Dart、Flutter、Future Builder、ListViewBuilder

Question

我有来自 api 的响应，它有 83 个对象，但我的应用程序不会呈现超过 39 个项目，错误 RangeError (index): Invalid value: Valid value range is empty: 0，如果我将 itemCount 替换为 39 工作正常，我哪里出错了？也许是因为我在 initState 中使用了 setState？我无法显示更多代码，因为论坛阻止了它我的代码在这里：

  void initState() {
    super.initState();
    Future.delayed(Duration(seconds: 1), () {
      loadFuture = NetworkUtils.getOrdersByUserId(id);
      NetworkUtils.getOrdersByUserId(id).then((value) {
        setState(() {
          orders = value;
        });
      });
    });
  }
class _OrderPageState extends State<OrderPage> {
  var orders = [];
  Future loadFuture;
  Timer timer;
  


  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Column(
        children: <Widget>[
          SizedBox(
            height: 8,
          ),
          Expanded(
            child: FutureBuilder<dynamic>(
              future: loadFuture,
              builder: (BuildContext context, AsyncSnapshot<dynamic> snapshot) {
                if (snapshot.hasData &&
                    snapshot.connectionState != ConnectionState.waiting) {
                  return ListView.builder(
                    itemCount: orders.length,
                    itemBuilder: (BuildContext context, int index) {
                      return Container(
                        margin:
                            EdgeInsets.symmetric(horizontal: 8, vertical: 6),
                        decoration: BoxDecoration(
                          borderRadius: BorderRadius.circular(5),
                          boxShadow: [
                            BoxShadow(
                              offset: Offset(0, 1),
                              blurRadius: 3,
                              color: Color(0xFF12153D).withOpacity(0.2),
                            ),
                          ],
                        ),
                        
                          child: Text('Here more info ')
                          
                        ),
                      );
                    },
                  );
                } else {
                  //
                }
              },
            ),
          ),
        ],
      ),
    );
  }
}

if itemsCount = orders.length

if itemsCount = 39

Answer 1

您执行了两次查询。

1. loadFuture = NetworkUtils.getOrdersByUserId(id);
2. NetworkUtils.getOrdersByUserId(id).then((value) {});

改成这样：

@override
  void initState() {
    super.initState();
    Future.delayed(Duration(seconds: 1), () {
      loadFuture = NetworkUtils.getOrdersByUserId(id);
      loadFuture.then((value) {
        setState(() {
          orders = value;
        });
      });
    });