android - 获取 Json 后无法刷新列表视图

Question

我一直在尝试从服务器获取数据并将其显示在 futurebuilder 内的 listview.builder 中，但 listview 仅在应用 setstate() 后才更新，请帮助已经卡了一段时间。

  Future<dynamic> _fetchData() async {
    sPref.getUserId().then((onValue) {
      userIds = onValue;
    });
    sPref.getAuthToken().then((val) {
      token = val;
      var body = {
        'userId': '$userIds',
      };
      var client = http.Client();    

      var response = http.Request(
          'POST', Uri.parse('http://example.net/api/fetchJson'));    

      response.headers["Authorization"] = "Bearer $token";
      response.bodyFields = body;
      print(response.headers);
      client.send(response).then((response) {
        return http.Response.fromStream(response);
      }).then((res) {
        return res.body;
      }).then((body) {
        return json.decode(body);
      }).then((body) {
        print(body.toString());
        var datas = body['data'];
        if (body['status'] == 'success') {
          list = (datas as List)
              .map((data) => new PosModelData.fromJson(data))
              .toList();
          return list;
        } else {
          print('failed');
        }
      });
      return list;
    });
  }  

这就是我将来要称呼它的地方。需要知道我哪里出错了。

           body: FutureBuilder(
             future: _fetchData(),
             builder: (context, data) {
               switch (data.connectionState) {
                 case ConnectionState.none:
                 case ConnectionState.waiting:
                   return Center(child: CircularProgressIndicator());
                 default:
                   // if (data.hasError)
                   //   return new Text('Error: ${data.error}');
                   // else
                   return ListView.builder(
                     itemCount: list.length,
                     itemBuilder: (BuildContext context, int index) {
                       return Container(
                         padding: EdgeInsets.symmetric(
                             horizontal: 6.0, vertical: 4.0),
                         child: Card(
                           elevation: 10.0,
                           child: Column(children: <Widget>[
                             ListTile(
                               title: Text(list[index].firstName),
                               subtitle: list[index].phone != null
                                   ? Text(list[index].phone)
                                   : Text('Not mentioned'),
                               trailing: trailingText(index),
                             ),
                           ]),
                         ),

标签： androiddartflutterflutter-layoutdart-html

Answer 1

在您的代码中，您没有return从您的_fetchData()块中调用。

您的返回类型是Future，您需要使用await，指定您的返回类型List<PosModelData>并return从您的async块中

Future<List<PosModelData>> _fetchData() async {
  final response = await http.Request('POST', Uri.parse('http://example.net/api/fetchJson')); 
  final list = ... convert response to list
  return list;
}

然后你会从回调中得到列表builder: (context, data) {}。

请检查这个例子。

更新 1

除了使用asyncand await，另一种使用方法Future是返回Future类型。指定您的返回类型Future<List< PosModelData>>和返回Future类型

return sPref.then((s) {}.

请查看以下示例代码和Futures 文档以了解 dart 异步编程。

Future<List<PosModelData>> _fetchData() {
  return Future.wait([sPref.getUserId(), sPref.getAuthToken()]).then((data) {
    userIds = data.first;
    token = data[1];

    var body = {
      'userId': '$userIds',
    };
    var client = http.Client();

    var response = http.Request(
        'POST', Uri.parse('http://example.net/api/fetchJson'));

    response.headers["Authorization"] = "Bearer $token";
    response.bodyFields = body;
    print(response.headers);
    return client.send(response).then((response) {
      return http.Response.fromStream(response);
    }).then((res) {
      return res.body;
    }).then((body) {
      return json.decode(body);
    }).then((body) {
      print(body.toString());
      var datas = body['data'];
      if (body['status'] == 'success') {
        list = (datas as List)
            .map((data) => new PosModelData.fromJson(data))
            .toList();
        return list;
      } else {
        print('failed');
      }
    });
  });