iOS 获取当前正在显示的ViewController

1.我们在非视图类中想要随时展示一个view时，需要将被展示的view加到当前view的子视图，或用当前view presentViewController，或pushViewContrller，这些操作都需要获取当前正在显示的ViewController。

//获取当前屏幕显示的viewcontroller  
- (UIViewController *)getCurrentVC  
{  
    UIViewController *result = nil;  
      
    UIWindow * window = [[UIApplication sharedApplication] keyWindow];  
    if (window.windowLevel != UIWindowLevelNormal)  
    {  
        NSArray *windows = [[UIApplication sharedApplication] windows];  
        for(UIWindow * tmpWin in windows)  
        {  
            if (tmpWin.windowLevel == UIWindowLevelNormal)  
            {  
                window = tmpWin;  
                break;  
            }  
        }  
    }  
      
    UIView *frontView = [[window subviews] objectAtIndex:0];  
    id nextResponder = [frontView nextResponder];  
      
    if ([nextResponder isKindOfClass:[UIViewController class]])  
        result = nextResponder;  
    else  
        result = window.rootViewController;  
    // 显示TabBar的当前显示画面
    if ([result isKindOfClass:[UITabBarController class]])
    {
        UITabBarController *tabBar = (UITabBarController*)result;
        result = tabBar.selectedViewController;
    }
    // 显示Navigation的显示画面
    if ([result isKindOfClass:[UINavigationController class]])
    {
        UINavigationController *navigation = (UINavigationController*)result;
        result = navigation.topViewController;
    }
      return result;
} 

2.获取当前屏幕中present出来的viewcontroller。

- (UIViewController *)getPresentedViewController  
{  
    UIViewController *appRootVC = [UIApplication sharedApplication].keyWindow.rootViewController;  
    UIViewController *topVC = appRootVC;  
    if (topVC.presentedViewController) {  
        topVC = topVC.presentedViewController;  
    }  
      
    return topVC;  
}