Flutter【JSON解析与复杂模型转换】

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手动序列化 JSON

关于json.decode(string) ,可以将Json字符串转化成Map类型
缺点：类型安全、没有自动补全、编译时会有异常

import 'dart:convert';
var str='{"name":"李四"，“age”:20}';  
var result=json.decode(str); // Json字符串转化成Map类型

print(result["age"]); // 如str字符串age是数字/字符串类型，打印出来还是20，存在类型安全
print(result["name~"]); //如没有自动补全的提示，不方面

可以看到，我们这样取值是需要手动的敲字段来获取数据的，一旦字段比较多的话，就很麻烦

通过泛类型序列化Json

// model/FocusModel.dart
class FocusModel {
  String sId;
  String title;
  String status;
  String pic;
  String url;

  FocusModel({this.sId, this.title, this.status, this.pic, this.url});

  FocusModel.fromJson(Map jsonData) { // 命名构造函数（方法），然后给里面的属性进行赋值 this.xxx=xxx
    this.sId = jsonData["_id"];
    this.title = jsonData["title"];
    this.status = jsonData['status'];
    this.pic = jsonData['pic'];
    this.url = jsonData['url'];
  }
}

// 使用
把json字符串转化为map类型，然后把它序列化（FocusModel.fromJson），就可以通过focus.xxx直接获取数据

import '../model/FocusModel.dart';
import 'dart:convert';
var str='{"_id":"1","title":"电脑 ","status":"1"," url":"12" }';  // 可以省略new
var focus=new FocusModel.fromJson(json.decode(str)); 
print(focus.sId);
print(focus.title);

另一个例子：
将map转换model

class CategoryBigModel{
  String mallCategoryId;//类别编号
  String mallCategoryName;//类别名称
  List bxMallSubDto;//不知道具体模型就用dynamic类型 ( dynamic 动态类型 )
  Null comments;
  String image;

  //构造方法
  CategoryBigModel({
    this.mallCategoryId,
    this.mallCategoryName,
    this.bxMallSubDto,
    this.comments,
    this.image
  });
  //工厂类的构造方法,就是我常用的实例化对象模式，好处是我们调用这个类的时候不用再使用new关键字了
  //相当于java里面的多态，用起来和我们的静态方法是一样的
  factory CategoryBigModel.formJson(dynamic json){
    return CategoryBigModel(
      mallCategoryId:json['mallCategoryId'],
      mallCategoryName:json['mallCategoryName'],
      bxMallSubDto:json['bxMallSubDto'],
      comments:json['comments'],
      image:json['image']
    );
  }
}

//列表的model
class CategoryBigListModel{
  List data;
  CategoryBigListModel(this.data);

  factory CategoryBigListModel.fromJson(List json){
    return CategoryBigListModel(
      json.map((i)=>CategoryBigModel.formJson((i))).toList()
    );
  }
}

①创建CommonModel 里面有变量、属性
②设置构造方法
③提供工厂方法 fromJson ，里面接收Map类型的json，在里面取出json的值，将它转化成model final类型要return，非则不用

用工具转化

在Android原生开发中，我们有很好用的Gson、FastJson等第三方库来帮助我们将json转成实体类。但是，在Flutter中可能不会有这样的第三方库供我们使用了，详细原因请看 JSON and serialization
https://blog.csdn.net/yuzhiqiang_1993/article/details/88533166

