AuthFailureError {
return headers != null ? headers : super.getHeaders();
}
@Override
public Map<String, String> getParams() throws AuthFailureError {
return params != null ? params : super.getParams();
}
@Override
protected void deliverResponse(T response) {
listener.onResponse(response);
}
@Override
protected Response<T> parseNetworkResponse(NetworkResponse response) {
try {
String json = new String(response.data,
HttpHeaderParser.parseCharset(response.headers));
return Response.success(gson.fromJson(json, clazz),
HttpHeaderParser.parseCacheHeaders(response));
} catch (UnsupportedEncodingException e) {
return Response.error(new ParseError(e));
} catch (JsonSyntaxException e) {
return Response.error(new ParseError(e));
}
}
}
However, when I parse it to List<ReviewModel>
I get a compilation error.
Based on my research, I need to do something:
Type collectionType = new TypeToken<ArrayList<ReviewModel>>(){}.getType();
api/v1/reviews/products/{productId}/{pageNumber}/{pageSize}
String url = "api/v1/reviews/products/" + productId + "/" + currentPage + "/" + pageSize;
GsonRequest<ArrayList<ReviewModel>> jsObjRequest = new GsonRequest<ArrayList<ReviewModel>>(Request.Method.GET,
url, (Class<ArrayList<ReviewModel>>) collectionType, new Response.Listener<ArrayList<ReviewModel>>() {
@Override
public void onResponse(ArrayList<ReviewModel> response) {
ReviewsHandleOkResponse(response);
}
}, new ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
ReviewsHandleErrorResponse(error);
}
});
Network.getInstance(getActivity()).addToRequestQueue(jsObjRequest);
}
But this gives me the following error:
10-28 21:12:59.940: E/AndroidRuntime(28564):
java.lang.RuntimeException: Unable to start activity
ComponentInfo{com.menu/com.menu.activities.ProductViewActivity}:
java.lang.ClassCastException:
com.google.gson.internal.$Gson$Types$ParameterizedTypeImpl cannot be
cast to java.lang.Class
Do I need to modify my GsonRequest class and add another constructor that doesn’t take the type class?
Solution
Use YourClass[]
as the list of objects in the Volley request. It solved my problem. The following code should help you:
GsonRequest<ReviewModel[]> jsObjRequest = new GsonRequest<ReviewModel[]>(Request.Method.GET,
url, ReviewModel[].class, new Response.Listener<ReviewModel[]>() {
@Override
public void onResponse(ReviewModel[] response) {
ReviewsHandleOkResponse(response);
}
}, new ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
ReviewsHandleErrorResponse(error);
}
});
Network.getInstance(getActivity()).addToRequestQueue(jsObjRequest);
}