Dart 对象 -> JSON 字符串无法转换为 JSON
Dart Object -> JSON String failing to convert to JSON
我正在尝试将对象序列化为 JSON，然后从 JSON 返回到对象。
这是应该给我正确的代码片段 JSON:
LoginRequest req = new LoginRequest();
req.username = username;
req.password = password;
req.created = 123456;
req.test = "KOTS";
print(req.toString());
我在控制台中看到的是这样的：
{} (:1)
在 pubspec.yaml 中，我正在导入 json_object 作为依赖项：
environment:
sdk: '>=1.0.0 <2.0.0'
dependencies:
...
json_object: any
我有一个扩展 JsonObject 的基本消息 class：
import 'package:json_object/json_object.dart';
class Message extends JsonObject {
int created = new DateTime.now().millisecondsSinceEpoch;
}
然后我有一个扩展消息的登录请求：
import 'Message.dart';
class LoginRequest extends Message {
String _username;
String _password;
String test;
String get username => _username;
set username(String username) {
_username = username.trim();
}
String get password => _password;
set password(String password) {
_password = password.trim();
}
}
我以为只有baseclass会转Json，所以又写了一个测试用例：
Message msg = new Message();
msg.created = 123456;
print(msg.toString());
这也是打印：
{} (:1)
调用 objectToJson 做同样的事情：
objectToJson(msg).then((jsonStr) => print(jsonStr));
objectToJson(req).then((jsonStr) => print(jsonStr));
输出：
{}
{}
删除 extends JsonObject 会导致上面的代码产生堆栈跟踪：
Exception: Uncaught Error: Converting object to an encodable object failed.
Stack Trace:
#0 _JsonStringifier.writeObject (dart:convert/json.dart:660)
#1 _JsonStringStringifier.printOn (dart:convert/json.dart:831)
#2 _JsonStringStringifier.stringify (dart:convert/json.dart:813)
#3 JsonEncoder.convert (dart:convert/json.dart:243)
#4 JsonCodec.encode (dart:convert/json.dart:141)
#5 login (package:falm/login-dialog.dart:47:22)
#6 Function.apply (dart:core-patch/function_patch.dart:28)
#7 GeneratedObjectAccessorService.invoke (package:smoke/static.dart:149:28)
#8 invoke (package:smoke/smoke.dart:43:41)
#9 HtmlElement&Polymer.dispatchMethod (package:polymer/src/instance.dart:1054:19)
#10 BindingDelegate&PolymerEventBindings.getEventHandler.<anonymous closure> (package:polymer/src/events.dart:82:32)
#11 _RootZone.runUnaryGuarded (dart:async/zone.dart:1093)
#12 _RootZone.bindUnaryCallback.<anonymous closure> (dart:async/zone.dart:1122)
#13 BindingDelegate&PolymerEventBindings.prepareEventBinding.<anonymous closure>.<anonymous closure> (package:polymer/src/events.dart:101:67)
Clicked Login (:1)
Exception: Uncaught Error: Class '_LocalClassMirror' has no instance getter 'getters'.
NoSuchMethodError: method not found: 'getters'
Receiver: Instance of '_LocalClassMirror'
Arguments: []
Stack Trace:
#0 Object.noSuchMethod (dart:core-patch/object_patch.dart:45)
#1 _serializeObject (package:json_object/src/mirror_based_serializer.dart:127:16)
#2 objectToSerializable (package:json_object/src/mirror_based_serializer.dart:53:21)
#3 objectToJson (package:json_object/src/mirror_based_serializer.dart:22:23)
#4 login (package:falm/login-dialog.dart:43:17)
#5 Function.apply (dart:core-patch/function_patch.dart:28)
#6 GeneratedObjectAccessorService.invoke (package:smoke/static.dart:149:28)
#7 invoke (package:smoke/smoke.dart:43:41)
#8 HtmlElement&Polymer.dispatchMethod (package:polymer/src/instance.dart:1054:19)
#9 BindingDelegate&PolymerEventBindings.getEventHandler.<anonymous closure> (package:polymer/src/events.dart:82:32)
#10 _RootZone.runUnaryGuarded (dart:async/zone.dart:1093)
#11 _RootZone.bindUnaryCallback.<anonymous closure> (dart:async/zone.dart:1122)
#12 BindingDelegate&PolymerEventBindings.prepareEventBinding.<anonymous closure>.<anonymous closure> (package:polymer/src/events.dart:101:67)
Clicked Login (:1)
Exception: Uncaught Error: Converting object to an encodable object failed.
