WSV 401 - Building Server Controls for ASP.NET Whidbey (Part 1)

Nikhil Kothari discusses Control Building

• Nikhil's demo slides and code are available at http://www.asp.net/whidbey/ as well as on his blog at http://www.nikhilk.net/, where he will post samples of his demo controls that will work with the PDC build of Whidbey as well as with the forthcoming beta release.
• Nikhil started with a demo of the finished control that he's using to demonstrate his points, an HTML Editor control.
• A new base class has been added to the framework called CompositeControl, which encapsulates much of the work for composite controls. This class implements INamingContainer, so you don't have to do that manually anymore. Controls are still added by overriding CreateChildControls.
• New notion is that you override the Render method in composite controls to render layout for your controls.
• Cleaner APIs have been added for sending client-side script to the browser, including referencing a .js file, as well as for common tasks like setting focus on the client side.
• Web resources are a new feature that allow you to package scripts, images, style sheets, and more as assembly resources. Using the Page.GetWebResourceUrl method, you can access these resources programmatically (uses an HttpHandler under the covers). This means that control developers no longer need to ship images, etc. and figure out how to get them installed on the control user's machine. Much less brittle model. Also automatically works at design-time, so images, etc. show up on the design surface in addition to working at runtime.
• Another new feature is script callbacks. Script callbacks allow you to make requests back to the server to retrieve information from the page, without navigating away from the existing page. So you can now update a page seamlessly without postbacks. Script callbacks cause the target page to be instantiated, but it does not go through the entire page lifecycle, only the amount necessary to create and rehydrate its controls, and fire the scriptcallback event. It also solves two problems of postbacks: losing scroll position, and the back button. Because the browser never navigates away from the current page, the user can't use the back button to re-play the interaction.
• Improvements in State Management - Addressing the limitations/issues with ViewState. New feature is Control State...used to store essential information about that control. Control State is separate from ViewState, allowing ViewState to be disabled without breaking controls. Control State is opt-in, so controls must register their interest in maintaining Control State with the page (call Page.RegisterRequiresControlState). Important to keep the information stored as small as possible. The idea is to avoid having Control State become as bloated as ViewState sometimes becomes (such as when using a DataGrid with many rows and columns).
• Adaptive Rendering - Whidbey will provide support for helping control developers to target their controls to multiple browsers and/or devices, using different HtmlTextWriter types and/or Adapters. Nikhil hinted that one possible use of this feature would be to generate XAML from ASP.NET (see, I told you XAML was ASP.NET for Windows guys!). You can write your own custom adapters for devices/browsers you wish to target, if existing adapters don't meet your needs.