MSDN Magazine - July 2008 - (Page 56)

ment on the service that is highlighted by the input adapter service in Figure 6. The method referenced through the ServiceMethod attribute is required to have the following prototype: string MethodName(string contextKey); The contextKey parameter can contain any data serialized in any format that the service method knows how to process. In an input adapter service class, you take the input string and transform it into more specific parameters that other classes in the service know how to process. One of the issues you may run into when using the extender is that it doesn’t prevent the default event when the user clicks a button. So if the button is an ASP.NET button, the postback still occurs, which invalidates the service call. Here’s a more common way of using the DynamicPopulate extender: The attached JavaScript simple functions does the following: Figure 8 Executing an HTML Message Pattern function invoke() { var extender = $find("DynamicPopulateExtender1"); var isOffline = $get("chkOffline").checked; extender.populate(isOffline.toString()); } same IIS application that hosts the AJAX service layer. These pages will be invoked programmatically and the markup they return will be forwarded to the client. The HTML Message pattern tends to generate more traffic than plain calls going to a service that returns raw data. It should be noted, though, that the HTML Message pattern results in less traffic than partial rendering. The more you add styles and HTML enhancements, the larger the size of the packet you return grows. In light of this, you can decouple HTML styling from HTML layout and embed in the markup only references to client-side CSS classes for styling. If you reduce the HTML markup to just layout and data, the percentage of the extra stuff that is transferred beyond raw data may be significantly lower. During my experiments, I noted that a page built with HTML Message may sometimes result in even lower traffic than a page built with BST if you only need to display a few fields and you limit yourself to referencing CSS client classes for styling. Based on this code, the UI is updated by merging the HTML response with the element specified through the TargetControlID property of the extender. Solutions for Now DynamicPopulate Extender To wrap up, I’d like to spend some time on one of the extenders available in the AJAX Control Toolkit—the DynamicPopulate extender that goes well with an HTML Message service. When bound to a client trigger control (say, a button), the extender invokes a service method and attaches the results to the innerHTML property of a DOM element. Needless to say, the DynamicPopulate extender requires an HTML Message service in the AJAX service layer: HTML is used for presentation whereas XML, JSON, and RSS are formats that move server-generated data to the client where it can be manipulated for presentation. In the context of AJAX, this neat model is hindered by the use of the JavaScript language. Once you have downloaded data to the client, you only have JavaScript to build the UI. The BST pattern in the form of custom data binding and template techniques helps you create the UI you need. What if you have a server-centric mindset and just hate JavaScript? What if the UI is particularly complex and you prefer to use more reliable and powerful development and debugging tools? What if both on the server and the client you end up duplicating the same heavyweight algorithm on some large data structure? Wouldn’t an HTML response eliminate some concerns on the client? In general, I believe that until we get a powerful set of controls with a rich client-side object model, we may not always employ the otherwise desirable model in which HTML is used for presentation and JSON is used for data. Today, this model may not be applicable in all situations as far as an AJAX presentation is concerned. That’s why the HTML Message pattern is worth a look. It may not serve all purposes, but it has its place.  Dino Esposito is the author of Programming ASP.NET 3.5 Core Refer- The DynamicPopulate extender also imposes another require56 msdn magazine ences. Based in Italy, Dino is a frequent speaker at industry events worldwide. You can join his blog at weblogs.asp.net/despos. Cutting Edge http://weblogs.asp.net/despos

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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