Flutter 中的 JSON 解析，事件分发机制 Android

}

上述代码中，我们创建了一个 List<String> 类型的数组，然后将 List<dynamic> 数组中的元素都添加到了 List<String> 中。输出如下：

flutter: json["cities"] type is List<dynamic>flutter: country name is China

对象嵌套

定义一个 shape.json ，格式如下：

{

"name": "rectangle",

"property": {

"width": 5.0,

"height": 10.0

}

}

实体如下：

class Shape {

String name;

Property property;

Shape({this.name, this.property});

factory Shape.fromJson(Map<String, dynamic> json) {

return Shape(name: json['name'], property: json['property']);

}

}

class Property {

double width;

double height;

Property({this.width, this.height});

factory Property.fromJson(Map<String, dynamic> json) {

return Property(width: json['width'], height: json['height']);

}

}

Service 类如下：

import 'dart:async';

import 'dart:convert';

import 'package:flutter/services.dart';

import '../models/shape.dart';

Future<String> _loadShapeJson() async {

return await rootBundle.loadString('assets/shape.json');

}

Future<Shape> decodeShape() async {

String shapeJson = await _loadShapeJson();

Map<String, dynamic> jsonMap = json.decode(shapeJson);

Shape shape = Shape.fromJson(jsonMap);

print('shape name is ${shape.name}');

return shape;

}

运行之后，会报如下错误：

Unhandled Exception: type '_InternalLinkedHashMap<String, dynamic>' is not a subtype of type 'Property'

也就是说 property: json['property'] 这里赋值的类型是 _InternalLinkedHashMap<String, dynamic> 而不是 Property，json['property'] 的值是这样的 {width: 5.0, height: 10.0}，它是一个 Map ，并不是一个 Property 对象，我们需要先将这个 Map 转化为对象，然后在赋值：

factory Shape.fromJson(Map<String, dynamic> json) {

print('json["property"] is ${json['property']}');

Property property = Property.fromJson(json['property']); // new linereturn Shape(name: json['name'], property: property);

}

输出：

shape name is rectangle

复杂的对象数组嵌套

{"id": "0302","class_name":

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"三年二班","students": [{"name": "叶湘伦","sex": "男"},{"name": "路小雨","sex": "女"}]}

实体：

class ClassInfo {String id;String name;List<Student> studentList;

ClassInfo({this.id, this.name, this.studentList});

factory ClassInfo.fromJson(Map<String, dynamic> json) {return ClassInfo(id: json['id'],name: json['class_name'],studentList: json['students']);}}

class Student {String name;String sex;

Student({this.name, this.sex});

factory Student.fromJson(Map<String, dynamic> json) {return Student(name: json['name'], sex: json['sex']);}}

service:

import 'dart:async';import 'dart:convert';import 'package:flutter/services.dart';import '../models/class_info.dart';

Future<String> _loadClassInfoJson() async {return await rootBundle.loadString('assets/class_info.json');}

Future<ClassInfo> decodeClassInfo() async {String classInfoJson = await _loadClassInfoJson();

Map<String, dynamic> jsonMap = json.decode(classInfoJson);

ClassInfo classInfo = ClassInfo.fromJson(jsonMap);classInfo.studentList.forEach((student) => print('student name is ${student.name}'));return classInfo;}

上述代码在运行后还是会报错：

Unhandled Exception: type 'List<dynamic>' is not a subtype of type 'List<Student>'

同样，还是在 studentList: json['students'] 出问题了，我们把 json['students'] 的输出来看看：

[{name: 叶湘伦, sex: 男}, {name: 路小雨, sex: 女}]

上述结果的类型为 List<dynamic> 。现在我们需要将 List<dynamic> 转换到一个 List<Student> 类型的数组中，这里需要用到一个操作符 map，map 操作符的作用就是将某种类型转换为另一种类型。如下：

factory ClassInfo.fromJson(Map<String, dynamic> json) {

final originList = json['students'] as List;

List<Student> studentList =

originList.map((value) => Student.fromJson(value)).toList();

return ClassInfo(

id: json['id'], name: json['class_name'], studentList: studentList);

}

输出：

flutter: student name is 叶湘伦 flutter: student name is 路小雨

单纯的数组

member.json

[{"id": 1,"name": "Jack"},{"id": 2,"name": "Rose"},{"id": 3,"name": "Karl"}]

实体：

class MemberList {

List<Member> memberList;

MemberList({this.memberList});

factory MemberList.fromJson(List<dynamic> listJson) {

List<Member> memberList =

listJson.map((value) => Member.fromJson(value)).toList();

return MemberList(memberList: memberList);

}

}

class Member {

int id;

String name;

Member({this.id, this.name});

factory Member.fromJson(Map<String, dynamic> json) {

return Member(id: json['id'], name: json['name']);

}

}

因为 member.json 是一个单纯的数组，所以上述代码中我们创建了一个 MemberList 类来将这个 Member 数组包含起来。

注意下上述代码中 MemberList.fromJson(...) 中的写法。

service:

import 'dart:async';import 'package:flutter/services.dart';import 'dart:convert';import '../models/member.dart';

Future<String> _loadMemberJson() async {return await rootBundle.loadString('assets/member.json');}

Future<MemberList> decodeMemberList() async {String memberListJson = await _loadMemberJson();

List<dynamic> list = json.decode(memberListJson);

MemberList memberList = MemberList.fromJson(list);

memberList.memberList.forEach((member) => print('member name is ${member.name}'));

return memberList;}

输出：

flutter: member name is Jackflutter: member name is Roseflutter: member name is Karl

复杂的 Json 解析

之前的文章 Flutter 中 ListView 的使用 中用到了 豆瓣API ，这个 API 中返回的数据包含了当前热播的电影，大家尝试着按需解析一下吧 ！！！