Stack Trace:
#0 _JsonStringifier.writeObject (dart:convert/json.dart:660)
#1 _JsonStringStringifier.printOn (dart:convert/json.dart:831)
#2 _JsonStringStringifier.stringify (dart:convert/json.dart:813)
#3 JsonEncoder.convert (dart:convert/json.dart:243)
#4 JsonCodec.encode (dart:convert/json.dart:141)
#5 login (package:falm/login-dialog.dart:47:22)
#6 Function.apply (dart:core-patch/function_patch.dart:28)
#7 GeneratedObjectAccessorService.invoke (package:smoke/static.dart:149:28)
#8 invoke (package:smoke/smoke.dart:43:41)
#9 HtmlElement&Polymer.dispatchMethod (package:polymer/src/instance.dart:1054:19)
#10 BindingDelegate&PolymerEventBindings.getEventHandler.<anonymous closure> (package:polymer/src/events.dart:82:32)
#11 _RootZone.runUnaryGuarded (dart:async/zone.dart:1093)
#12 _RootZone.bindUnaryCallback.<anonymous closure> (dart:async/zone.dart:1122)
#13 BindingDelegate&PolymerEventBindings.prepareEventBinding.<anonymous closure>.<anonymous closure> (package:polymer/src/events.dart:101:67)
Clicked Login (:1)
Exception: Uncaught Error: Class '_LocalClassMirror' has no instance getter 'getters'.
NoSuchMethodError: method not found: 'getters'
Receiver: Instance of '_LocalClassMirror'
Arguments: []
Stack Trace:
#0 Object.noSuchMethod (dart:core-patch/object_patch.dart:45)
#1 _serializeObject (package:json_object/src/mirror_based_serializer.dart:127:16)
#2 objectToSerializable (package:json_object/src/mirror_based_serializer.dart:53:21)
#3 objectToJson (package:json_object/src/mirror_based_serializer.dart:22:23)
#4 login (package:falm/login-dialog.dart:44:17)
#5 Function.apply (dart:core-patch/function_patch.dart:28)
#6 GeneratedObjectAccessorService.invoke (package:smoke/static.dart:149:28)
#7 invoke (package:smoke/smoke.dart:43:41)
#8 HtmlElement&Polymer.dispatchMethod (package:polymer/src/instance.dart:1054:19)
#9 BindingDelegate&PolymerEventBindings.getEventHandler.<anonymous closure> (package:polymer/src/events.dart:82:32)
#10 _RootZone.runUnaryGuarded (dart:async/zone.dart:1093)
#11 _RootZone.bindUnaryCallback.<anonymous closure> (dart:async/zone.dart:1122)
#12 BindingDelegate&PolymerEventBindings.prepareEventBinding.<anonymous closure>.<anonymous closure> (package:polymer/src/events.dart:101:67)
导入 dart:convert 并使用 JSON.encode 做同样的事情：
import 'dart:convert' show JSON;
...
print(JSON.encode(msg));
print(JSON.encode(req));
输出：
{}
{}
如果我删除扩展 JsonObject，它会抛出一个堆栈跟踪：
Exception: Uncaught Error: Converting object to an encodable object failed.
