MSDN Magazine - January 2009 - (Page 32)

Figure 1 shows a sample ASP.NET HTTP handler that returns some XAML created on the fly. The ProcessRequest method sets the content type on the Response object and then writes out some XAML content, such as XAML composed dynamically, based on configuration data, parameters, or runtime conditions. By setting To associate the plug-in with an HTTP handler, or any other endpoint you choose, you use the usual Silverlight programming techniques. For example, you can use the Silverlight server control in an ASP.NET page: Silverlight 2 provides a rich and powerful API for downloading code on demand. the Expires property on the Response object, you can also prevent caching of the resource on the client. This may be helpful if the content you’re serving changes periodically and needs refreshing. Returning a dynamically generated XAP package is not much different from returning raw XAML text, except that a XAP package is not a plain text file. A XAP package is a ZIP file that contains an XML manifest and one or more assemblies. By using a package format, the team minimized the number of round-trips necessary to download the entire content required by a Silverlight application. Figure 2 shows an ASP.NET HTTP handler that writes the content of a XAP file out to the HTTP response stream. The sample code reads the XAP data from an existing file. It goes without saying that if you embed a ZIP library in your project, you could easily assemble the package on the fly by combining different DLLs and then creating a proper XML manifest file. If you’re returning XAP content, you set the content type of the response to application/octet-stream—the MIME type that commonly identifies generic binary content. Figure 2 An HTTP Handler that Returns a XAP Package using System; using System.Web; public class XapGenHandler : IHttpHandler { public void ProcessRequest (HttpContext context) { // XAP file to return string xapFile = " "; // Set the type of data we're returning context.Response.ContentType = "application/octet-stream"; // Create some XAML and return it down the wire content.Response.WriteFile(xapFile); In both examples, the factory for the Silverlight application lives on the Web server. This is an excellent approach if the host page needs to figure out dynamically which content to download. However, this is just one possible scenario. There’s another scenario that is probably more common—the need to download optional components for the current Silverlight application. In this case, the logic to select and download external content is all running on the client in the Silverlight plug-in. On-Demand Content Dynamically Generated XAP Silverlight 2 provides a rich and powerful API to download code and/or XAML on demand that you can use for downloading content and inserting it into the existing XAML document object model. All visual elements of a XAML tree feature a property called Children that you can use to programmatically add or remove child elements of any size. For example, you can append an entire user control downloaded from the same server or even from a trusted, opt-in remote server. The following line shows an example: StackPanel1.Children.Add(downloadedContent); The user control represented by the argument is added to the Children collection of a StackPanel XAML element. The rendering is immediate, and the user interface is updated in real time. You can do much more than just download content and attach it to the existing document object model. You can, for example, cache it locally in the local storage of the application and check your own cache for on-demand content before you go for a new request to the server. This approach gives you permanent storage of the downloaded content. However, in some cases this may be overkill. Another, simpler option exists that doesn’t require any extra work: letting the browser cache the XAP resource for you. Caching Downloaded Content } public bool IsReusable { get {return true;} } } The XAP package that you get from the Web server has no special meaning to the browser. The browser, therefore, will cache it as it caches anything else it gets from a Web server, adhering to the request cache policies determined by the cache-control and “expires” HTTP header in the request or similar meta tags in the host HTML page. Note that when you have a XAP resource to be downloaded in the browser, you can control caching via the settings in the page that you typically insert using meta tags or ASP.NET directive attributes. If the XAP resource is to be downloaded via an HTTP handler as in the previous example, then you can control caching for the specific request. Cutting Edge 32 msdn magazine

Table of Contents Feed for the Digital Edition of MSDN Magazine - January 2009

Toolbox CLR Inside Out Basic Instincts Cutting Edge Test Run First Look� Geneva Framework Silverlight Windows Mobile Service Station Security Briefs Extreme ASP.NET Foundations .NET Matters { End Bracket }

MSDN Magazine - January 2009

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