json - 使用Dart语言获取列表中的复杂格式数据

Question

我只是想通过列表中的api获取数据，但是在调试Class '_InternalLinkedHashMap<String, dynamic>' has no instance method 'cast' with matching arguments.时出现异常

这是我的演示json_api。

首先，我为数据创建了模型类，然后根据api数据清除了变量。
然后创建方法以获取Model类对象列表类型的数据。
然后创建Widget树并添加带有列表类型模型类对象的StreamBuilder以显示数据。

CODE:

模型类别:

class Results {
  String kind;
  List<Item> items;
  int totalItems;
  Results({
    this.kind,
    this.items,
    this.totalItems,
  });
  factory Results.fromJson(Map<String, dynamic> json) => new Results(
    kind: json["kind"],
    items: new List<Item>.from(json["items"].map((x) => Item.fromJson(x))),
    totalItems: json["totalItems"],
  );

  Map<String, dynamic> toJson() => {
    "kind": kind,
    "items": new List<dynamic>.from(items.map((x) => x.toJson())),
    "totalItems": totalItems,
  };
}


class Item {
  String id;
  String kind;
  String selfLink;

  Item({
    this.id,
    this.kind,
    this.selfLink,
  });

  factory Item.fromJson(Map<String, dynamic> json) => new Item(
    id: json["id"],
    kind: json["kind"],
    selfLink: json["selfLink"],
  );

  Map<String, dynamic> toJson() => {
    "id": id,
    "kind": kind,
    "selfLink": selfLink,
  };
}

用于在Model类对象列表中获取数据的方法:

Future<List<Results>> fetchData()async{
   List<Results> results = new List<Results>();
   final response = await http.get(url);
   if(response.statusCode == 200 || json !=null){
     List jsonParsed = json.decode(response.body).cast<Map<String, dynamic>>();
     for (int i = 0; i < jsonParsed.length; i++) {
       results.add(new Results.fromJson(jsonParsed[i]));
     }
    return results;
   }else{
     print('Request failed with status: ${response.statusCode}');
     Fluttertoast.showToast(msg: "Request failed with status: ${response.statusCode}");
     throw Exception('Failed to load post');
   }
 }

使用StreamBuilder的我的窗口小部件树:

body:  Center(
       child:FutureBuilder<List<Results>>(
         future:fetchData(),
         builder: (context, snapshot){
           if(snapshot.hasData){
             return 
             //Center(child:Text(snapshot.data.items[0].id) ,);
              ListView.builder(
               itemCount: snapshot.data.length,
               itemBuilder: (context, int i){
                 return Column(
                  children: <Widget>[
                    ListTile(
                     leading: CircleAvatar(
                       child: Text(snapshot.data[i].items[i].id),
                     ),
                     title: Text(snapshot.data[i].totalItems.toString()),
                     subtitle: Text(snapshot.data[i].kind) ,
                    ),
                    Divider(color: Colors.grey,)
                  ],
                 );
               },
             );
           }else if(snapshot.hasError){
             return Center(child: Text("${snapshot.error}"),);
           }else{
             return Center(child: CircularProgressIndicator(),);
           }
         },
       ),
     ),

我在哪里做错了。

Answer 1

试试这个，

Future<Results> fetchData() async {
    Results results = new Results();
    final response = await http
        .get('https://www.googleapis.com/books/v1/volumes?q=%7Bhttp%7D');
    if (response.statusCode == 200 || json != null) {
      Map jsonParsed = json.decode(response.body);
      results = Results.fromJson(jsonParsed);
      return results;
    } else {
      print('Request failed with status: ${response.statusCode}');
      throw Exception('Failed to load post');
    }
  }

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    fetchData();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text('Tiitle'),
        ),
        body: Center(
          child: FutureBuilder<Results>(
            future: fetchData(),
            builder: (context, snapshot) {
              if (snapshot.hasData) {
                return
                    //Center(child:Text(snapshot.data.items[0].id) ,);
                    ListView.builder(
                  itemCount: snapshot.data.items.length,
                  itemBuilder: (context, int i) {
                    return Column(
                      children: <Widget>[
                        ListTile(
                          leading: CircleAvatar(
                            child: Text(snapshot.data.totalItems.toString()),
                          ),
                          title: Text(snapshot.data.items[i].id),
                          subtitle: Text(snapshot.data.items[i].kind),
                        ),
                        Divider(
                          color: Colors.grey,
                        )
                      ],
                    );
                  },
                );
              } else if (snapshot.hasError) {
                return Center(
                  child: Text("${snapshot.error}"),
                );
              } else {
                return Center(
                  child: CircularProgressIndicator(),
                );
              }
            },
          ),
        ));
  }