Mark Monster

I was just looking around the web to find a Silverlight Control that’s has the features of a TagCloud. There are a lot of TagClouds in the world of Web 2.0, so probably almost everyone knows the way they work.

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This is already my fifth article on Silverlight Networking, with only the Credentials in mind. Please read my other articles first:

• Silverlight Networking - Getting credentials to work, unsuccessful.
• Silverlight Networking - Getting credentials to work, a possible work-around?
• Silverlight Networking - Getting credentials to work, a new WebRequest
• Silverlight Networking - Being Responsive to the WebRequest, a WebResponse 

I ended my last post with the trouble we get by using Javascript for the networking. Javascript doesn’t support calling outside the document’s domain. I’ve read through some hacking around this, but the hacks tend to work for a small time because they make use of bugs/holes inside the browsers that will be closed someday. But there’s a solution that will work for Javascript.

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There are quite some Mocking frameworks available. But sadly no one is ported to Silverlight, yet. I know about the porting of NUnit to Silverlight, but while working on Unit tests for the "Silverlight Networking through Javascript" library I found out there’s no Mocking framework yet to support the Silverlight runtime.

I would like to see some support for Silverlight from either Moq or Rhino Mocks. That’s because I like the way those Mocking frameworks work. I think they both make use of Castle’s DynamicProxy, so that’s another thing that first needs to become Silverlight enabled.

I’m sure more people thought about Mocking in a Silverlight runtime but didn’t find a solution too. I’m interested if anyone started to port one of the above Mocking frameworks to Silverlight. I’m not even totally sure if it’s possible but at least a part of Reflection.Emit exists.

What are anyone’s thoughts about Mocking in Silverlight?

This is already my fourth article on Silverlight Networking, with only the Credentials in mind. Please read my other articles first:

• Silverlight Networking - Getting credentials to work, unsuccessful.
• Silverlight Networking - Getting credentials to work, a possible work-around?
• Silverlight Networking - Getting credentials to work, a new WebRequest

In the last article I wrote about the WebRequest that gets translated from Silverlight to Javascript. In this article I will cover the converting of a Javascript WebResponse to a Silverlight WebResponse. Also the routing of the Response to the rightful listener is part of this article.

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This is already my third article on Silverlight Networking, with only the Credentials in mind. Please read my other articles first:

• Silverlight Networking - Getting credentials to work, unsuccessful.
• Silverlight Networking - Getting credentials to work, a possible work-around?

The workaround

It took me some time to get the work-around ready enough for this article. I must say we finally have the possibility to make a WebRequest with Credentials. Although we have another problem to solve, it’s crossdomain scripting! This article explains how you can make use of the Javascript abilities to make a WebRequest.

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A few days ago I blogged about the trouble of getting Credentials to work in Silverlight Networking. The troubles still exists sadly.  I’ve been thinking about creating a simple Silverlight application that makes use of the del.isio.us API. But sadly this API, as most of the online API’s do, makes use of Basic Auth over HTTP or HTTPS. I have thought about many different Silverlight applications that makes use of online API’s, but sadly I wasn’t able to create them because of the lacking of authentication possibilities. But I just got an idea, by thinking out-of-the-box. I might just get out of this very limiting box. Although it’s just an idea that’s not tried out in the wild.

The idea

Some time ago I watched a part of the "ASP.NET MVC Storefront" screencast which stated something about making use of the ASP.NET Ajax javascript libraries manually. This standalone library can be downloaded from here.

I know it is possible to call Javascript from within a Silverlight application, and also to call back to the Silverlight application from within Javascript. So why not making use of the Browser and Javascript capabilities for creating WebRequests. I’m not totally sure it’s possible to set the "Auth" header from Javascript, but I’ve got a good feeling about this. The only thing I still need is some time to work it out. More will follow…

One of the things the Silverlight Networking stack lacks is the support for credentials. Where we have things like the below in the full CLR, Silverlight doesn’t have any support.

httpWebRequest.Credentials = new NetworkCredential(username, password);

Investigation

So what about some investigation of the use of credentials. I remembered something about the usage of request headers for sending credentials. After a few minutes googleing I got support from a page on Oreilly about HTTP Headers. I found out the headername is "Authorization" and the value consist of authorization scheme and the credentials base64 encoded.

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I’ve been investigating Silverlight for a few days. This will be the first post in the Silverlight category, more will follow. After experimenting with some user interface effects I started investigating the Silverlight Networking possibilities. I was able to get some results of a network call but I wasn’t able to get it to the UI in the first place. So after some investigation I found out about the following solution.

Working Asynchronously

It’s only possible to work asynchronously with the networking stack. This is to prevent a hanging UI / Browser. This is not a very bad decision although it makes communicating with Webservices and other things on the web more difficult. I’m not into explaining a lot of things about networking and working asynchronously in common. When starting an asynchronous call to for example a Webservice you will give the call a pointer to the function that needs to be called on completion. This could be for example a not working callback function.

1 void helper_ResponseComplete(HttpResponseCompleteEventArgs e)
2 {
3   resultBox.Text = e.Response;
4 }

What’s wrong?

The trouble with the code example above is the call to a UI part ‘resultBox’. You could thing that the asynchronous call works on a background thread and that the callback automatically works on the UI thread. This is not the case. The trouble is that you don’t really get an exception that your doing something wrong, just nothing happens. It took me some time to find out the solution.

A simple solution

Every DependencyObject has a property called Dispatcher. This Dispatcher has some intelligent code to make it possible to get back to the UI thread. It is possible to call ‘BeginInvoke’ on the Dispatcher property. This method will require an Action delegate or a simple delegate with eventually arguments. I really like the use of a lambda expression. The following code wraps the code from the previous example in a lambda expression and uses the Dispatcher to get it back to the UI.

1 void helper_ResponseComplete(HttpResponseCompleteEventArgs e)
2 {
3   Dispatcher.BeginInvoke(() => resultBox.Text = e.Response);
4 }

Luckily the code being executed is just one line, so this simple solution works. But most of the time the code to be executed on the UI thread is more than just one line. So we need a more advanced solution.

A more advanced solution

The Dispatcher property also has a method to check whether or not the current thread is the UI thread. The example below checks if the current thread is an UI thread, when not it calls itself with the same arguments but then through the Dispatcher. The advantage with this is the possibility to have a code block of a few lines within the else-statement.

1 void helper_ResponseComplete(HttpResponseCompleteEventArgs e)
2 {
3   if(!Dispatcher.CheckAccess())
4     Dispatcher.BeginInvoke(()=>helper_ResponseComplete(e));
5   else
6   {
7     resultBox.Text = e.Response;
8   }
9 }

Updates 17/07

Some of my readers had additions for this article. So it’s fair to add this information at the end of the article I think.

Bart Czernicki noted: When calling a WCF service through a proxy, the results get properly dispatched on the UI thread.

Brian Leahy noted: When making use of databinding the binding will take of resynchronizing. His code example:

 1 void helper_ResponseComplete(HttpResponseCompleteEventArgs e)
 2 {
 3   this.Message= e.Response;
 4 }
 5 
 6 private String _message;
 7 public String Message
 8 {
 9   get
10   {
11     if(_message == null)
12     {
13       GetMessageAsync();
14     }
15     return _message;
16   }
17   set
18   {
19     _message = value;
20     PropertyChanged(value,”Message”);
21   }
22 }

Thanks for the comments!