Flutter JSON解析与复杂模型转换技巧及实例
其实转换成model类是有好处的，转换后可以减少上线后APP崩溃和出现异常，所以我们从这节课开始，要制作model类模型，然后用model的形式编辑UI界面。
类别json的分析
比如现在从后台得到了一串JSON数据：
{
"code": "0",
"message": "success",
"data": [{
"mallCategoryId": "4",
"mallCategoryName": "白酒",
"bxMallSubDto": [{
"mallSubId": "2c9f6c94621970a801626a35cb4d0175",
"mallCategoryId": "4",
"mallSubName": "名酒",
"comments": ""
}, {
"mallSubId": "2c9f6c94621970a801626a363e5a0176",
"mallCategoryId": "4",
"mallSubName": "宝丰",
"comments": ""
}, {
"mallSubId": "2c9f6c94621970a801626a3770620177",
"mallCategoryId": "4",
"mallSubName": "北京二锅头",
"comments": ""
}, {
"mallSubId": "2c9f6c94679b4fb10167f7cc035c15a8",
"mallCategoryId": "4",
"mallSubName": "大明",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7cc2af915a9",
"mallCategoryId": "4",
"mallSubName": "杜康",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7cc535115aa",
"mallCategoryId": "4",
"mallSubName": "顿丘",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7cc77b215ab",
"mallCategoryId": "4",
"mallSubName": "汾酒",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7cca72e15ac",
"mallCategoryId": "4",
"mallSubName": "枫林",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7cccae215ad",
"mallCategoryId": "4",
"mallSubName": "高粱酒",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7ccf0d915ae",
"mallCategoryId": "4",
"mallSubName": "古井",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7cd1d6715af",
"mallCategoryId": "4",
"mallSubName": "贵州大曲",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7cd3f2815b0",
"mallCategoryId": "4",
"mallSubName": "国池",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7cd5d3015b1",
"mallCategoryId": "4",
"mallSubName": "国窖",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7cd7ced15b2",
"mallCategoryId": "4",
"mallSubName": "国台",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7cd9b9015b3",
"mallCategoryId": "4",
"mallSubName": "汉酱",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7cdbfd215b4",
"mallCategoryId": "4",
"mallSubName": "红星",
"comments": null
}, {
"mallSubId": "2c9f6c946891d16801689474e2a70081",
"mallCategoryId": "4",
"mallSubName": "怀庄",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7cdddf815b5",
"mallCategoryId": "4",
"mallSubName": "剑南春",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7cdfd4815b6",
"mallCategoryId": "4",
"mallSubName": "江小白",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb1016802277c37160e",
"mallCategoryId": "4",
"mallSubName": "金沙",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7ce207015b7",
"mallCategoryId": "4",
"mallSubName": "京宫",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7ce46d415b8",
"mallCategoryId": "4",
"mallSubName": "酒鬼",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb101680226de23160d",
"mallCategoryId": "4",
"mallSubName": "口子窖",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7ce705515b9",
"mallCategoryId": "4",
"mallSubName": "郎酒",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7ce989e15ba",
"mallCategoryId": "4",
"mallSubName": "老口子",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7cec30915bb",
"mallCategoryId": "4",
"mallSubName": "龙江家园",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7cef15c15bc",
"mallCategoryId": "4",
"mallSubName": "泸州",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7cf156f15bd",
"mallCategoryId": "4",
"mallSubName": "鹿邑大曲",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7cf425b15be",
"mallCategoryId": "4",
"mallSubName": "毛铺",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7cf9dc915c0",
"mallCategoryId": "4",
"mallSubName": "绵竹",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7cfbf1c15c1",
"mallCategoryId": "4",
"mallSubName": "难得糊涂",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7cfdd7215c2",
"mallCategoryId": "4",
"mallSubName": "牛二爷",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7cf71e715bf",
"mallCategoryId": "4",
"mallSubName": "茅台",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7d7eda715c3",
"mallCategoryId": "4",
"mallSubName": "绵竹",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7d96e5c15c4",
"mallCategoryId": "4",
"mallSubName": "难得糊涂",
"comments": null
}, {
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"mallCategoryId": "4",
"mallSubName": "牛二爷",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7dae16415c6",
"mallCategoryId": "4",
