How to get the Controller that the screen is showing in iOS

1. //Get the ViewController currently displayed by Window  
2. - (UIViewController*)currentViewController{  
3.     //Get the root view of the currently active window  
4.     UIViewController* vc = [UIApplication sharedApplication].keyWindow.rootViewController;  
5.     while (1)  
6.     {  
7.         //According to different page switching methods, gradually obtain the top viewController  
8.         if ([vc isKindOfClass:[UITabBarController class]]) {  
9.             vc = ((UITabBarController*)vc).selectedViewController;  
10.         }  
11.         if ([vc isKindOfClass:[UINavigationController class]]) {  
12.             vc = ((UINavigationController*)vc).visibleViewController;  
13.         }  
14.         if (vc.presentedViewController) {  
15.             vc = vc.presentedViewController;  
16.         }else{  
17.             break;  
18.         }  
19.     }  
20.     return vc;  

}