User Controls

Deriving from an existing control is one way to reuse it, but the most popular form of reuse for a control is simple containment, as you're accustomed to doing when building custom forms using existing controls. A user control is a way to contain a set of other controls for reuse as a set, producing a kind of “subform.” For example, imagine that we wanted a control that composed our FileTextBox control with a “…” button for browsing. In use, it would look like the one shown in Figure 8.21.

Figure 8.21. A Sample User Control in Action