Question

I have a file named MMAppDelegate.m:

#import "MMAppDelegate.h"

@implementation MMAppDelegate

@synthesize window;
@synthesize viewController;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{

    viewController = [[MainViewController alloc] init];
    [window addSubview:viewController.view];

    // Override point for customization after application launch.
    [window makeKeyAndVisible];
    return YES;
}
//and more standard methods

MMAppDelegate.h:

#import <UIKit/UIKit.h>
#import "MainViewController.h"

@interface MMAppDelegate : UIResponder <UIApplicationDelegate> {
    UIWindow *window;
    MainViewController *viewController;
}

@property (nonatomic, retain) UIWindow *window;
@property (nonatomic, retain) MainViewController *viewController;

@end

MainViewController.m:

#import "MainViewController.h"

@implementation MainViewController

- (void)viewDidLoad {
    NSLog(@"view did load main view controller");
    [super viewDidLoad];

    self.view.backgroundColor = [UIColor redColor];
}

@end

And yet when I run the program, I get a black screen, and the output:

2012-02-12 15:44:48.160 MoreMost[44076:f803] view did load main view controller
2012-02-12 15:44:48.163 MoreMost[44076:f803] Applications are expected to have a root view controller at the end of application launch

What is the problem?

Answer 1

Change this line:

[window addSubview:viewController.view];

to this:

window.rootViewController = viewController;

And you’ll need to create the window, like this:

window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];