问如何计算点指示器的横幅/页数？我使用的是smooth_page_indicator包，可以在pub.dev上使用

EN

class _BannerWidgetState extends State<BannerWidget> {
  int _pages = 0; 
  final _controller = PageController();
  @override
  Widget build(BuildContext context) {
    return Stack(
      children: [
        Padding(
          padding: const EdgeInsets.fromLTRB(10, 0, 10, 10),
          child: ClipRRect(
            borderRadius: BorderRadius.circular(5),
            child: Container(
              height: 140,
              width: MediaQuery.of(context).size.width,
              color: Colors.white,
              child: PageView(
                controller: _controller,
                onPageChanged: ((val) {
                  setState(() {
                    _pages = val.toInt();
                  });
                }),
                children: const [
                  Center(
                    child: Text(
                      'Banner 1',
                      style: TextStyle(fontSize: 20),
                    ),
                  ),
                  Center(
                    child: Text(
                      'Banner 2',
                      style: TextStyle(fontSize: 20),
                    ),
                  ),
                  Center(
                    child: Text(
                      'Banner 3',
                      style: TextStyle(fontSize: 20),
                    ),
                  ),
                  
                ],
              ),
            ),
          ),
        ),
        DotsIndicatorWidget(pages: _pages),
      ],
    );
  }
}

class DotsIndicatorWidget extends StatelessWidget {
  const DotsIndicatorWidget({
    Key? key,
    required int pages,
  })  : _pages = pages,
        super(key: key);

  final int _pages;

  @override
  Widget build(BuildContext context) {
    return Positioned.fill(
      bottom: 18,
      child: Align(
        alignment: Alignment.bottomCenter,
        child: Row(
          //mainAxisSize: MainAxisSize.min,
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            AnimatedSmoothIndicator(
              activeIndex: _pages,
              count: 3,
              effect: const WormEffect(
                  spacing: 4.0,
                  activeDotColor: Colors.green,
                  dotColor: Colors.grey,
                  dotHeight: 8.0,
                  dotWidth: 8.0,
                  radius: 3,
                  type: WormType.normal),
            ),
          ],
        ),
      ),
    );
  }
}