Stack Trace:
#0 _JsonStringifier.writeObject (dart:convert/json.dart:660)
#1 _JsonStringStringifier.printOn (dart:convert/json.dart:831)
#2 _JsonStringStringifier.stringify (dart:convert/json.dart:813)
#3 JsonEncoder.convert (dart:convert/json.dart:243)
#4 JsonCodec.encode (dart:convert/json.dart:141)
#5 login (package:falm/login-dialog.dart:47:22)
#6 Function.apply (dart:core-patch/function_patch.dart:28)
#7 GeneratedObjectAccessorService.invoke (package:smoke/static.dart:149:28)
#8 invoke (package:smoke/smoke.dart:43:41)
#9 HtmlElement&Polymer.dispatchMethod (package:polymer/src/instance.dart:1054:19)
#10 BindingDelegate&PolymerEventBindings.getEventHandler.<anonymous closure> (package:polymer/src/events.dart:82:32)
#11 _RootZone.runUnaryGuarded (dart:async/zone.dart:1093)
#12 _RootZone.bindUnaryCallback.<anonymous closure> (dart:async/zone.dart:1122)
#13 BindingDelegate&PolymerEventBindings.prepareEventBinding.<anonymous closure>.<anonymous closure> (package:polymer/src/events.dart:101:67)
Clicked Login (:1)
Exception: Uncaught Error: Class '_LocalClassMirror' has no instance getter 'getters'.
NoSuchMethodError: method not found: 'getters'
Receiver: Instance of '_LocalClassMirror'
Arguments: []
Stack Trace:
#0 Object.noSuchMethod (dart:core-patch/object_patch.dart:45)
#1 _serializeObject (package:json_object/src/mirror_based_serializer.dart:127:16)
#2 objectToSerializable (package:json_object/src/mirror_based_serializer.dart:53:21)
#3 objectToJson (package:json_object/src/mirror_based_serializer.dart:22:23)
#4 login (package:falm/login-dialog.dart:43:17)
#5 Function.apply (dart:core-patch/function_patch.dart:28)
#6 GeneratedObjectAccessorService.invoke (package:smoke/static.dart:149:28)
#7 invoke (package:smoke/smoke.dart:43:41)
#8 HtmlElement&Polymer.dispatchMethod (package:polymer/src/instance.dart:1054:19)
#9 BindingDelegate&PolymerEventBindings.getEventHandler.<anonymous closure> (package:polymer/src/events.dart:82:32)
#10 _RootZone.runUnaryGuarded (dart:async/zone.dart:1093)
#11 _RootZone.bindUnaryCallback.<anonymous closure> (dart:async/zone.dart:1122)
#12 BindingDelegate&PolymerEventBindings.prepareEventBinding.<anonymous closure>.<anonymous closure> (package:polymer/src/events.dart:101:67)
Clicked Login (:1)
Exception: Uncaught Error: Converting object to an encodable object failed.
Stack Trace:
#0 _JsonStringifier.writeObject (dart:convert/json.dart:660)
#1 _JsonStringStringifier.printOn (dart:convert/json.dart:831)
#2 _JsonStringStringifier.stringify (dart:convert/json.dart:813)
#3 JsonEncoder.convert (dart:convert/json.dart:243)
#4 JsonCodec.encode (dart:convert/json.dart:141)
#5 login (package:falm/login-dialog.dart:47:22)
#6 Function.apply (dart:core-patch/function_patch.dart:28)
#7 GeneratedObjectAccessorService.invoke (package:smoke/static.dart:149:28)
#8 invoke (package:smoke/smoke.dart:43:41)
#9 HtmlElement&Polymer.dispatchMethod (package:polymer/src/instance.dart:1054:19)
#10 BindingDelegate&PolymerEventBindings.getEventHandler.<anonymous closure> (package:polymer/src/events.dart:82:32)
#11 _RootZone.runUnaryGuarded (dart:async/zone.dart:1093)
#12 _RootZone.bindUnaryCallback.<anonymous closure> (dart:async/zone.dart:1122)
#13 BindingDelegate&PolymerEventBindings.prepareEventBinding.<anonymous closure>.<anonymous closure> (package:polymer/src/events.dart:101:67)
JsonObject 仍然是将对象序列化为 JSON 和将对象反序列化为 JSON 的正确方法吗？ （我在代码版权 2013 中看到现在已经很古老了）。如果是这样，我是否在 classes 中遗漏了什么？
在 dart cookbook 中有一些示例，其中每个 class 都有自己的 toJson 方法，并且所有值都手动复制到映射中，如果我的整个应用程序是 JSON，这很麻烦-driven，那么我将花费大部分时间编写样板 toJson / fromJson 方法——这正是我想要摆脱的，因此选择 dart 的原因。
此外，我在 Whosebug 上看到使用镜像的示例，然后评论说 dart2js 不完全支持镜像 - 因为这是一个基于浏览器的应用程序，所以它可以编译为 javascript 至关重要.
