A task comes up to me in which I have to develop a private chat application for some product. I did some research on the XMPP protocol used by Facebook, Google etc. XMPP is a powerful protocol for public chat applications where thousands of users connect with each other. It has a separate XMPP server which listens to request and respond on it. There are also bunch of free XMPP servers available in the market.

Our goal is to provide a private chat where mid amount of users coordinate with particular resources time to time and the message format is not just simple like normal chat applications. We need to pass some advanced set of information to the recipient depending on which chat mode he has chosen. Then I chose WCF Duplex messaging where I can put all the business logic and intercept messages easily.

In order to make a chat application just like Facebook which have panel on the right and load chat popups that remains on the page I have to used Silverlight and ASP.Net and provide a special bridging between them. The reason of using Silverlight is that the ASP.Net doesn’t work with WCF Duplex Messaging because the framework of ASP.Net is request/response, whereas the Silverlight client is downloaded at client side and on each connection with WCF Service, service can send data back to client using default port 80.

I will not share how WCF Duplex messaging works, as I already published one article before on that but I will highlight the scenarios that can be implemented using very easy and simple code snippet provided to accomplish a bridging between ASP.Net and Silverlight.

Calling JavaScript function from Silverlight

string username = “Ovais”;

HtmlPage.Window.Invoke(“JSFunction”, username);

JSFunction is the javascript function implemented on the page where the Silverlight control is hosted. You can also pass the complete class object using Invoke method but that class object should be annotated by [ScriptableType()]attribute

[ScriptableType()]

public
class
ChatInfo

{

public
string UserName { get; set; }

public
int UserType {get; set; }

}

ChatInfo cInfo = new
ChatInfo() { UserName = “Ovais”, UserType = 1 };

HtmlPage.Window.Invoke(“JSFunction”, cInfo);

Getting Data in Silverlight from ASP.Net

In Silverlight you can read the HTML DOM using HTMLPage.Document object

HtmlPage.Document.GetElementById(“hiddenField1”).GetAttribute(“value”).ToString();

Using above two scenarios I succeeded passing data between both.

Happy coding!