Touch Events and UIResponder - iOS Programming: The Big Nerd Ranch Guide - page 546

In TouchViewController.m , override loadView to set up an instance of
TouchDrawView as TouchViewController 's view . Make sure to import the
header file for TouchDrawView at the top of this file.
#import "TouchViewController.h"
#import "TouchDrawView.h"
@implementation TouchViewController
- (void)loadView
{
[self setView:[[TouchDrawView alloc] initWithFrame:CGRectZero]];
}
@end
In AppDelegate.m , create an instance of TouchViewController and set it as the
rootViewController of the window. Don't forget to import the header file for
TouchViewController in this file.
#import "AppDelegate.h"
#import "TouchViewController.h"
@implementation AppDelegate
@synthesize window = _window;
- (BOOL)application:(UIApplication *)application
didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
// Override point for customization after application launch.
TouchViewController *tvc = [[TouchViewController alloc] init];
[[self window] setRootViewController:tvc];
self.window.backgroundColor = [UIColor whiteColor];
[self.window makeKeyAndVisible];
return YES;
}