Programming .NET Windows Applications

Containers

Many controls can contain other controls, grouping them. The Form control is the ultimate container, but it serves a larger purpose than just containing other controls. The form is the center of Windows Forms-based applications, having many unique properties and methods that empower the Form control to fulfill its role. These include properties such as AcceptButton, Modal, and WindowState, and methods such as Activate and Close. Chapter 5 covers the Form control thoroughly.

Some controls exist only to fill the role of container. They have very few properties, and all their methods are either inherited or overridden from the Control class. They cannot receive focus, although they may play a role in the tab order. Their sole mission is to group other controls to a common purpose. That purpose may be ergonomic, e.g., using a container control to put a border around several labels and text boxes used for gathering address information. The purpose may also be directly functional, e.g., grouping several radio buttons so they become mutually exclusive.

The two controls that exist only to be containers are GroupBox and Panel. They are similar in purpose, but have some very different features. In short, the GroupBox displays its Text property as a caption. It cannot scroll. The Panel control, on the other hand, can scroll but does not display its Text property and cannot have a caption.

The class hierarchy shown in Figure 13-1 explains this behavior. The GroupBox class is derived ...