Chapter 14. Custom and User Controls

Chapter 4 includes a chart of the five types of controls supported in ASP.NET: HTML controls, HTML server controls, web server controls, validation controls, and controls created by the developer. This chapter discusses this last type of control, known as custom controls, and a subset of them called user controls.

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

• By deriving a new custom control from an existing control (e.g., 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 .

Of course, 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 are quite different 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.