iOS 当前控制器

+ (UIViewController *)currentViewController
{
    UIViewController *frontUIViewController = nil;
    UIWindow *defaultWindow = [[UIApplication sharedApplication] keyWindow];
    if (defaultWindow.windowLevel != UIWindowLevelNormal) {
        NSArray *windows = [[UIApplication sharedApplication] windows];
        for(UIWindow *tmpWin in windows) {
            if ([tmpWin isKindOfClass:[UIWindow class]] && tmpWin.windowLevel == UIWindowLevelNormal) {
                defaultWindow = tmpWin;
                break;
            }
        }
    }
    if (defaultWindow && [[defaultWindow subviews] count] > 0) {
        UIView *frontView = [[defaultWindow subviews] objectAtIndex:0];
        id nextResponder = [frontView nextResponder];
        if ([nextResponder isKindOfClass:[UIViewController class]]) {
            frontUIViewController = nextResponder;
        } else {
            frontUIViewController = defaultWindow.rootViewController;
        }
        if (frontUIViewController) {
            frontUIViewController = [self topDisplayViewController:frontUIViewController];
            while (frontUIViewController && frontUIViewController.presentedViewController) {
                frontUIViewController = [self topDisplayViewController:frontUIViewController.presentedViewController];
            }
        }
    }
    return frontUIViewController;
    
}

+ (UIViewController *)topDisplayViewController:(UIViewController *)viewController {
    if ([viewController isKindOfClass:[UINavigationController class]]) {
        return [self topDisplayViewController:[(UINavigationController *)viewController topViewController]];
    } else if ([viewController isKindOfClass:[UITabBarController class]]) {
        return [self topDisplayViewController:[(UITabBarController *)viewController selectedViewController]];
    } else {
        return viewController;
    }
    return nil;
}