iOS: circular dependency to call method in each other class

I'm trying to implement circular dependency between my appDelegate and my viewController to call methods from my appDelegate to my viewController but is not working.

Here is my implementation appDelegate.h:

@class ViewController;
@interface AppDelegate : UIResponder <UIApplicationDelegate>
@property (strong,nonatomic) ViewController *mainView;

appDelegate.m:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    return YES;
}

- (BOOL)application:(UIApplication *)app
            openURL:(NSURL *)url
            options:(NSDictionary<UIApplicationOpenURLOptionsKey,id> *)options
{
        [self.mainView doSomething];
    return YES;
}

Here is my implementation on my viewController .h:

#import <UIKit/UIKit.h>
@class AppDelegate;

@interface ViewController : UIViewController
@property (strong,nonatomic) AppDelegate *delegate;

-(void)doSomething;

viewcontroller.m:

- (void)viewDidLoad {
    [super viewDidLoad];
    self.delegate = (AppDelegate*)[[UIApplication sharedApplication]delegate];
}

-(void)doSomething
{
    NSLog(@"doing something");
}

I don't have any errors or warnings but the method doSomething is never been call. any of you knows why or what I'm doing wrong?

I'll really appreciate your help.

from iOS: circular dependency to call method in each other class