Subclassing UIView and UIScrollView - iOS Programming: The Big Nerd Ranch Guide - page 209

In HypnosisterAppDelegate.m , put a super-sized version of HypnosisView in-
side a scroll view and add that scroll view to the window:
- (BOOL)application:(UIApplication *)application
didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
// Override point for customization after application launch.
CGRect screenRect = [[self window] bounds];
// Create the UIScrollView to have the size of the window, matching its size
UIScrollView *scrollView = [[UIScrollView alloc] initWithFrame:screenRect];
[[self window] addSubview:scrollView];