如何在Flutter中使用json从服务器接收数据

Question

我要在应用程序中使用服务器中的数据。为此，我将使用本地服务器上的json接收数据，但问题是数据为空，并且我的代码未提取该数据。

这是代码：

import 'package:flutter/material.dart';
import 'dart:async';
import 'package:http/http.dart' as http;
import 'dart:convert';
void main() {
  runApp(  MaterialApp(
    home:   MyHomePage(),
  ));
}
class MyHomePage extends StatefulWidget {
  var title;

  MyHomePage({Key key, this.title}) : super(key: key);

  @override
  _MyHomePageState createState() =>   _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {


  Future<Base> _getBase() async {

    var data = await http.get(Uri.encodeFull("http://192.168.1.13:5000/json"));

var jsonData = json.decode(data.body);
Base base =   Base.fromJson(jsonData);
return base;
  }



  @override
  Widget build(BuildContext context) {
    return   Scaffold(
      appBar:   AppBar(
        title:   Text('Hi'),
      ),
      body: Container(
        child: FutureBuilder(
          future: _getBase(),
          builder: (BuildContext context, AsyncSnapshot snapshot) {
            if (snapshot.data == null) {
              return Container(
                child: Center(
                  child: CircularProgressIndicator(
                      valueColor: AlwaysStoppedAnimation<Color>(Colors.teal)),
                ),
              );
            } else {
              return ListView.builder(
                itemCount: snapshot.data.categories.length,
                itemBuilder: (BuildContext context, int index) {
                  return ListTile(
                      subtitle: Text(snapshot.data.categories[index].category_id),
                      title: Text(snapshot.data.categories[index].devices[index].title),
                      leading: CircleAvatar(
                          // ignore: argument_type_not_assignable
                          // backgroundImage:  NetworkImage(snapshot.data.devices[index].thumbnailUrl),
                          )
                          );
                },
              );
            }
          },
        ),
      ),
    );
  }
}

这是用于json的数据模型：

class Base{
  List <Category> array;
  List<Category> categories;
  Base( {this.categories});
  factory Base.fromJson(Map<String,dynamic> parsedJson){
    var list = parsedJson['categories'] as List;
    List<Category> categoryList = list.map((i) => Category.fromJson(i)).toList();
    return Base(
        categories: categoryList
    );

  }

}

class Category {
  int category_id,device_type_id,room_id;
  List<Device_type> device_types;
  List<Rooms> rooms;
  List<Devices> devices;
  Category({this.category_id,this.device_types,this.device_type_id,this.devices,this.rooms,this.room_id});
  factory Category.fromJson(Map<String,dynamic>parsedJson){
    var list1 = parsedJson['Device_types'] as List;
    var list2 = parsedJson['Rooms'] as List;
    var list3 = parsedJson['Devices'] as List;
    List<Device_type> deviceTypeList =list1.map((i)=>Device_type.fromJson(i)).toList();
    List<Rooms> roomsList =list2.map((i)=>Rooms.fromJson(i)).toList();
    List<Devices> devicesList =list3.map((i)=>Devices.fromJson(i)).toList();
    return Category(
        category_id: parsedJson["category_id"],
        device_type_id: parsedJson["device_type_id"],
        room_id: parsedJson["room_id"],
        device_types: deviceTypeList,
        rooms :        roomsList,
        devices:       devicesList

    );
  }

}

class Device_type {
   int device_type_id, image , device_no;
   String title ;


 Device_type ({this.device_type_id,this.title,this.image,this.device_no});
  factory Device_type.fromJson(Map<String,dynamic>parsedJson){
    return Device_type(
      device_type_id: parsedJson["device_type_id"],
      title: parsedJson["title"],
      image: parsedJson["image"],
      device_no: parsedJson["device_no"],
    );
  }



}


class Rooms {
  int id, image , device_no,roomcode;
  String description,title ;
  Rooms ({this.id,this.title,this.image,this.device_no,this.roomcode,this.description});
  factory Rooms.fromJson(Map<String,dynamic> parsedJson){
    return Rooms(
        id: parsedJson["id"],
        title:parsedJson["title"],
        image: parsedJson["image"],
        device_no: parsedJson["device_no"],
        roomcode: parsedJson["roomcode"],
        description: parsedJson["description"]
    );
  }
}


class Devices {
  int device_id, image_path ,type,status,fav_flag, category_id;
  String description,title ;
  Devices ({this.device_id,this.title,this.image_path,
  this.description,this.fav_flag,this.status,this.type,this.category_id});
  factory Devices.fromJson(Map<String,dynamic> parsedJson){
    return Devices(
        device_id: parsedJson["device_id"],
        title:parsedJson["title"],
        image_path: parsedJson["image_path"],
        type: parsedJson["type"],
        status: parsedJson["status"],
        fav_flag: parsedJson["fav_flag"],
        category_id : parsedJson['category_id'],
        description: parsedJson["description"]
    );
  }
}

为了更好地理解，我将图像放在下面：

当我跟踪项目以找出问题所在时，我意识到它只循环了一次，所以数据将永远为空，不知道为什么 任何帮助将不胜感激