Subclassing UIView and UIScrollView - iOS Programming: The Big Nerd Ranch Guide - page 190

This is your first time programmatically creating an instance of a view and adding it as a
subview of another view, but you have been doing the same thing all along in XIB files. In
your XIB files, when you dragged a view from the library onto the canvas, you created the
view instance. When you dragged that view on top of another view, you established a sub-
view/superview relationship between those two views. A view created programmatically
and a view created by loading a XIB file are no different once the application is executing.
When creating a view programmatically, you use alloc and an initializer message like
you would for any other object. The designated initializer of UIView , and thus Hyp-
nosisView , is initWithFrame: . This method takes a CGRect structure as an argu-
ment. This CGRect is the view's frame .
Every view instance has a frame rectangle. A view's frame specifies the view's size and
position relative to its superview. A frame is represented by a CGRect structure and con-
tains the members origin and size ( Figure 6.6 ). These members are also structures.
The origin is of type CGPoint and contains two float members: x and y . The
size is of type CGSize and has two float members: width and height . (A struc-
ture is not an Objective-C object, so you can't send it messages, and you don't declare it
as a pointer.)
Figure 6.6 CGRect
Thus, a view is always a rectangle. Because the HypnosisView 's origin is (160,
240) , its top left corner is 160 points to the right and 240 points down from the top-left
corner of the window (its superview). This places the top-left corner of the Hypnos-