flutter 中的一个控制器两个小部件

Question

是否有任何选项可以为两个小部件保留一个控制器？我有 3 个按钮来更改视图，其中两个使用相同的分页控制器，一切正常，直到切换到第三个视图。然后，返回第一或第二视图后，控制器停止工作。

class ViewsScreen extends StatefulWidget {
  const ViewsScreen({Key? key}) : super(key: key);

  @override
  State<ViewsScreen> createState() => _ViewsScreenState();
}

class _ViewsScreenState extends State<ViewsScreen> {
  int _view = 1;
  final _pagingController = PagingController<int, Item>(
    firstPageKey: 1,
  );

  @override
  void dispose() {
    _pagingController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Column(
        children: [
          Container(
            width: double.infinity,
            height: 40,
            child: Row(
              children: [
                _pageButton(Icons.one_k, 'view1', 1),
                _pageButton(Icons.two_k, 'view2', 2),
                _pageButton(Icons.three_k, 'view3', 3),
              ],
            ),
          ),
          Expanded(
              child: _view == 1
                  ? View12(
                      view: 1,
                      controller: _pagingController,
                    )
                  : _view == 2
                      ? View12(
                          view: 2,
                          controller: _pagingController,
                        )
                      : View3()),
        ],
      ),
    );
  }

  Widget _pageButton(IconData icon, String name, int view) {
    return Expanded(
      child: InkWell(
        onTap: () {
          setState(() {
            _view = view;
          });
        },
        child: Row(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Icon(icon),
            Text(name),
          ],
        ),
      ),
    );
  }
}

View12仅根据视图参数改变列表的显示，但使用相同的控制器。

class View12 extends StatefulWidget {
  final int view;
  final PagingController<int, Item> controller;
  const View12(
      {Key? key, required this.view, required this.controller})
      : super(key: key);

  @override
  _View12ViewState createState() => _View12ViewState();
}

class _View12ViewState extends State<View12> {
  @override
  void initState() {
    widget.controller.addPageRequestListener((pageKey) {
      //fetching data from service
      context.read<ViewModel>().fetchPage(pageKey, widget.controller);
    });
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return RefreshIndicator(
      onRefresh: () => Future.sync(
        () => widget.controller.refresh(),
      ),
      child: PagedListView.separated(
        pagingController: widget.controller,
        separatorBuilder: (context, index) =>
            Container(height: 1, color: Colors.black),
        builderDelegate: PagedChildBuilderDelegate<Item>(
          itemBuilder: (context, item, index) {
            if (widget.view == 1)
              return ItemGallery(
                item: item,
              );
            if (widget.view == 2)
              return ItemList(
                item: item,
              );
            return Container();
          },
        ),
      ),
    );
  }
}

获取方法

  Future<void> fetchPage(
      int pageKey, PagingController<int, Offer> controller) async {
    try {
      final newItems = await loadData(pageKey);
      if (isLastPage) {
        controller.appendLastPage(newItems);
      } else {
        final nextPageKey = pageKey + 1;
        controller.appendPage(newItems, nextPageKey);
      }
    } catch (error) {
      controller.error = error;
    }
  }

从view3返回到view12后错误描述：

Answer 1

像这样使用它，

 final PagingController<int, Item> _pagingController =
  PagingController(firstPageKey: 1);

Answer 2

Future<void> _fetchPage(int pageKey) async {
try {
  const _pageSize = 3;
  final newItems =  await loadData(pageKey);
  final isLastPage = newItems.length < _pageSize;
  if (isLastPage) {
    _pagingController.appendLastPage(newItems);
  } else {
    final nextPageKey = pageKey + newItems.length;
    _pagingController.appendPage(newItems, nextPageKey);
  }
} catch (error) {
  _pagingController.error = error;
}

}
方法

像这样改变你的获取