Chapter 4. Controls

Controls are the building blocks of a graphical user interface (GUI). Familiar controls include buttons, checkboxes, list boxes, and so forth. Controls can provide a means for a user to indicate a preference, enter data, or make selections.

There are five types of web controls (each but the first will be covered in detail in this and coming chapters). They are:

HTML controls

The original controls available to any HTML page. These all work in ASP.NET exactly as they work in other web pages. HTML controls will be used where appropriate in this book, but will not be discussed in detail. For a good resource on HTML controls, see HTML: The Definitive Guide, Second Edition, by Chuck Musciano and Bill Kennedy (O'Reilly).

HTML server controls

Based on original HTML controls, but enhanced to enable server-side processing.

Web (ASP) server controls

Server-side controls providing the same functionality as HTML server controls but integrated into the ASP.NET programming model.

Validation controls

Provide a full range of built-in form validation capability. Chapter 8 discusses validation controls.

User controls and custom controls

Controls created by the developer. Chapter 14 discusses user and custom controls.

HTML server controls and ASP controls both offer significant improvements over the old-style HTML controls. These include:

• The ability to automatically maintain state, discussed in detail in Chapter 6.

• ASP.NET detects the level of the target browser. Uplevel DHTML browsers are sent script for client-side processing. On downlevel standard browsers, all processing is done on the server. The appropriate HTML is generated for each browser.

• Use of a compiled language instead of interpreted script, resulting in better performance.

• The ability to bind HTML server controls and ASP controls to a data source (as discussed in Chapter 9).