5.4 Summary

By writing your own controls, you can encapsulate pieces of user interface in reusable classes. The level of sophistication of these controls can be anywhere from a single label with some added feature to a feature-rich, fully custom control presenting a detailed interactive view of a complex piece of data (e.g., a drawing editor). The UserControl class lets you create a component by assembling several other controls into one larger control, arranging them with the same editor that you use when designing a form. For more exotic requirements, you can write a full custom control that inherits directly from Control (or ScrollableControl) and manages all aspects of your control's appearance and behavior. Regardless of how you build your control, you must bear in mind the needs of two kinds of user—the end user and the software developer. Confusing the requirements of these two groups of people can lead to poor software design choices.

Most of the time, if you choose to base your control on another control, you should prefer reuse by containment over reuse by inheritance. However, there are situations in which inheritance is the right style of reuse, so we will look at this in the next chapter.