MSDN Magazine - July 2008 - (Page 54)

date a DOM subtree, you should remove unwanted wrapper service. From a design perspective, several elements and add new ones. While this approach is classes in Figure 6 are treated as services—stock quote neat and clean from a design perspective, it can have provider, data finder, output renderer and, as you’ll performance problems. see later in this column, also an input adapter. Nearly all browsers also support the innerHTML property on their DOM elements. It sets or retrieves Implementing the HTM Pattern the HTML between the start and end tags of the givFigure 7 shows the contract of the stock quote en element. The property was introduced with the service I’m using in the sample implementation of DHTML object model of Internet Explorer® 4.0 but the HTM pattern. The service is built around offline never made its way to the official DOM API. Comand online data providers. The offline data provider pared to the DOM API, though, innerHTML is much returns stale values for quotes and changes, whereas faster, especially when it comes to creating complex the online provider connects to a real finance service structures of elements. A good place to read about and returns live data. performance of innerHTML versus DOM is at go.micro Both providers rely on an internal finder composoft.com/fwlink/?LinkId=116828. The innerHTML is not free Figure 5 Service that nent to actually get data. The finder component is of issues. Read about possible problems to be aware Supports HTML Message characterized by an interface and the actual finder of at go.microsoft.com/fwlink/?LinkId=116827. class is read from the configuration file. The default finder component for the offline provider uses the Microsoft .NET HTML Message Pattern Framework Random class to generate just random numbers. A The goal of HTM pattern is having the server generate blocks finder component for the online provider may use any public Web of HTML markup to be displayed in the browser. A possible im- services that return financial information. plementation consists of making a call to a remote URL (either Any data that is obtained through a finder class is then composed a service or an HTTP handler) and receiving an HTML snippet into an HTML snippet using a renderer class. The renderer comready for display. ponent exposes an interface and can be replaced by simply changThe implementation of HTM relies entirely on the code you have ing a setting in the configuration file. The default HTML renderer on the server—specifically, the AJAX service layer. This is yet an- builds a table with some hardcoded styles. In this month’s source other good reason to favor the creation of an AJAX-specific mid- code, you’ll find out that the actual HTML renderer is a class dedle layer that isolates your core services rived from the default renderer that also from AJAX and presentation needs and adds a last update label. The code snippet concerns (see Figure 1). below shows the interfaces of the finder To support the HTML Message patand rendered classes: tern, an AJAX application needs services namespace Samples.Services.FinanceInfo { that accomplish the task for which they public interface IFinanceInfoFinder have been created and can translate their { string ProviderName { get; } calculated results to HTML snippets. StockInfo[] FindQuoteInfo Figure 5 illustrates this. (string symbols); } The service composability principle public interface IFinanceInfoRenderer is evident here. It’s just a variation of the { string GenerateHtml principle of reusability. In general, it ap(StockInfo[] stocks); plies to service-oriented architectures } } (SOAs) where you orchestrate business processes through composition languages The interfaces guarantee smooth inlike Web Services Business Process Exteroperability as the data obtained by ecution Language (WS-BPEL) and get a the finder flows directly into the methparent service process resulting from the ods of the renderer. concatenation of a few others. In this implementation, the GenerateAn AJAX service that outputs HTML Html method of the renderer builds may be seen as the composition of a core a table based on some predefined setservice that gets its data and a renderer tings. In general, it can use any other service that massages it into HTML. Figstyle information that may be passed ure 6 shows the composed architecture of around from the client. However, the a service that returns stock quotes. stock quote service is designed to pick In this implementation, I’m just com- Figure 6 Stock Quote Service that Supports up any renderer “service” that is configposing classes to obtain a parent and HTML Message ured on the server as the official HTML 54 msdn magazine Cutting Edge http://go.microsoft.com/fwlink/?LinkId=116828 http://go.microsoft.com/fwlink/?LinkId=116828 http://go.microsoft.com/fwlink/?LinkId=116827

Table of Contents Feed for the Digital Edition of MSDN Magazine - July 2008

MSDN Magazine - July 2008 Contents Toolbox CLR Inside Out Flex Your Data Data Points Advanced Basics Office Space Cutting Edge Data Services ADO.NET Data and WPF Transactions WCF P2P Test Run Security Briefs Foundations .NET Matters {End Bracket}

MSDN Magazine - July 2008

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