Question

I’ve enabled ARC, In my didFinishLaunchingWithOptions method, I wrote the following code:

AppDelegate.h:

@interface AppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) UIWindow *window;

@property (strong, nonatomic) ViewController *viewController;

@end

AppDelegate.m:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    // Override point for customization after application launch.
    ViewController * vc = [[ViewController alloc] initWithNibName:@"ViewController" bundle:nil];
    UINavigationController * nav = [[UINavigationController alloc] initWithRootViewController:vc];
    self.viewController = nav;
    self.window.rootViewController = self.viewController;
    [self.window makeKeyAndVisible];
    return YES;
}

But the statement: self.viewController = nav; gets a compile warning, the warning info is:

file://.../AppDelegate.m: warning: Semantic Issue: Incompatible pointer types passing 'UINavigationController *__strong' to parameter of type 'ViewController *'


How to remove the warning?

Thanks.

Answer 1

I assume that ViewController is a custom subclass of UIViewController which is either completely different or a subclass of UINavigationController itself. That’s why it’s wrong: a superclass can’t completely act as it’s subclass(es) (e. g., it may not have certain properties/methods etc.), hence the warning.