更新:
根据罗伯特的回答，似乎做样板是不可避免的：
Message.dart
import 'dart:convert' show JSON;
class Message {
int created = new DateTime.now().millisecondsSinceEpoch;
Map toJson() {
Map map = new Map();
map["created"] = this.created;
return map;
}
String toString(){
return JSON.encode(this);
}
}
LoginRequest.dart
import 'Message.dart';
class LoginRequest extends Message {
String _username;
String _password;
String test;
String get username => _username;
set username(String username) {
_username = username.trim();
}
String get password => _password;
set password(String password) {
_password = password.trim();
}
Map toJson() {
Map map = super.toJson();
map["username"] = this.username;
map["password"] = this.password;
return map;
}
}
测试代码：
LoginRequest req = new LoginRequest();
req.username = username;
req.password = password;
req.created = 123456;
req.test = "KOTS";
print(req);
// outputs: {"created":123456,"username":"asdfasdf","password":"adfasdf"} (:1)
Message msg = new Message();
msg.created = 123456;
print(msg);
// outputs: {"created":123456} (:1)
toString 我只需要在 Message class 上实现一次，toJson 将需要在每个 class.
上实现
我认为你的问题是你使用了print(req.toString());。你试过这样做吗：
objectToJson(req).then((jsonStr) => print(jsonStr)); 也许这会给你一个 json 字符串。
我个人觉得您实际上应该提供一个 toJson/toObject 方法，因为您可以完全控制序列化的内容以及序列化的方式（例如排除私有字段、空值...）。
// 编辑
因为你使用 extends JsonObject toString() returns 一个空映射。
// 编辑
https://code.google.com/p/dart/issues/detail?id=6490 看起来好像没有得到很好的支持。但是无论如何你都不能使用 json_object 包。
异常：未捕获错误：Class '_LocalClassMirror' 没有实例 getter 'getters'。这应该是因为该软件包需要实验镜像功能。
使用 JSON.encode 不能将对象放入其中。见 https://api.dartlang.org/apidocs/channels/stable/dartdoc-viewer/dart:convert.JsonCodec#id_encode :
要么指定第二个参数，要么实现 .toJson().
我正在尝试将对象序列化为 JSON，然后从 JSON 返回到对象。
这是应该给我正确的代码片段 JSON:
LoginRequest req = new LoginRequest();
req.username = username;
req.password = password;
req.created = 123456;
req.test = "KOTS";
print(req.toString());
我在控制台中看到的是这样的：
{} (:1)
在 pubspec.yaml 中，我正在导入 json_object 作为依赖项：
environment:
sdk: '>=1.0.0 <2.0.0'
dependencies:
...
json_object: any
我有一个扩展 JsonObject 的基本消息 class：
import 'package:json_object/json_object.dart';
class Message extends JsonObject {
int created = new DateTime.now().millisecondsSinceEpoch;
}
然后我有一个扩展消息的登录请求：
import 'Message.dart';
class LoginRequest extends Message {
String _username;
String _password;
String test;
String get username => _username;
set username(String username) {
_username = username.trim();
}
String get password => _password;
set password(String password) {
_password = password.trim();
}
}
我以为只有baseclass会转Json，所以又写了一个测试用例：
Message msg = new Message();
msg.created = 123456;
print(msg.toString());
这也是打印：
{} (:1)
调用 objectToJson 做同样的事情：
objectToJson(msg).then((jsonStr) => print(jsonStr));
objectToJson(req).then((jsonStr) => print(jsonStr));
输出：
{}
{}
删除 extends JsonObject 会导致上面的代码产生堆栈跟踪：
Exception: Uncaught Error: Converting object to an encodable object failed.
