Question

In Silverlight I want to be able to get the output from a Helper class like this:

    public MainPage()
    {
        InitializeComponent();

        String ouput;
        Helper helper = new Helper(url);

        Helper.invoke(output);

    }

I can’t see how to do that since in Helper Class I am obliged to do an asynchronous call:

    private String webserviceUrl;
    private XDocument xdoc = new XDocument();

    public Helper(String webserviceUrl)
    {
        this.webserviceUrl = webserviceUrl;
    }

    public void invoke(ref String output)
    {

        HttpWebRequest httpWebRequest = (HttpWebRequest)WebRequest.Create(this.webserviceUrl);
        try
        {
            HttpWebResponse httpWebResponse = (HttpWebResponse)httpWebRequest.BeginGetResponse(new AsyncCallback(HandlerWebResponse), httpWebResponse);

        }
        catch
        {

        }

  }

    private void HandlerWebResponse(IAsyncResult asynchronousResult)
    {
        HttpWebRequest request = (HttpWebRequest)asynchronousResult.AsyncState;
        HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(asynchronousResult);
        using (StreamReader streamReader1 = new StreamReader(response.GetResponseStream()))
        {
            string resultString = streamReader1.ReadToEnd();

        }
    }

Answer 1

Create an event to notify that the service has been successfully consumed. In the event parameters you can pass the result of the invoked web services.

public event Action<string> ResponseResult;

You can then invoke this event in your web response handler:

private void HandlerWebResponse(IAsyncResult asynchronousResult)
{
    HttpWebRequest request = (HttpWebRequest)asynchronousResult.AsyncState;
    HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(asynchronousResult);
    using (StreamReader streamReader1 = new StreamReader(response.GetResponseStream()))
    {
        string resultString = streamReader1.ReadToEnd();
        if (ResponseResult != null)
             ResponseResult(resultString);

    }
}

And in your code the initiates the service call you can subscribe to this event to get notified when it has finished:

Helper helper = new Helper(url);
public MainPage()
{
    InitializeComponent();

    Helper.ResponseResult += ResponseHandler;
    Helper.invoke(output);

}

public void ResponseHandler(string response)
{
    // do something with response
}