Json

Map<String, dynamic> headerJson = json.decode(jsonstring);  
Header h = Header.fromJson(headerJson);



class Header {

String url;

String from;

String to;

  

Header({required this.url, this.from = '', this.to = ''});

  

Map<String, dynamic> toJson() => {'url': url, 'from': from, 'to': to};

  

String toJsonString() => {'url': url, 'from': from, 'to': to}.toString();

  

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

return Header(

url: json['Url'],

from: json['From'],

to: json['To'],

);

}

}

import 'package:flutter/material.dart';

class User {
  final String name;
  final String email;

  User(this.name, this.email);

  User.fromJson(Map<String, dynamic> json)
      : name = json['name'],
        email = json['email'];

  Map<String, dynamic> toJson() => {
        'name': name,
        'email': email,
      };
}



解码逻辑的责任现在转移到了模型内部。通过这个新方法，你可以很容易地解码获得一个 user 实例。

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Map userMap = jsonDecode(jsonString);
var user = User.fromJson(userMap);

print('Howdy, ${user.name}!');
print('We sent the verification link to ${user.email}.');
要对 user 实例进行编码，将 User 对象传到 jsonEncode() 函数中。你不需要调用 toJson() 方法，因为 jsonEncode() 已经帮你做了这件事。

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String json = jsonEncode(user);