Stack Trace:
#0 _JsonStringifier.writeObject (dart:convert/json.dart:660)
#1 _JsonStringStringifier.printOn (dart:convert/json.dart:831)
#2 _JsonStringStringifier.stringify (dart:convert/json.dart:813)
#3 JsonEncoder.convert (dart:convert/json.dart:243)
#4 JsonCodec.encode (dart:convert/json.dart:141)
#5 login (package:falm/login-dialog.dart:47:22)
#6 Function.apply (dart:core-patch/function_patch.dart:28)
#7 GeneratedObjectAccessorService.invoke (package:smoke/static.dart:149:28)
#8 invoke (package:smoke/smoke.dart:43:41)
#9 HtmlElement&Polymer.dispatchMethod (package:polymer/src/instance.dart:1054:19)
#10 BindingDelegate&PolymerEventBindings.getEventHandler.<anonymous closure> (package:polymer/src/events.dart:82:32)
#11 _RootZone.runUnaryGuarded (dart:async/zone.dart:1093)
#12 _RootZone.bindUnaryCallback.<anonymous closure> (dart:async/zone.dart:1122)
#13 BindingDelegate&PolymerEventBindings.prepareEventBinding.<anonymous closure>.<anonymous closure> (package:polymer/src/events.dart:101:67)
Clicked Login (:1)
Exception: Uncaught Error: Class '_LocalClassMirror' has no instance getter 'getters'.
NoSuchMethodError: method not found: 'getters'
Receiver: Instance of '_LocalClassMirror'
Arguments: []
Stack Trace:
#0 Object.noSuchMethod (dart:core-patch/object_patch.dart:45)
#1 _serializeObject (package:json_object/src/mirror_based_serializer.dart:127:16)
#2 objectToSerializable (package:json_object/src/mirror_based_serializer.dart:53:21)
#3 objectToJson (package:json_object/src/mirror_based_serializer.dart:22:23)
#4 login (package:falm/login-dialog.dart:43:17)
#5 Function.apply (dart:core-patch/function_patch.dart:28)
#6 GeneratedObjectAccessorService.invoke (package:smoke/static.dart:149:28)
#7 invoke (package:smoke/smoke.dart:43:41)
#8 HtmlElement&Polymer.dispatchMethod (package:polymer/src/instance.dart:1054:19)
#9 BindingDelegate&PolymerEventBindings.getEventHandler.<anonymous closure> (package:polymer/src/events.dart:82:32)
#10 _RootZone.runUnaryGuarded (dart:async/zone.dart:1093)
#11 _RootZone.bindUnaryCallback.<anonymous closure> (dart:async/zone.dart:1122)
#12 BindingDelegate&PolymerEventBindings.prepareEventBinding.<anonymous closure>.<anonymous closure> (package:polymer/src/events.dart:101:67)
Clicked Login (:1)
Exception: Uncaught Error: Converting object to an encodable object failed.
Stack Trace:
#0 _JsonStringifier.writeObject (dart:convert/json.dart:660)
#1 _JsonStringStringifier.printOn (dart:convert/json.dart:831)
#2 _JsonStringStringifier.stringify (dart:convert/json.dart:813)
#3 JsonEncoder.convert (dart:convert/json.dart:243)
#4 JsonCodec.encode (dart:convert/json.dart:141)
#5 login (package:falm/login-dialog.dart:47:22)
#6 Function.apply (dart:core-patch/function_patch.dart:28)
#7 GeneratedObjectAccessorService.invoke (package:smoke/static.dart:149:28)
#8 invoke (package:smoke/smoke.dart:43:41)
#9 HtmlElement&Polymer.dispatchMethod (package:polymer/src/instance.dart:1054:19)
#10 BindingDelegate&PolymerEventBindings.getEventHandler.<anonymous closure> (package:polymer/src/events.dart:82:32)
#11 _RootZone.runUnaryGuarded (dart:async/zone.dart:1093)
#12 _RootZone.bindUnaryCallback.<anonymous closure> (dart:async/zone.dart:1122)
#13 BindingDelegate&PolymerEventBindings.prepareEventBinding.<anonymous closure>.<anonymous closure> (package:polymer/src/events.dart:101:67)
Clicked Login (:1)
Exception: Uncaught Error: Class '_LocalClassMirror' has no instance getter 'getters'.
