invalid casting exception from datacontract json serializer

Question

I am working on a project for Windows Phone 7.1 in Visual Studio 2010. I am trying to download JSON data and deserialize it into a list of objects. The following is the code I am using to build the web request and handle the response.

public class HttpGetTask<T>
{
    public HttpGetTask(string url, Action<T> onPostExecute)
    {
        this.Url = url;
        this.OnPostExecute = onPostExecute;
    }

    public void Execute()
    {
        MessageBox.Show("We are in the task Execute method");
        if (this.OnPreExecute != null)
        {
            this.OnPreExecute();
        }

        // create the http request
        HttpWebRequest httpWebRequest = WebRequest.CreateHttp(this.Url);
        httpWebRequest.Method = "GET";
        httpWebRequest.Accept = "application/json";

        // get the response asynchronously
        httpWebRequest.BeginGetResponse(OnGetResponseCompleted, httpWebRequest);
    }

    private void OnGetResponseCompleted(IAsyncResult ar)
    {
        MessageBox.Show("We are in the OnGetResponseCompleted Method");
        var httpWebRequest = (HttpWebRequest)ar.AsyncState;

        // get the response
        HttpWebResponse response;
        try
        {
            response = (HttpWebResponse)httpWebRequest.EndGetResponse(ar);
        }
        catch (WebException e)
        {
            this.InvokeOnErrorHandler("Unable to connect to the web page.");
            return;
        }
        catch (Exception e)
        {
            this.InvokeOnErrorHandler(e.Message);
            return;
        }

        if (response.StatusCode != HttpStatusCode.OK)
        {
            this.InvokeOnErrorHandler((int)response.StatusCode + " " + response.StatusDescription);
            return;
        }

        // response stream
        var stream = response.GetResponseStream();

        // deserialize json
        var jsonSerializer = new DataContractJsonSerializer(typeof(T));
        var responseObject = (T)jsonSerializer.ReadObject(stream);

        // call the virtual method
        this.InvokeInUiThread(() => this.OnPostExecute(responseObject));
    }

The following are the DataContract classes I am using.

[DataContract]
public class OwnersList
{
    public List<Owner> Owners {get; set; }
}

[DataContract]
public class Owner
{
    [DataMember(Name = "oid")]
    public string Oid { get; set; }

    [DataMember(Name = "fname")]
    public string Fname { get; set; }

    [DataMember(Name = "lname")]
    public string Lname { get; set; }
}

The following is a sample of te JSON data I am trying to deserialize.

[{"oid":"1","fname":"John","lname":"Doe"},{"oid":"2","fname":"Mary","lname":"Smith"},{"oid":"3","fname":"Jimi","lname":"Hendrix"},{"oid":"4","fname":"Carole","lname":"King"},{"oid":"5","fname":"John","lname":"Winchester"},{"oid":"6","fname":"John","lname":"Hurt"},{"oid":"7","fname":"Rick","lname":"Grimes"},{"oid":"8","fname":"Haris","lname":"Okic"},{"oid":"9","fname":"Dino ","lname":"Okic"},{"oid":"10","fname":"Mirza","lname":"Cirkic"}]

When I run my app, I get an Invalid Casting Exception either when creating the serializer object, or on the jsonserializer.ReadObject(stream) line. Any ideas as to why this is happening?

Answer 1

Try to specify the property with a int:

[DataMember(Name = "oid")]
public string Oid { get; set; }

should be

[DataMember(Name = "oid")]
public int Oid { get; set; }