"mallSubName": "牛栏山",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7db11cb15c7",
"mallCategoryId": "4",
"mallSubName": "前门",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7db430c15c8",
"mallCategoryId": "4",
"mallSubName": "全兴",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7db6cac15c9",
"mallCategoryId": "4",
"mallSubName": "舍得",
"comments": null
}, {
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"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7dc30b815cb",
"mallCategoryId": "4",
"mallSubName": "水井坊",
"comments": null
}, {
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"mallCategoryId": "4",
"mallSubName": "四特",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7dc765c15cd",
"mallCategoryId": "4",
"mallSubName": "潭酒",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7dc988a15ce",
"mallCategoryId": "4",
"mallSubName": "沱牌",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7dcba5a15cf",
"mallCategoryId": "4",
"mallSubName": "五粮液",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7dcd9e815d0",
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"mallSubName": "西凤",
"comments": null
}, {
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"mallSubName": "习酒",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7dd11b215d2",
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"comments": null
}, {
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"mallSubName": "洋河",
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"image": "http://images.baixingliangfan.cn/firstCategoryPicture/20190131/20190131170036_4477.png"
}, {
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"mallCategoryName": "啤酒",
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"mallSubName": "福佳",
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}, {
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"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7f5027a15e3",
"mallCategoryId": "2c9f6c946449ea7e01647ccfddb3001e",
"mallSubName": "饼干",
"comments": null
}, {
"mallSubId": "2c9f6c94679b4fb10167f7f530fd15e4",
"mallCategoryId": "2c9f6c946449ea7e01647ccfddb3001e",
"mallSubName": "冲调",
"comments": null
}, {
"mallSubId": "2c9f6c94683a6b0d016846b49436003b",
"mallCategoryId": "2c9f6c946449ea7e01647ccfddb3001e",
"mallSubName": "休闲水果",
"comments": null
}],
"comments": null,
"image": "http://images.baixingliangfan.cn/firstCategoryPicture/20190131/20190131170200_7553.png"
}, {
"mallCategoryId": "2c9f6c946449ea7e01647cd08369001f",
"mallCategoryName": "粮油调味",
"bxMallSubDto": [{
"mallSubId": "2c9f6c946449ea7e01647dd2e8270043",
"mallCategoryId": "2c9f6c946449ea7e01647cd08369001f",
"mallSubName": "油/粮食",
"comments": ""
}, {
"mallSubId": "2c9f6c946449ea7e01647dd31bca0044",
"mallCategoryId": "2c9f6c946449ea7e01647cd08369001f",
"mallSubName": "调味品",
"comments": ""
}, {
"mallSubId": "2c9f6c946449ea7e01647dd35a980045",
"mallCategoryId": "2c9f6c946449ea7e01647cd08369001f",
"mallSubName": "酱菜罐头",
"comments": ""
}],
"comments": null,
"image": "http://images.baixingliangfan.cn/firstCategoryPicture/20181212/20181212115842_9733.png"
}, {
"mallCategoryId": "2c9f6c9468a85aef016925444ddb271b",
"mallCategoryName": "积分商品",
"bxMallSubDto": [],
"comments": null,
"image": "http://images.baixingliangfan.cn/firstCategoryPicture/20190225/20190225232703_9950.png"
}]
}
模型层的建立
把模型层单独放到一个文件夹里，然后建立一个category.dart文件。这个文件就是要结合json文件，形成的modle文件。文件里大量使用了dart中的 factory语法。
工厂构造函数
factory 关键字的功能，当实现构造函数但是不想每次都创建该类的一个实例的时候使用。
工厂模式是我们最常用的实例化对象模式了，是用工厂方法代替new操作的一种模式。用简单明了的方式解释，模式上类似于面向对象的多态，用起来和静态方法差不多。高雅和低俗的结合，相当于听着贝多芬的交响乐《命运》，看着波多野结衣的岛国小电影，只要你爽，什么都可以。
我们先制作了一个大分类的Class,代码如下：
class CategoryBigModel{
String mallCategoryId; //类别ID
String mallCategoryName; //类型名称
List<dynamic> bxMallSubDto; //子类 dynamic动态的
Null comments; //描述
String image; //图片
//构造函数
CategoryBigModel({
this.mallCategoryId, this.mallCategoryName, this.bxMallSubDto, this.comments, this.image
});
//工厂模式-用这种模式可以省略New关键字
factory CategoryBigModel.fromJson(dynamic json){
return CategoryBigModel(
mallCategoryId: json['mallCategoryId'],
mallCategoryName:json['mallCategoryName'],
bxMallSubDto:json['bxMallSubDto'],
comments:json['comments'],
image:json['image'],
);
}
}
这个只是单个的一个大类信息的模型，但我们是一个列表，这时候就需要制作一个列表的模型，而这个List里边是我们定义的CategoryBigModel模型。简单理解就是先定义一个单项模型，然后再定义个列表的模型。
class CategoryBigListModel {
List<CategoryBigModel> data;
CategoryBigListModel(this.data);
factory CategoryBigListModel.formJson(List json){