NoSuchMethodError: method not found: 'getters'
Receiver: Instance of '_LocalClassMirror'
Arguments: []
Stack Trace:
#0 Object.noSuchMethod (dart:core-patch/object_patch.dart:45)
#1 _serializeObject (package:json_object/src/mirror_based_serializer.dart:127:16)
#2 objectToSerializable (package:json_object/src/mirror_based_serializer.dart:53:21)
#3 objectToJson (package:json_object/src/mirror_based_serializer.dart:22:23)
#4 login (package:falm/login-dialog.dart:44:17)
#5 Function.apply (dart:core-patch/function_patch.dart:28)
#6 GeneratedObjectAccessorService.invoke (package:smoke/static.dart:149:28)
#7 invoke (package:smoke/smoke.dart:43:41)
#8 HtmlElement&Polymer.dispatchMethod (package:polymer/src/instance.dart:1054:19)
#9 BindingDelegate&PolymerEventBindings.getEventHandler.<anonymous closure> (package:polymer/src/events.dart:82:32)
#10 _RootZone.runUnaryGuarded (dart:async/zone.dart:1093)
#11 _RootZone.bindUnaryCallback.<anonymous closure> (dart:async/zone.dart:1122)
#12 BindingDelegate&PolymerEventBindings.prepareEventBinding.<anonymous closure>.<anonymous closure> (package:polymer/src/events.dart:101:67)
导入 dart:convert 并使用 JSON.encode 做同样的事情：
import 'dart:convert' show JSON;
...
print(JSON.encode(msg));
print(JSON.encode(req));
输出：
{}
{}
如果我删除扩展 JsonObject，它会抛出一个堆栈跟踪：
Exception: Uncaught Error: Converting object to an encodable object failed.
Stack Trace:
#0 _JsonStringifier.writeObject (dart:convert/json.dart:660)
#1 _JsonStringStringifier.printOn (dart:convert/json.dart:831)
#2 _JsonStringStringifier.stringify (dart:convert/json.dart:813)
#3 JsonEncoder.convert (dart:convert/json.dart:243)
#4 JsonCodec.encode (dart:convert/json.dart:141)
#5 login (package:falm/login-dialog.dart:47:22)
#6 Function.apply (dart:core-patch/function_patch.dart:28)
#7 GeneratedObjectAccessorService.invoke (package:smoke/static.dart:149:28)
#8 invoke (package:smoke/smoke.dart:43:41)
#9 HtmlElement&Polymer.dispatchMethod (package:polymer/src/instance.dart:1054:19)
#10 BindingDelegate&PolymerEventBindings.getEventHandler.<anonymous closure> (package:polymer/src/events.dart:82:32)
#11 _RootZone.runUnaryGuarded (dart:async/zone.dart:1093)
#12 _RootZone.bindUnaryCallback.<anonymous closure> (dart:async/zone.dart:1122)
#13 BindingDelegate&PolymerEventBindings.prepareEventBinding.<anonymous closure>.<anonymous closure> (package:polymer/src/events.dart:101:67)
Clicked Login (:1)
Exception: Uncaught Error: Class '_LocalClassMirror' has no instance getter 'getters'.
