SilverLight and Paging with Azure Data
[Cross-posted from here]
If you’ve been watching by blog at all lately, you know that I’ve been playing with some larger data sets and Azure storage, specifically Azure table storage. Last week I found myself working with a SilverLight application to visualize the resulting data and display it to the user, however I did not want to use the ADO.NET Data Services client (ATOM) due to the size of data in transmission. Consequently, I set up a web role that proxied the data calls and fed them back to the caller as JSON. Due to the limitation on Azure table storage of only returning 1,000 rows at a time, I needed to access the response headers in my SilverLight client to determine after each request if there were more rows waiting… and that was the rub… every time I tried to access the response headers collection (tried both with a WebClient and HttpWebRequest), I received a System.NotImplementedException.
I pounded my head on this for a few days with no success until a helpful twitterer (@silverfighter) provided me a link that got me rolling. The root of the problem was my ignorance of how SilverLight’s networking stack functioned. As I (now) understand it, by default any networking calls (WebClient or HttpWebRequest) are actually handled by the browser and not .NET. This results in you getting access to only what the browser object hands you, which in my case, did not include the response headers.
The key here is that SilverLight 3 provides you the ability to tell the browser that you’d rather handle those requests yourself. By simply registering the http protocol (you can actually do it as granular as a site level) as handled by the Silverlight client, “magic” happens and you suddenly have access to the properties of the WebClient (ResponseHeaders) and HttpWebRequest (Response.Headers) objects that you would have expected to. The magic line you need to add prior to issuing any calls is as follows:
bool httpResult = WebRequest.RegisterPrefix("http://", WebRequestCreator.ClientHttp);
(yes… that’s it…)
The links to the appropriate articles are as follows:
http://blogs.msdn.com/carlosfigueira/archive/2009/08/15/fault-support-in-silverlight-3.aspx
http://msdn.microsoft.com/en-us/library/dd470096(VS.95).aspx
http://blogs.msdn.com/silverlight_sdk/archive/2009/08/12/new-networking-stack-in-silverlight-3.aspx