flutter 错误 : The following NoSuchMethodError was thrown building

Question

我是 flutter 的新手，每次运行应用程序时都会出错:

══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
The following NoSuchMethodError was thrown building DataList(dirty, dependencies:
[_InheritedProviderScope<List<Store>>], state: _DataListState#67e37):
The getter 'length' was called on null.
Receiver: null
Tried calling: length
The relevant error-causing widget was:
  DataList

这是我的数据列表文件:

class DataList extends StatefulWidget {
  @override
  _DataListState createState() => _DataListState();
}

class _DataListState extends State<DataList> {
  @override
  Widget build(BuildContext context) {
    final stores = Provider.of<List<Store>>(context);

    // stores.forEach((d) {
    //   print(d.name);
    // });

    return ListView.builder(
      itemCount: stores.length,
      itemBuilder: (context, index) {
        return StoreTile(store: stores[index]);
      },
    );
  }
}

这发生在我登录并显示商店列表之后。我打印了 stores.length 并返回了 6，但无论出于何种原因，应用程序发现了一个 null 并抛出错误。

请注意，应用程序的屏幕显示正确，但在调试控制台中出现此错误。

感谢任何帮助乔

Answer 1

您的提供商似乎需要一点时间来获取商店列表，因此 stores 暂时为空。您可以在 stores 为 null 时显示进度指示器，然后显示数据

class _DataListState extends State<DataList> {
  @override
  Widget build(BuildContext context) {
    final stores = Provider.of<List<Store>>(context);

    // stores.forEach((d) {
    //   print(d.name);
    // });

    return stores == null 
            ? Center(child: CircularProgressIndicator())
            : ListView.builder(
      itemCount: stores.length,
      itemBuilder: (context, index) {
        return StoreTile(store: stores[index]);
      },
    );
  }
}