Asynchronous callback function is called multiple times (C#)

Question

This is a code snippet for processing HttpWebRequest by AsyncCallback function. Server side response well. It just responds only one return message, but this client code is called multiple times and give a terrible headache.

// Create Request HttpWebRequest request = (HttpWebRequest)WebRequest.Create(requestUri);

        try
        {
            // Make request with the following inline Asynchronous callback
            request.BeginGetResponse(new AsyncCallback((asynchronousResult) =>
                {
                    HttpWebRequest aRequest = (HttpWebRequest)asynchronousResult.AsyncState;
                    HttpWebResponse aResponse = (HttpWebResponse)aRequest.EndGetResponse(asynchronousResult);

                    using (StreamReader streamReader = new StreamReader(aResponse.GetResponseStream()))
                    {
                        // Deserialize the result
                        string jsonString = streamReader.ReadToEnd();
                        result = DeserializeToListOfObject(jsonString);

                        JavaScriptSerializer jS = new JavaScriptSerializer();
                        result = (List<object>)jS.Deserialize<List<object>>(jsonString);

                        if (result[0] is object[])
                        {
                            foreach (object message in (object[])result[0])
                            {
                                this.ReturnMessage = message;
                            }
                        }

I got the very continuous the same return messages. Anyone could help? Thanks in advance.

This probably has more to do with the code that follows this snippet. Don't call this code again until the response is received and you used "ReturnMessage". Consider starting a thread instead if that's a problem so you can just use GetResponse(). — Hans Passant
Thanks Hans. I solved this issue. It's not because of my asynchronous callback implementation. Just found a problem in another location. — Leonardo Redmond

Erhan A Erhan A · Accepted Answer · 2012-08-13T16:15:50

Seems the problem in the line

request.BeginGetResponse(new AsyncCallback((asynchronousResult) => {}

MSDN describes proper implementation of async request and response

notice the line :

IAsyncResult result=
        (IAsyncResult) myHttpWebRequest.BeginGetResponse(new AsyncCallback(RespCallback),myRequestState);

Hope this helps.

Asynchronous callback function is called multiple times (C#)

1 Answers