Flutter FutureBuilder小部件动态列表长度

Question

我试图在FutureBuilder小部件中创建动态ListView.builder，但无法获得来自异步快照的列表长度。我已经尝试了< code > item count:snapshot . data . length ，但它不起作用。这是我的代码

class FlutterDemo extends StatelessWidget {
  final QuoteStorage storage;

  FlutterDemo({Key key, @required this.storage}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Scrapy on flutter')),
      body: Center(
        child: FutureBuilder(
            future: storage.getQuotes(),
            builder: (context, AsyncSnapshot<Quotes> snapshot) {
              return snapshot.hasData ? ListView.builder(
                itemCount: snapshot.data.lenght,
                itemBuilder: (context, index) {
                  final quotes = snapshot.data;
                  return Card(
                      child: Padding(
                        padding: const EdgeInsets.all(8.0),
                        child: Text(quotes.items[index].quote),
                      ));
                },
              )
                  : const CircularProgressIndicator();
            }),
      ),
    );
  }
}

数据来自课堂语录:

class Quotes extends Items {
  @override
  final List<Quote> items;
  Quotes({
    this.items,
  });

  factory Quotes.fromJson(String str) => Quotes.fromMap(json.decode(str));
  factory Quotes.fromMap(Map<String, dynamic> json) => Quotes(
        items: json["items"] == null
            ? null
            : List<Quote>.from(json["items"].map((x) => Quote.fromMap(x))),
      );
}

并引用用于构建未来的存储类：

class QuoteStorage {
  // ...
  // ...
  Future<Quotes> getQuotes() async {
    final file = await _localFile;
    final contents = await file.readAsString();
    return Quotes.fromJson(contents);
  }
}

如果我不提供动态的项目计数（从URL获取），应用程序正在崩溃。有什么想法吗？

Answer 1

您收到错误，因为您拼写长度错误。

您可以通过更正长度的拼写来修复此问题。用下面的代码替换您的＜code＞flatterdemo

它工作得很好。

class FlutterDemo extends StatelessWidget {
  final QuoteStorage storage;

  FlutterDemo({Key key, @required this.storage}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Scrapy on flutter')),
      body: Center(
        child: FutureBuilder(
            future: storage.getQuotes(),
            builder: (context, AsyncSnapshot<Quotes> snapshot) {
              return snapshot.hasData ? ListView.builder(
                // current the spelling of length here
                itemCount: snapshot.data.length,
                itemBuilder: (context, index) {
                  final quotes = snapshot.data;
                  return Card(
                      child: Padding(
                        padding: const EdgeInsets.all(8.0),
                        child: Text(quotes.items[index].quote),
                      ));
                },
              )
                  : const CircularProgressIndicator();
            }),
      ),
    );
  }
}

我希望这有帮助。