An Overview of ASP.NET 3.5.

An Overview of ASP.NET 3.5 and Visual Studio 2008
On November 19, 2007, Microsoft officially released the ASP.NET version 3.5 and Visual Studio 2008. Like with the progression from ASP.NET 2.0 to 3.0, the features in ASP.NET 3.5 are additive, meaning that the core assemblies installed from the .NET Framework version 2.0 are still used by the 3.0 and 3.5 versions. The In short, ASP.NET 3.5 doesn't change or take away or break any functionality, concepts, or code present in 2.0 - it simply adds new types and features and capabilities to the framework.
Visual Studio 2008 is the recommended tool for developing ASP.NET applications. Unlike previous versions of Visual Studio, which were targeted to a specific framework version (i.e., Visual Studio .NET 2003 targeted ASP.NET 1.1 and Visual Studio 2005 targeted ASP.NET 2.0), Visual Studio 2008 is multi-targeted, meaning that you choose from a drop-down list whether to have Visual Studio 2008 build applications against the ASP.NET 2.0, 3.0, or 3.5 frameworks. Visual Studio 2008 also includes an improved Designer experience, JavaScript debugging and IntelliSense features, and the ability to view and even step into the core .NET Framework code during debugging.

A new version of the .NET Framework typically involves features that can be divided into one of three categories:

• Framework Features Specific to ASP.NET. These are features that are key to ASP.NET development - new Web controls, for instance. When ASP.NET 2.0 was released, new ASP.NET-specific features included the GridView control and the declarative data binding controls (the SqlDataSource, ObjectDataSource, and so on).
• Framework Features Useful to ASP.NET Developers. This class of features includes those that aren't specific to ASP.NET - they might be used by WinForms developers, too - but are commonly used by developers in building ASP.NET applications. The .NET Framework 2.0 introduced Generics, anonymous types, and improved strongly-typed DataSets, none of which are ASP.NET-specific, but are commonly used by ASP.NET developers.
• Framework Features Not Used by ASP.NET Developers. The .NET Framework includes many classes that are seldom or never used by ASP.NET developers, such as classes in the System.Windows.Forms namespace.

There are three new features worth noting in ASP.NET 3.5:

• Integrated ASP.NET AJAX support,
• The ListView control, and
• The DataPager control

Prior to ASP.NET 3.5, Microsoft's  ASP.NET AJAX  framework  needed to be downloaded and installed as an extension. With ASP.NET 3.5, however, the AJAX-related classes are built directly into the .NET Framework, making it easier to get started building rich, AJAX-enabled Web applications with ASP.NET. (For more information on using the ASP.NET AJAX framework, check out my article series, Building Interactive User Interfaces with Microsoft ASP.NET AJAX.)

ASP.NET 2.0 introduced a number of new data Web controls, including the GridView, DetailsView, and FormView controls. The GridView displays a list of records in a boxy, grid-like table. The DetailsView and FormView each display one record at a time, the DetailsView in a grid-like output and the FormView in a more fluid layout using templates. The ListView control  is an update to the old DataList and Repeater controls, displaying mulitple records and providing functionality like the GridView, but allowing for a more flexible layout through the use of templates. The DataPager Control operates as a sort of free-standing paging interface. In short, it renders a paging user interface - next, previous, first, last buttons, for instance - and is tied to a data Web control. The DataPager only works with those controls that implement the IpageableItemContainer interface, which (currently) includes only the ListView control.

For a step-by-step demo using the ListView and DataPager controls, check out ScottGuthrie’s  blog entry,The<asp:ListView>Control.Microsoft has also published videos showing how to use theListView andDataPager controls.

New Visual Studio 2008 Features
Visual Studio 2008 offers an improved developer experience through a number of new features, including an improved Designer, more modern CSS editing options, and enhanced JavaScript debugging and development support. Visual Studio 2008 can target web applications to the .NET 2.0, .NET 3.0, or .NET 3.5 environments, meaning you can start using Visual Studio 2008 today to work on your ASP.NET 2.0 websites.
Let's look at each of these new features individually.
 
In previous versions of Visual Studio, developers can choose to use the Designer or the Source view when editing the visual component of an ASP.NET page. The Designer provides a WYSIWYG display of the page, whereas the Source view displays the actual markup of the controls. Visual Studio 2008 offers a new Split screen feature, which shows the markup in one pane and the WYSIWYG display in another. When in Split mode, adding content to the Designer automatically updates the markup in the Source view. Unfortunately, the inverse is not true. If you enter new markup manually into the Source view, you either have to save the page or click a button to refresh the Designer view.
With Microsoft's increasing commitment to AJAX, it comes as no surprise that Visual Studio 2008 offers much better JavaScript support. The design- and debug-time experiences have been greatly improved. When writing JavaScript through the Source view, developers are provided with the same level and functionality of IntelliSense support as they are accustomed to when writing server-side code.
Conclusion
The new versions of Visual Studio and ASP.NET add some interesting and overdue features. With ASP.NET 3.5, Microsoft has moved the ASP.NET AJAX framework from a stand-alone extension to part of the .NET Framework, and has rounded out its data Web controls offerrings with the addition of the ListView and DataPager controls. Visual Studio 2008 includes enhancements to the web developer experience, including a richer Designer, enhanced CSS editing capabilities, JavaScript IntelliSense and debugging, and the ability to mutli-target framework versions.