未渲​​染数据会产生错误未处理的异常：Flutter中类型'List <dynamic>'不是'Map <dynamic，dynamic>'类型的子类型

Question

我是Flutter的新手。从api提取数据，但是会出现这样的错误，

 [ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled Exception: type 'List<dynamic>' is not a subtype of type 'Map<dynamic, dynamic>'

如果可以的话请给我一个解决方案，然后我接受您的回答这里有人为此提供解决方案吗？提前致谢。这是我的代码。

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'dart:async';
import 'dart:convert';

class DisplayScreen extends StatefulWidget {
  @override
  DisplayScreenState createState() => DisplayScreenState();
}

class DisplayScreenState extends State<DisplayScreen> {
  GlobalKey<FormState> _formKey = GlobalKey<FormState>();
  Map data;
  List userData;


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

  Future fetchPost() async {
    http.Response response = await http.get('http://192.168.1.85:4000/getUser');
    // print(response.body); 
    data = await json.decode(response.body);
    setState(() {
      userData = data["data"];
    });
    debugPrint(userData.toString());
    // return response;
  }

  @override
  Widget build(BuildContext context) {

    return Scaffold(
      appBar: AppBar(
        title: Text('Display'),
      ),
      body: ListView.builder(
        itemCount: userData == null ? 0 : userData.length,
        itemBuilder: (BuildContext context, int index){
          return Card(
            child: Row(
              children: <Widget>[
                Text("${userData[index]["username"]}"),
              ]
            )
          );
        }
      )
    );
  }
}

response.body看起来像

[{"_id":"5da9593ced22552136120d6c","username":"H","email":"H","password":"H","__v":0},{"_id":"5da95d71ed22552136120d6d","email":"happy@gmail.com","password":"happy","username":"happy","__v":0},{"_id":"5da96010ed22552136120d6e","email":"bchdg","password":"ncbfb","username":"vjfj","__v":0},{"_id":"5da96016ed22552136120d6f","email":"chchdy","password":"bcbchf","username":"fhdgd","__v":0},{"_id":"5da9601bed22552136120d70","email":"chxh","password":"ncnc","username":"chdgd","__v":0},{"_id":"5da96021ed22552136120d71","email":"a","password":"a","username":"a","__v":0},{"_id":"5da98b9aba546b42e2d11182","email":"h","password":"h","username":"h","__v":0}]

Answer 1

userData = data["data"];这会尝试将JSON中的“数据”值分配给userData，但JSON中不存在“数据”。您要获取的列表是JSON本身，因此只需将其分配给userData即可：

setState({
  userData = json.decode(response.body);
});

Answer 2

您尝试过类似的方法

Any?

您必须将UserData类定义为类似

Iterable l = json.decode(response.body);
List<UserData> posts = l.map((Map model)=> UserData.fromJson(model)).toList();