Changes

The hierarchical structure of a user interface has significant implications for how the views appear and behave. Visually, subviews always appear on top of and within the visual frame of their corresponding parent. The button in the above example, therefore, appears on top of the parent view in the running application. Furthermore, the resizing behavior of subviews (in other words the way in which the views change size when the device is rotated) is defined in relation to the parent view. Superviews also have the ability to modify the positioning and size of their subviews.

If we were to design the above nested view hierarchy in Interface Builder it might appear as illustrated in Figure 17-3.