Question

我正在尝试创建动态下拉列表，该列表的值是使用微服务从查找表之一填充的，但是直到现在为止我还没有成功地使它起作用。因为我对飞镖/颤振是完全陌生的所以任何人都可以在下面的代码中找出我做错了什么

以下代码用于调用网络服务

Future<List<CountryDropDownList>> getCountriesDetails(String url) async{
    HttpClient httpClient = new HttpClient();
    HttpClientRequest request = await httpClient.getUrl(Uri.parse(url));
    // request.headers.set('content-type', 'application/json');
    print("request data "+request.toString());
    HttpClientResponse microServicesResponse= await request.close();
    String microServicesResponseString = await microServicesResponse.transform(utf8.decoder).join();
    final parsed = await json.decode(microServicesResponseString).cast<Map<String, dynamic>>();
    httpClient.close();
    print("Data Recieved   "+microServicesResponseString.toString());
    return parsed
        .map<CountryDropDownList>(
            (json) => CountryDropDownList.fromJson(json))
        .toList();
  }

这是我的对象类型

class CountryDropDownList{

  String countryName;
  List<StateDropDownList> stateDropDownList;


  CountryDropDownList({this.countryName, this.stateDropDownList});

  factory CountryDropDownList.fromJson(Map<String, dynamic> json) {
    return CountryDropDownList(
      countryName: json['countryName'] as String,
      stateDropDownList: json['states'] as List<StateDropDownList>,
    );
  }
}

，仅用于显示截至目前运行的代码

    class CenterFoundationSubmission extends StatefulWidget  {
      CenterFoundationSubmission({Key key}) : super(key: key);

      @override
      _CenterFoundationSubmissionState createState() => new _CenterFoundationSubmissionState();
    }

    class _CenterFoundationSubmissionState extends State<CenterFoundationSubmission> {

      NetworkUtil _netUtil = new NetworkUtil();

      var url = "SomeUrl";

      @override
      void initState() {
        super.initState();
        setState(() {
        });
      }


      @override
      Widget build(BuildContext context) {
        var futureBuilder = new FutureBuilder(
          future: _getData(),
          builder: (BuildContext context, AsyncSnapshot snapshot) {
            switch (snapshot.connectionState) {
              case ConnectionState.none:
              case ConnectionState.waiting:
                return new Text('loading...');
              default:
                if (snapshot.hasError)
                  return new Text('Exception here is : ${snapshot.error}');
                else
                  return createView(context, snapshot);
            }
          },
        );

        return new Scaffold(
          appBar: new AppBar(
            title: new Text("Center Foundation"),
          ),
          body: futureBuilder,
        );

      }

      Future<List<CountryDropDownList>> _getData() async {
        List<CountryDropDownList> values = new List<CountryDropDownList>();
        values.addAll(_netUtil.getCountriesDetails(url) as List<CountryDropDownList>);

/*Error Added here , i am getting error while casting list to my object type*/


        await new Future.delayed(new Duration(seconds: 10));

        return values;
      }

      Widget createView(BuildContext context, AsyncSnapshot snapshot) {
        List<CountryDropDownList> values = snapshot.data;
        return new ListView.builder(
          itemCount: values.length,
          itemBuilder: (BuildContext context, int index) {
            return new Column(
              children: <Widget>[
                new ListTile(
                  title: new Text(values[index].countryName),
                  subtitle:  new Text(values[index].stateDropDownList[index].statesName),
                  trailing:   new Text(values[index].stateDropDownList[index].districtDropDownList[index].districtsName),
                ),
                new Divider(height: 2.0,),
              ],
            );
          },
        );
      }
    }

我所做的事情我曾尝试通过多种方式调用Web服务，尝试使用JSON字符串响应直接转换服务响应，也许是我尝试过的事情。

请在这里提供帮助，我们将不胜感激。

Answer 1

您可以尝试使用List.from()构造函数吗？这是相同的链接：

https://api.dart.dev/stable/2.8.4/dart-core/List/List.from.html

      stateDropDownList: List<StateDropDownList>.from(json['states']);

List <dynamic>'不是强制类型转换中'List <obj>'类型的子类型

1 个答案: