snapshot.data为Null。我正在使用for循环遍历JSON数据并创建对象实例列表

debugcn 发表于 Dev

维沙尔·普拉布（Vishal Prabhu）

我正在从json-generator.com检索json数据，并将其解析以在以下代码中创建公司列表。当我打印JsonData变量时，我可以看到数据，但是snapshot.data为null。这是我的代码

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

class Companies extends StatefulWidget {
  @override
  _CompaniesState createState() => _CompaniesState();
}

class _CompaniesState extends State<Companies> {
  Future<List<Company>> _getCompanies() async {
    var data = await http.get("http://www.json-generator.com/api/json/get/bUYmnsimgi?indent=2");
    var jsonData = json.decode(data.body);

    List<Company> companies = [];
    for (var c in jsonData) {
      Company company = Company(
          c["name"],
          c["opportunites"],
          c["address"],
          c["city"],
          c["state"],
          c["country"],
          c["zipcode"],
          c["phone"],
          c["timezone"],
          c["pipelineRevenue"],
          c["revenueAchieved"],
          c["tags"]);
      companies.add(company);
    }
    return companies;
  }

  @override
  Widget build(BuildContext context) {
    return Container(
        child: FutureBuilder(
            future: _getCompanies(),
            builder: (BuildContext context, AsyncSnapshot snapshot) {
              if (snapshot.hasData) {
                return ListView.builder(
                    itemCount: snapshot.data.length,
                    itemBuilder: (BuildContext context, int index) {
                      return CompanyCardStyle(company: snapshot.data[index]);
                    });
              } else {
                return Center(
                  child: CircularProgressIndicator(),
                );
              }
            }));
  }
}

这是我公司的对象

class Company {
  String name;
  String address;
  int opportunities;
  int pipelineRevenue;
  int revenueAchieved;
  String city;
  String state;
  String country;
  int zipcode;
  double phone;
  String timezone;
  String tags;

  Company(
      this.name,
      this.address,
      this.opportunities,
      this.pipelineRevenue,
      this.revenueAchieved,
      this.city,
      this.state,
      this.country,
      this.zipcode,
      this.phone,
      this.timezone,
      this.tags);
}

我认为for循环存在一些问题，但我无法弄清楚什么是错误的，我是新来解析此类数据的人。

Timilehin Jegede

您做错了一些事情：

来自端点的某些字段输入了错误的信息data type（电话号码为，String但您使用了double。tags也返回了，List但您使用了String。
在将转换jsonData为Company对象时，您将大多数构造函数字段相互交换了。

解：

为您的Company类创建工厂构造函数，以简化json反序列化。您可以查看官方文档中的示例。
为每个字段使用正确的数据类型。

注意：我将tag字段设置为a，String并且仅访问api中列表中的第一个元素。

公司类别

class Company {
  String name;
  String address;
  int opportunities;
  int pipelineRevenue;
  int revenueAchieved;
  String city;
  String state;
  String country;
  int zipcode;
  String phone;
  String timezone;
  String tags;

  Company(
      this.name,
      this.address,
      this.opportunities,
      this.pipelineRevenue,
      this.revenueAchieved,
      this.city,
      this.state,
      this.country,
      this.zipcode,
      this.phone,
      this.timezone,
      this.tags);

  // make a constructor for converting json to a company object
  factory Company.fromJson(Map<String, dynamic> json) {
    return Company(
      json["name"],
      json["address"],
      json["opportunities"],
      json["pipelineRevenue"],
      json["revenueAchieved"],
      json["city"],
      json["state"],
      json["country"],
      json["zipcode"],
      json["phone"],
      json["timezone"],
      json["tags"][0],
    );
  }
}

公司小工具*

class Companies extends StatefulWidget {
  @override
  _CompaniesState createState() => _CompaniesState();
}

class _CompaniesState extends State<Companies> {
  Future<List<Company>> _getCompanies() async {
    var data = await http
        .get("http://www.json-generator.com/api/json/get/bUYmnsimgi?indent=2");
    var jsonData = json.decode(data.body) as List;
    List<Company> companies = [];
    // convert the json to a list of companies
    companies = jsonData
        .map((company) => Company.fromJson(company))
        .toList(); // new line
    print(companies.length);
    return companies;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(
          child: FutureBuilder(
              future: _getCompanies(),
              builder: (BuildContext context, AsyncSnapshot snapshot) {
                if (snapshot.hasData) {
                  return ListView.builder(
                      itemCount: snapshot.data.length,
                      itemBuilder: (BuildContext context, int index) {
                        // use your company card here
                        return Text(
                            'Company $index name: ${snapshot.data[index].name}');
                      });
                } else {
                  return Center(
                    child: CircularProgressIndicator(),
                  );
                }
              })),
    );
  }
}