Question

I am able to consume a service asynchronously like below:

public void PostMethodResponse()
{
    try
    {
        HttpWebRequest myRequest = (HttpWebRequest)WebRequest.Create(_url);
        myRequest.Method = "POST";
        myRequest.Headers["SOAPAction"] = _action;
        myRequest.ContentType = "text/xml; charset=utf-8";
        myRequest.Accept = "text/xml";
        myRequest.BeginGetRequestStream(new AsyncCallback(GetRequestStreamCallback), myRequest);
    }
    catch (Exception ex)
    {
        throw ex;
    }
}

private void GetRequestStreamCallback(IAsyncResult asynchronousResult)
{
    try
    {
        HttpWebRequest request = (HttpWebRequest)asynchronousResult.AsyncState;

        System.IO.Stream postStream = request.EndGetRequestStream(asynchronousResult);
        byte[] byteArray = System.Text.Encoding.UTF8.GetBytes(_postData);                
        postStream.Write(byteArray, 0, byteArray.Length);
        postStream.Close();
        // Start the asynchronous operation to get the response
        request.BeginGetResponse(new AsyncCallback(GetResponseCallback), request);
    }
    catch (Exception ex)
    {
        throw ex;
    }
}

private void GetResponseCallback(IAsyncResult asynchronousResult)
{
    try
    {
        HttpWebRequest request = (HttpWebRequest)asynchronousResult.AsyncState;
        HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(asynchronousResult);
        Stream streamResponse = response.GetResponseStream();
        StreamReader streamRead = new StreamReader(streamResponse);
        string responseString = streamRead.ReadToEnd();
        // Close the stream object
        streamResponse.Close();
        streamRead.Close();
        // Release the HttpWebResponse
        response.Close();
        _response = responseString;                    

    }
    catch (Exception ex)
    {
        _response = ex.Message;

    }
}

I am calling the PostMethodResponse() function (which is in Model Class) from a ViewModel class. I am able get the response in GetResponseCallback function but how can i return that Response to ViewModel and then to View(Front End .xaml). To get the Response, We can fire an event GetResponseCallback function and then catch it ViewModel Class and Fire the same event ViewModel and Catch it View, But this is a not a right way.

Please help me in understanding the MVVM architecture call web services.

Thanks in advance.

Answer 1

1. Add the callback to your viewmodel to the BeginGetRequestStream object state parameter.
2. Get the callback out of the asynchronousResult in GetResponseCallback. Cast it to your call back type and call it back with your response.

Like this:

    class HttpRequest<T>
{
    internal HttpRequest(HttpWebRequest webRequest, Action<T> callback)
    {
        WebRequest = webRequest;
        Callback = callback;
    }

    internal HttpWebRequest WebRequest { get; private set; }
    internal Action<T> Callback { get; private set; }
}
class Class1
{
    private Uri _url;
    private string _action;
    private string _postData;

    public void PostMethodResponse(Action<string> callback)
    {
        try
        {
            HttpWebRequest myRequest = (HttpWebRequest)WebRequest.Create(_url);
            myRequest.Method = "POST";
            myRequest.Headers["SOAPAction"] = _action;
            myRequest.ContentType = "text/xml; charset=utf-8";
            myRequest.Accept = "text/xml";
            myRequest.BeginGetRequestStream(GetRequestStreamCallback, new HttpRequest<string>(myRequest, callback));
        }
        catch (Exception ex)
        {
            // log blah
        }
    }

    private void GetRequestStreamCallback(IAsyncResult asynchronousResult)
    {
        try
        {
            HttpRequest<string> request = (HttpRequest<string>)asynchronousResult.AsyncState;

            System.IO.Stream postStream = request.WebRequest.EndGetRequestStream(asynchronousResult);
            byte[] byteArray = System.Text.Encoding.UTF8.GetBytes(_postData);
            postStream.Write(byteArray, 0, byteArray.Length);
            postStream.Close();
            // Start the asynchronous operation to get the response
            request.WebRequest.BeginGetResponse(GetResponseCallback, request);
        }
        catch (Exception ex)
        {
            // nothing to see, move along
        }
    }

    private void GetResponseCallback(IAsyncResult asynchronousResult)
    {
        try
        {
            HttpRequest<string> request = (HttpRequest<string>)asynchronousResult.AsyncState;
            HttpWebResponse response = (HttpWebResponse)request.WebRequest.EndGetResponse(asynchronousResult);
            Stream streamResponse = response.GetResponseStream();
            if (streamResponse != null)
            {
                StreamReader streamRead = new StreamReader(streamResponse);
                string responseString = streamRead.ReadToEnd();
                // Close the stream object
                streamResponse.Close();
                streamRead.Close();
                // Release the HttpWebResponse
                response.Close();
                request.Callback(responseString);
            }
        }
        catch (Exception )
        {

        }
    }
}