Web Control Enhancements in ASP.NET 2.0

I’m sure by now you’ve read more than your share of books and articles describing new ASP.NET 2.0 features. Master pages, themes, providers, etc., are all great, but have you read anything regarding custom Web control development and what has changed in 2.0? Well that’s what I’m here to tell you. If you’ve become involved in control development, either through my articles or on your own, I’ll describe some very cool enhancements that you can put to work right away in your controls using ASP.NET 2.0.

This article assumes a basic knowledge of custom Web control development as explained in my two-part article series, “Custom Web Controls Demystified” published in the Sept/Oct 2005 and Nov/Dec 2005 issues of CoDe Magazine. In this article, I’ll enhance the EmailContact control that I built in the second part of that article.

Ok, so before you misinterpret the title of this article or make any false assumptions about code compatibility, let me start by telling you that all of the Web controls you developed in ASP.NET 1.1 (or 1.0) will work just fine in 2.0. Feel better? Good. Microsoft has not changed anything that will break your existing code. Everything that I will teach you here involves new and exciting technologies that you can add to existing controls or use with new ones.

New Enhancements

Table 1 describes several of the most important enhancements for custom Web control development. These are the ones I will cover in this article, but if you choose to research this topic further, you’ll find that there are several other changes and enhancements in the Web control arena, including Control Adapters, several base classes, region editing, and others. Perhaps I will make some of them the topics of future articles.

Enhancing an Old Friend

In my two-part article series called “Custom Web Controls Demystified” I developed a custom Web control named EmailContact (Figure 1) and allowed you to provide your sites with a “contact us” form, complete with e-mailing functionality. In this article, I’ll enhance that control with the functionality I’ve summarized above.

If you have not read the previous articles, I strongly recommend that you do so in order to familiarize yourself with this control. If you’re a seasoned Web control developer, you should have no trouble following along.

A New Base Class

For a while now, developers have used the WebControl class to derive their visual Web controls. I say “visual” because controls that do not render anything to the browser are typically derived from the Control class. This has not changed and you should continue to use the Control class for any controls that perform invisible functionality or render anything else other than visual HTML to the browser. You should also continue using the WebControl class for any controls you develop using the rendering technique. However, most of us develop composite controls in order to leverage the power of existing controls. In this case, you’ve always inherited from the WebControl class, but you’ve also been forced to remember a few other details and if you forget them, that has always caused a lot of grief.

Composite controls must implement the INamingContainer interface and simply needs to be included by your control class, and forgetting to do so causes all sorts of problems. This interface ensures unique tag naming in all the HTML tags that your control and any controls in its control hierarchy may render. This is crucial in case you have more than one composite control of the same type on a single page. In such a case, you need to ensure that any child elements render with unique names.

Prior to ASP.NET 2.0, composite control developers also needed to remember to call EnsureChildControls in the Render method of a control. If you read back in the previous articles, I showed you how to override the Render method and make this call just before calling the Render method of the base class. This step is necessary in order for the control to render correctly in the design surface of Visual Studio. Forgetting this detail caused some inconvenience.

These two steps were so common in composite controls that many developers had a base class that included these two details and developers derived all of their new composite controls from this base class. ASP.NET 2.0 offers the [appropriately named] CompositeControl. Use this class to build your composite controls and you’ll never again have to remember to implement INamingContainer or perform an EnsureChildControls call from the Render method.

There are a couple of other new base classes that deal with data bound controls and so forth, but I’ll make them the topic of a future article on data binding custom controls. (Are you salivating yet?)

By: Miguel Castro

Miguel is an architect with IDesign who specializes in architecture consulting and building .NET solutions. He is a Microsoft MVP and INETA speaker and has been a software developer for over 22 years. With a Microsoft background that goes all the way back to VB 1.0 (and QuickBasic in fact), Miguel jumped on .NET as soon as the first public Beta was released and has provided .NET solutions for clients around the country in a variety of industries. He considers himself to be a .NET Developer and Architect and has equal love for both VB and C#, and no tolerance for language bigotry. He’s spoken at numerous user groups around the country as well as developer conferences.

He’s the author of the CodeBreeze code-generator, which among things can be found on his Web site:

www.steelbluesolutions.com

Miguel currently lives in Lincoln Park, NJ with his wife Elena and his daughter Victoria.

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