return CategoryBigListModel(
json.map((i)=>CategoryBigModel.fromJson((i))).toList()
);
}
}
这样就建立好了一个模型，其实这个模型还可以继续建立，以后的课程中也会逐渐深入。这里到这里，相信大家都掌握了建立模型的方法。
数据模型的使用
使用数据模型就简单很多了。直接声明变量，调用formJson方法就可以了。直接在_getCategory()方法里。记得先引入数据模型类，然后用.的形式进行输出了。
import '../model/category.dart';
void _getCategory() async{
await request('post', 'getCategory').then((val){
var data = json.decode(val.toString());
//print(data);
CategoryBigListModel list = CategoryBigListModel.formJson(data['data']);
list.data.forEach((item) => print(item.mallCategoryName));
});
}
写完这些，你就可以在控制台看到结果了。如果是第一次接触数据模型，可能还是稍微有些绕的。
json_to_dart的使用
如果我们得到一个特别复杂的JSON,有时候会无从下手开始写Model,这时候就可以使用一些辅助工具。我认为json_to_dart是比较好用的一个。它可以直接把json转换成dart类，然后进行一定的修改，就可以快乐的使用了。工作中我拿到一个json，都是先操作一下，然后再改的。算是一个小窍门吧。
地址：https://javiercbk.github.io/json_to_dart/
实例：分类列表
自动生成model模型
改名为CategoryModel
左侧动态菜单的建立
快速建立了一个名字为LeftCategoryNav的StatefulWidget。并声明了一个List数据，起名就叫list。具体代码如下：
//左侧大类导航
class LeftCategoryNav extends StatefulWidget {
_LeftCategoryNavState createState() => _LeftCategoryNavState();
} class _LeftCategoryNavState extends State<LeftCategoryNav> {
List list=[]; @override
Widget build(BuildContext context) {
return Container();
} }
把上面的调用后台类别的方法拷贝到这里，并进行改写。注意这里我们使用了setState来改变lsit 的状态，这样我们从后台获取数据后，页面就会有数据。
void _getCategory()async{
await request('post','getCategory').then((val){
var data = json.decode(val.toString());
//print(data);
CategoryModel category = CategoryModel.fromJson(data);
setState(() {
list = category.data;
});
//list.data.forEach((item)=>print(item.mallCategoryName));
});
}
编写大类子项
把大类里的子项分成一个单独的方法，这样可以起到复用的作用。主要知识点是用模型的形式展示数据。
Widget _leftInkWell(int index){
return InkWell(
onTap: (){},
child: Container(
height: ScreenUtil().setHeight(),
padding: EdgeInsets.only(left: ,top: ),
decoration: BoxDecoration(
color: Colors.white,
border: Border(
bottom: BorderSide(width: ,color: Colors.black12)
)
),
child: Text(list[index].mallCategoryName,style: TextStyle(fontSize: ScreenUtil().setSp())),
),
);
}
完善build方法
当子类别写好后，可以对build方法进行完善，build方法我们采用动态的ListView来写，代码如下：
@override
Widget build(BuildContext context) { return Container(
width: ScreenUtil().setWidth(),
decoration: BoxDecoration(
border: Border(
right: BorderSide(width: ,color: Colors.black12)
)
),
child: ListView.builder(
itemCount: list.length,
itemBuilder:(context,index){
return _leftInkWell(index);
}
),
);
}
我们希望获取数据只在Widget初始化的时候进行，所以再重写一个initState方法。
@override
void initState() {
_getCategory(); //请求接口的数据
super.initState();
}
写完这步，就可以进行预览了，在分类页面也该已经展示出了大类的一个类别列表。
完整代码：
import 'package:flutter/material.dart';
import '../service/service_method.dart';
import 'dart:convert';
import 'package:flutter_screenutil/flutter_screenutil.dart';
import 'package:flutter_easyrefresh/easy_refresh.dart';
import '../model/category.dart'; class CategoryPage extends StatefulWidget {
_CategoryPageState createState() => _CategoryPageState();
} class _CategoryPageState extends State<CategoryPage> {
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(title: Text('商品分类')),
body: Container(
child: Row(
children: <Widget>[
LeftCategoryNav(), ]
)
)
);
} } //左侧大类导航
class LeftCategoryNav extends StatefulWidget {
_LeftCategoryNavState createState() => _LeftCategoryNavState();
} class _LeftCategoryNavState extends State<LeftCategoryNav> {
List list = []; @override
void initState() {
_getCategory(); //请求接口的数据
super.initState();
} @override
Widget build(BuildContext context) { return Container(
width: ScreenUtil().setWidth(),
decoration: BoxDecoration(
border: Border(
right: BorderSide(width: ,color: Colors.black12)
)
),
child: ListView.builder(
itemCount: list.length,
itemBuilder:(context,index){
return _leftInkWell(index);
}
),
);
} Widget _leftInkWell(int index){
return InkWell(
onTap: (){},
child: Container(
height: ScreenUtil().setHeight(),
padding: EdgeInsets.only(left: ,top: ),
decoration: BoxDecoration(
color: Colors.white,
border: Border(
bottom: BorderSide(width: ,color: Colors.black12)
)
),
child: Text(list[index].mallCategoryName,style: TextStyle(fontSize: ScreenUtil().setSp())),
),
);
} void _getCategory()async{
await request('post','getCategory').then((val){
var data = json.decode(val.toString());
//print(data);
CategoryModel category = CategoryModel.fromJson(data);
setState(() {
list = category.data;
});
//list.data.forEach((item)=>print(item.mallCategoryName));
});
} }
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