在Flutter中从JSON创建列表 [英] Creating a list from JSON in Flutter

问题描述

下面的在线示例中，我有以下代码：

Following an online example I have the following code:

_fetchData() async {
    setState(() {
      isLoading = true;
    });

    final response = await http.get(
        "https://apiurl...");

    if (response.statusCode == 200) {
      print(json.decode(response.body).runtimeType); // _InternalLinkedHashMap<String, dynamic>

      list = (json.decode(response.body) as List)
          .map((data) => Model.fromJson(data))
          .toList();

      setState(() {
        isLoading = false;
      });
    } else {
      throw Exception('Failed to load');
    }
  }

哪个会返回此错误：

Unhandled Exception: type '_InternalLinkedHashMap<String, dynamic>' is not a subtype of type 'List<dynamic>' in type cast

这是API的响应：

{"results":[{"docid":"123434","title":"A title"}, ...]}

型号：

class Model {
  final String title;
  final String docid;

  Model._({this.title, this.docid});

  factory Model.fromJson(Map<String, dynamic> json) {
    return new Model._(
      title: json['title'],
      docid: json['docid'],
    );
  }
}

我了解以上工厂期望的论点是是 Map< String，dynamic> ，并且json的格式是不同的，可以更改，但是想知道如何使它与这种格式一起使用。

I understand that the above factory is expecting the argument to be Map<String, dynamic> and the format of the json is different and can be changed, but want to know how to make it work with this format.

***编辑

工作列表视图

body: Column(
    children: <Widget>[
      Padding(
        padding: EdgeInsets.all(10.0),
        child: TextField(
          onChanged: (value) {
            ...
          },
          controller: _searchController,
          decoration: InputDecoration(

          ...
          ),
        ),
      ),
      Expanded(
        child: SizedBox(
          height: 200.0,
          child: ListView.builder(
              itemCount: list.length,
              itemBuilder: (BuildContext context, int index) {
                return Text(list[index].title);
              }),
        ),
      )
    ],
  ),

推荐答案

print（json.decode（response.body）.runtimeType）打印 _InternalLinkedHashMa的原因p 是因为json的顶层确实是一个地图； {结果：[用大括号打开。

The reason that print(json.decode(response.body).runtimeType) prints _InternalLinkedHashMap is because the top level of your json is indeed a map; {"results":[ opens with a brace.

因此， json.decode （response.body）不是列表，不能转换为一个。另一方面， json.decode（response.body）['结果'] 是一个列表。

So, json.decode(response.body) isn't a list and cannot be cast to one. On the other hand, json.decode(response.body)['results'] is a list.

您需要：

  list = json.decode(response.body)['results']
      .map((data) => Model.fromJson(data))
      .toList();

这篇关于在Flutter中从JSON创建列表的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！