有什么方法可以使Flutter中的功能无法替代？

我有一个class InfoScreen扩展了的BaseInfoScreen。在其中BaseInfoScreen有一个Widget body();，所有子项都可以覆盖。还有一个在Widget banner();中实现的BaseInfoScreen，并且我继承了小部件以使用它，但不能覆盖它（因为它在所有屏幕上都必须相同）。有什么办法可以告诉我Widget banner();不要被压倒吗？我尝试将final和添加const到函数中，但它不允许我这样做。

完整代码示例：

BaseInfoScreen

  abstract class BaseInfoScreen extends StatefulWidget {
    final String title;
  
    BaseInfoScreen({
      Key key,
      this.title,
    }) : super(key: key);
  }
  
  abstract class BaseInfoScreenState<Page extends BaseInfoScreen>
      extends State<BaseInfoScreen> {
  
    bool showFabMenu() => true;
  }
  
  mixin BaseScreen<Page extends BaseInfoScreen> on BaseInfoScreenState<Page> {
  
    @override
    Widget build(BuildContext context) {
      return Scaffold(
        appBar: CoolAppBar(
          title: widget.title,              
        ),
        drawer: Container(
          width: 290,
          child: Drawer(
            child: DrawerMenu(),
          ),
        ),
        body: body(),
        floatingActionButton: showFabMenu() ? FabMenu() : null,
      );
    }
    
  //This should be overridable
  Widget body();

  //This should be usable by widgets that inherit from BaseInfoScreen, but not override it.
  Widget banner() {
    return Container(
      color: Colors.black12,
      padding: const EdgeInsets.all(20),
      child: Row(
        mainAxisSize: MainAxisSize.max,
        crossAxisAlignment: CrossAxisAlignment.center,
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          widget.bannerIconAsset != null
              ? Container(
                  child: Image.asset(
                    widget.bannerIconAsset,
                    width: 36,
                    height: 36,
                    filterQuality: FilterQuality.high,
                    color: Colors.white,
                  ),
                )
              : Container(
                  child: Icon(
                    widget.bannerIconData,
                    size: 36,
                    color: Colors.white,
                  ),
                ),
          SizedBox(width: 20),
          Container(
            constraints: BoxConstraints(
                maxWidth: MediaQuery.of(context).size.width * 0.7),
            child: FittedBox(
              fit: widget.bannerTitle.length > 10
                  ? BoxFit.fitWidth
                  : BoxFit.none,
              child: Text(
                widget.bannerTitle,
                style: TextStyle(
                  fontSize: 28,
                  fontFamily: 'Raleway',
                  fontWeight: FontWeight.bold,
                  color: Colors.white,
                ),
              ),
            ),
          ),
        ],
      ),
    );
  }    

信息屏幕

class InfoScreen extends BaseInfoScreen {
  final String title;

  InfoScreen({
    this.title,
  }) : super(
          title: title,
        );

  @override
  _InfoScreenState createState() =>
      _InfoScreenState();
}

class _InfoScreenState extends BaseInfoScreenState<InfoScreen> with BaseScreen
{
  _InfoScreenState();

  @override
  Widget body() {
     return Column(
       children: [
         //Here I call banner()
         banner(),
         //Here I declare other widgets that are part of the body
       ],
     );
  }
}

我试图尽可能地简化代码，以使其保持简单。也许答案只是“不，不可能”，但我在网上找不到任何东西。