Programming ASP.NET, 3rd Edition

Chapter 14. Custom and User Controls

This chapter discusses controls created by the developer. These are called custom controls, and a subset of them is called user controls.

Custom controls are compiled controls that act, from the client’s perspective, much like ASP.NET controls. Custom controls can be created in one of three ways:

• By deriving a new custom control from an existing control (for example, deriving your own specialized text box from asp:textbox). This is known as a derived custom control.

• By composing a new custom control out of two or more existing controls. This is known as a composite custom control.

• By deriving from the base control class, thus creating a new custom control from scratch. This is known as a full custom control.

All three of these methods, and the three control types that correspond to them, are variations on the same theme. We’ll consider these custom controls later in this chapter. The simplest category of custom controls is a subset called user controls. Microsoft distinguishes user controls as a special case because they differ from other types of custom controls. In short, user controls are segments of ASP.NET pages that can be reused from within other pages. This is similar to “include files” familiar to ASP developers. However, user controls are far more powerful. User controls support properties and events and, thus, provide reusable functionality as well as reusable HTML.