Each view in a user interface represents a rectangular area of the display. A view is responsible for what is drawn in that rectangle and for responding to events that occur within that part of the screen (such as a touch event).
A user interface screen is comprised of a view hierarchy with a root view positioned at the top of the tree and child views positioned on branches below. The child of a container view appears on top of its parent view and is constrained to appear within the bounds of the parent view’s display area. Consider, for example, the user interface illustrated in Figure 16-1:
In addition to the visible button and checkbox views, the user interface actually includes a number of layout views that control how the visible views are positioned. Figure 16-2 shows an alternative view of the user interface, this time highlighting the presence of the layout views in relation to the child views:
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