Json数据转成实体类的好处：
将Json数据转成实体类可以方便我们开发的时候使用数据，手动输入字段名称的话很容易出错，并且接口多的话很不好维护。

首先，您需要将字符串解析为更易于管理的 JSON 表示形式。然后，您必须将该表示形式转化为模型或其他一些强类型变量，如此一来，您就可以有效地使用这些字符串。

格式化
http://www.bejson.com/
转换
https://javiercbk.github.io/json_to_dart/

{"code":"0","message":"success","data":[{"image":"http://images.baixingliangfan.cn/compressedPic/20190116145309_40.jpg","oriPrice":2.50,"presentPrice":1.80,"goodsName":"哈尔滨冰爽啤酒330ml","goodsId":"3194330cf25f43c3934dbb8c2a964ade"},{"image":"http://images.baixingliangfan.cn/compressedPic/20190115185215_1051.jpg","oriPrice":2.00,"presentPrice":1.80,"goodsName":"燕京啤酒8°330ml","goodsId":"522a3511f4c545ab9547db074bb51579"},{"image":"http://images.baixingliangfan.cn/compressedPic/20190121102419_9362.jpg","oriPrice":1.98,"presentPrice":1.80,"goodsName":"崂山清爽8°330ml","goodsId":"bbdbd5028cc849c2998ff84fb55cb934"},{"image":"http://images.baixingliangfan.cn/compressedPic/20180712181330_9746.jpg","oriPrice":2.50,"presentPrice":1.90,"goodsName":"雪花啤酒8°清爽330ml","goodsId":"87013c4315e54927a97e51d0645ece76"},{"image":"http://images.baixingliangfan.cn/compressedPic/20180712180233_4501.jpg","oriPrice":2.50,"presentPrice":2.20,"goodsName":"崂山啤酒8°330ml","goodsId":"86388a0ee7bd4a9dbe79f4a38c8acc89"},{"image":"http://images.baixingliangfan.cn/compressedPic/20190116164250_1839.jpg","oriPrice":2.50,"presentPrice":2.30,"goodsName":"哈尔滨小麦王10°330ml","goodsId":"d31a5a337d43433385b17fe83ce2676a"},{"image":"http://images.baixingliangfan.cn/compressedPic/20180712181139_2653.jpg","oriPrice":2.70,"presentPrice":2.50,"goodsName":"三得利清爽啤酒10°330ml","goodsId":"74a1fb6adc1f458bb6e0788c4859bf54"},{"image":"http://images.baixingliangfan.cn/compressedPic/20190121162731_3928.jpg","oriPrice":2.75,"presentPrice":2.50,"goodsName":"三得利啤酒7.5度超纯啤酒330ml","goodsId":"d52fa8ba9a5f40e6955be9e28a764f34"},{"image":"http://images.baixingliangfan.cn/compressedPic/20180712180452_721.jpg","oriPrice":4.50,"presentPrice":3.70,"goodsName":"青岛啤酒11°330ml","goodsId":"a42c0585015540efa7e9642ec1183940"},{"image":"http://images.baixingliangfan.cn/compressedPic/20190121170407_7423.jpg","oriPrice":4.40,"presentPrice":4.00,"goodsName":"三得利清爽啤酒500ml 10.0°","goodsId":"94ec3df73f4446b5a5f0d80a8e51eb9d"},{"image":"http://images.baixingliangfan.cn/compressedPic/20180712181427_6101.jpg","oriPrice":4.50,"presentPrice":4.00,"goodsName":"雪花勇闯天涯啤酒8°330ml","goodsId":"d80462faab814ac6a7124cec3b868cf7"},{"image":"http://images.baixingliangfan.cn/compressedPic/20180717151537_3425.jpg","oriPrice":4.90,"presentPrice":4.10,"goodsName":"百威啤酒听装9.7°330ml","goodsId":"91a849140de24546b0de9e23d85399a3"},{"image":"http://images.baixingliangfan.cn/compressedPic/20190121101926_2942.jpg","oriPrice":4.95,"presentPrice":4.50,"goodsName":"崂山啤酒8°500ml","goodsId":"3758bbd933b145f2a9c472bf76c4920c"},{"image":"http://images.baixingliangfan.cn/compressedPic/20180712175422_518.jpg","oriPrice":5.00,"presentPrice":4.50,"goodsName":"百威3.6%大瓶9.7°P460ml","goodsId":"dc32954b66814f40977be0255cfdacca"},{"image":"http://images.baixingliangfan.cn/compressedPic/20180717151454_4834.jpg","oriPrice":5.00,"presentPrice":4.50,"goodsName":"青岛啤酒大听装500ml","goodsId":"fc85510c3af7428dbf1cb0c1bcb43711"},{"image":"http://images.baixingliangfan.cn/compressedPic/20180712181007_4229.jpg","oriPrice":5.50,"presentPrice":5.00,"goodsName":"三得利金纯生啤酒580ml 9°","goodsId":"14bd89f066ca4949af5e4d5a1d2afaf8"},{"image":"http://images.baixingliangfan.cn/compressedPic/20190121100752_4292.jpg","oriPrice":6.60,"presentPrice":6.00,"goodsName":"哈尔滨啤酒冰纯白啤（小麦啤酒）500ml","goodsId":"89bccd56a8e9465692ccc469cd4b442e"},{"image":"http://images.baixingliangfan.cn/compressedPic/20180712175656_777.jpg","oriPrice":7.20,"presentPrice":6.60,"goodsName":"百威啤酒500ml","goodsId":"3a94dea560ef46008dad7409d592775d"},{"image":"http://images.baixingliangfan.cn/compressedPic/20180712180754_2838.jpg","oriPrice":7.78,"presentPrice":7.00,"goodsName":"青岛啤酒皮尔森10.5°330ml","goodsId":"97adb29137fb47689146a397e5351926"},{"image":"http://images.baixingliangfan.cn/compressedPic/20190116164149_2165.jpg","oriPrice":7.78,"presentPrice":7.00,"goodsName":"青岛全麦白啤11°500ml","goodsId":"f78826d3eb0546f6a2e58893d4a41b43"}]}

