ios 获取当前正在显示的控制器

/**
 获取当前屏幕显示的viewcontroller
 
 @return 当前正在显示的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;
    }
    return result;
}