Introducing ASP.NET AJAX in .NET

Encoder PDF-417 2d barcode in .NET Introducing ASP.NET AJAX

The flexible design of the architecture naturally provides two development scenarios. The first scenario is primarily implemented on the client side and is known as the client-centric development model. The second is developed mainly on the server side and is identified as the server-centric development model. It s worth taking some time to understand how these models work and when to use each of them. In the client-centric model, the presentation tier is driven from the client-script using DHTML and JavaScript. This means a smarter and more interactive application is delivered from the server to the browser when the page is first loaded. Afterward, interaction between the browser application and the server is limited to retrieving the relevant data necessary to update the page. This model encourages a lot more interactivity between the user and the browser application, resulting in a richer and more intuitive experience. Figure 1.7 illustrates the client-centric development model. The client-centric model is also ideal for mashups and applications that wish to fully exploit all the features DHTML has to offer.

A mashup is a web application that consumes content from more than one external source and aggregates it into a seamless, interactive experience for the user.

You ll build a simple mashup in chapter 5, once you ve delved deeper into the networking components of the framework. In the meantime, Pageflakes.com provides an excellent example of the rich content mashups can consume (see figure 1.8).

Figure 1.7 The client-centric development model is driven by a smarter and more interactive application that runs on the browser.

Figure 1.8 Pageflakes is a great example of how a mashup application consumes data from multiple resources to enrich the user experience.

An application like Pageflakes relies heavily on user interaction. In addition, the page needs to be light, effective, and mindful of system resources. For these reasons, a client-centric approach is the preferred model.

In the server-centric model, the application logic and most of the UI rationale remain on the server. Incremental changes for the UI are passed down to the browser application instead of the changes being made from the client-side script. This approach resembles the traditional ASP.NET page model, where the server renders the UI on each postback and sends back down to the browser a new page to render. The difference between this model and the traditional model in ASP.NET is that only the portions of the UI that need to be rendered are passed down to the browser application, rather than the whole page. As a result, interactivity and latency are both improved significantly. Figure 1.9 illustrates the nature of the server-centric development model.

Figure 1.9 The Server-Centric Development model passes down to the browser application portions of the page to update instead of a whole new page to refresh.

This approach appeals to many ASP.NET developers because it grants them the ability to keep the core UI and application logic on the server. It s also attractive because of its transparency and ability to behave as a normal application if the user disables JavaScript in the browser. When you re working with controls like the GridView and Repeater in ASP.NET, the server-centric model offers the simplest and most reliable solution.

After examining the architecture and features in the framework, you can easily deduce the goals and intentions that ASP.NET AJAX sets out to accomplish:

Easy-to-use, highly productive framework The main objective is to simplify the efforts of adding Ajax functionality to web applications. This is accomplished by providing a rich client library and a comprehensive set of server controls that are easy to use and integrate into existing applications. Server programming model integration Server controls provide ASP.NET developers with a familiar paradigm for developing web applications. These controls emit the JavaScript needed to Ajax-enable a page with little effort or knowledge of JavaScript and the XMLHttpRequest object. World-class tools and components Components and tools built on top of the framework not only extend the framework but also provide the development community with a rich collection of tools to leverage and build on. This includes tools for debugging, tracing, and profiling. Cross-platform support Support for Internet Explorer, Firefox, Safari, and Opera extracts away the hassle of dealing with browser differences and discrepancies.