最好用的擷取目前VC

//擷取目前螢幕顯示的viewcontroller

- (UIViewController *)getCurrentVC

{

    UIViewController *result = nil;

    UIWindow * window = [[UIApplication sharedApplication] keyWindow];

    //app預設windowLevel是UIWindowLevelNormal，如果不是，找到UIWindowLevelNormal的

    if (window.windowLevel != UIWindowLevelNormal)

    {

        NSArray *windows = [[UIApplication sharedApplication] windows];

        for(UIWindow * tmpWin in windows)

        {

            if (tmpWin.windowLevel == UIWindowLevelNormal)

            {

                window = tmpWin;

                break;

            }

        }

    }

    id  nextResponder = nil;

    UIViewController *appRootVC=window.rootViewController;

    //    如果是present上來的appRootVC.presentedViewController 不為nil

    if (appRootVC.presentedViewController) {

        nextResponder = appRootVC.presentedViewController;

    }else{

        UIView *frontView = [[window subviews] objectAtIndex:0];

        nextResponder = [frontView nextResponder]; 

    }

    if ([nextResponder isKindOfClass:[UITabBarController class]]){

        UITabBarController * tabbar = (UITabBarController *)nextResponder;

        UINavigationController * nav = (UINavigationController *)tabbar.viewControllers[tabbar.selectedIndex];

        //        UINavigationController * nav = tabbar.selectedViewController ; 上下兩種寫法都行

        result=nav.childViewControllers.lastObject;

    }else if ([nextResponder isKindOfClass:[UINavigationController class]]){

        UIViewController * nav = (UIViewController *)nextResponder;

        result = nav.childViewControllers.lastObject;

    }else{

        result = nextResponder;

    }

    return result;

}