import 'package:flutter/material.dart';
import '../service/service_method.dart';
import 'dart:convert';
import '../model/category.dart';

class CategoryPage extends StatefulWidget {
  @override
  _CategoryPageState createState() => _CategoryPageState();
}

class _CategoryPageState extends State {
  @override
  Widget build(BuildContext context) {
    _getCategory();
    return Container(
      child:Center(
        child: Text('分类页面'),
      )
    );
  }

  void _getCategory() async{
    var data={
      'categoryId':'4',
      'CategorySubId':"",
      'page':1
    };

    await request('getMallGoods',formData:data).then((val){
      var data=json.decode(val.toString());
      print(data);
      CategoryListModel list= CategoryListModel.fromJson(data);
      // CategoryListModel list= CategoryListModel.fromJson(data['data']);

      // list.data.forEach((item)=>print(item));
       print('1=============>');
       print(list.data[0].goodsName);
    });
  }
}

// model/category.dart
class CategoryListModel {
  String code;
  String message;
  List data;

  CategoryListModel({this.code, this.message, this.data});

  CategoryListModel.fromJson(Map json) {
    code = json['code'];
    message = json['message'];
    if (json['data'] != null) {
      data = new List();
      json['data'].forEach((v) {
        data.add(new CategoryData.fromJson(v));
      });
    }
  }

  Map toJson() {
    final Map data = new Map();
    data['code'] = this.code;
    data['message'] = this.message;
    if (this.data != null) {
      data['data'] = this.data.map((v) => v.toJson()).toList();
    }
    return data;
  }
}

class CategoryData {
  String image;
  double oriPrice;
  double presentPrice;
  String goodsName;
  String goodsId;

  CategoryData(
      {this.image,
      this.oriPrice,
      this.presentPrice,
      this.goodsName,
      this.goodsId});

  CategoryData.fromJson(Map json) {
    image = json['image'];
    oriPrice = json['oriPrice'];
    presentPrice = json['presentPrice'];
    goodsName = json['goodsName'];
    goodsId = json['goodsId'];
  }

  Map toJson() {
    final Map data = new Map();
    data['image'] = this.image;
    data['oriPrice'] = this.oriPrice;
    data['presentPrice'] = this.presentPrice;
    data['goodsName'] = this.goodsName;
    data['goodsId'] = this.goodsId;
    return data;
  }
}

携程笔记