NoSuchMethodError: method not found: 'getters'
Receiver: Instance of '_LocalClassMirror'
Arguments: []
Stack Trace:
#0 Object.noSuchMethod (dart:core-patch/object_patch.dart:45)
#1 _serializeObject (package:json_object/src/mirror_based_serializer.dart:127:16)
#2 objectToSerializable (package:json_object/src/mirror_based_serializer.dart:53:21)
#3 objectToJson (package:json_object/src/mirror_based_serializer.dart:22:23)
#4 login (package:falm/login-dialog.dart:43:17)
#5 Function.apply (dart:core-patch/function_patch.dart:28)
#6 GeneratedObjectAccessorService.invoke (package:smoke/static.dart:149:28)
#7 invoke (package:smoke/smoke.dart:43:41)
#8 HtmlElement&Polymer.dispatchMethod (package:polymer/src/instance.dart:1054:19)
#9 BindingDelegate&PolymerEventBindings.getEventHandler.<anonymous closure> (package:polymer/src/events.dart:82:32)
#10 _RootZone.runUnaryGuarded (dart:async/zone.dart:1093)
#11 _RootZone.bindUnaryCallback.<anonymous closure> (dart:async/zone.dart:1122)
#12 BindingDelegate&PolymerEventBindings.prepareEventBinding.<anonymous closure>.<anonymous closure> (package:polymer/src/events.dart:101:67)
Clicked Login (:1)
Exception: Uncaught Error: Converting object to an encodable object failed.
Stack Trace:
#0 _JsonStringifier.writeObject (dart:convert/json.dart:660)
#1 _JsonStringStringifier.printOn (dart:convert/json.dart:831)
#2 _JsonStringStringifier.stringify (dart:convert/json.dart:813)
#3 JsonEncoder.convert (dart:convert/json.dart:243)
#4 JsonCodec.encode (dart:convert/json.dart:141)
#5 login (package:falm/login-dialog.dart:47:22)
#6 Function.apply (dart:core-patch/function_patch.dart:28)
#7 GeneratedObjectAccessorService.invoke (package:smoke/static.dart:149:28)
#8 invoke (package:smoke/smoke.dart:43:41)
#9 HtmlElement&Polymer.dispatchMethod (package:polymer/src/instance.dart:1054:19)
#10 BindingDelegate&PolymerEventBindings.getEventHandler.<anonymous closure> (package:polymer/src/events.dart:82:32)
#11 _RootZone.runUnaryGuarded (dart:async/zone.dart:1093)
#12 _RootZone.bindUnaryCallback.<anonymous closure> (dart:async/zone.dart:1122)
#13 BindingDelegate&PolymerEventBindings.prepareEventBinding.<anonymous closure>.<anonymous closure> (package:polymer/src/events.dart:101:67)
JsonObject 仍然是将对象序列化为 JSON 和将对象反序列化为 JSON 的正确方法吗？ （我在代码版权 2013 中看到现在已经很古老了）。如果是这样，我是否在 classes 中遗漏了什么？
在 dart cookbook 中有一些示例，其中每个 class 都有自己的 toJson 方法，并且所有值都手动复制到映射中，如果我的整个应用程序是 JSON，这很麻烦-driven，那么我将花费大部分时间编写样板 toJson / fromJson 方法——这正是我想要摆脱的，因此选择 dart 的原因。
此外，我在 Whosebug 上看到使用镜像的示例，然后评论说 dart2js 不完全支持镜像 - 因为这是一个基于浏览器的应用程序，所以它可以编译为 javascript 至关重要.
更新:
根据罗伯特的回答，似乎做样板是不可避免的：
Message.dart
import 'dart:convert' show JSON;
class Message {
int created = new DateTime.now().millisecondsSinceEpoch;
Map toJson() {
Map map = new Map();
map["created"] = this.created;
return map;
}
String toString(){
return JSON.encode(this);
}
}
LoginRequest.dart
import 'Message.dart';
class LoginRequest extends Message {
String _username;
String _password;
String test;
String get username => _username;
set username(String username) {
_username = username.trim();
}
String get password => _password;
set password(String password) {
_password = password.trim();
}
Map toJson() {
Map map = super.toJson();
map["username"] = this.username;
map["password"] = this.password;
return map;
}
}
测试代码：
LoginRequest req = new LoginRequest();
req.username = username;
req.password = password;
req.created = 123456;
req.test = "KOTS";
print(req);
// outputs: {"created":123456,"username":"asdfasdf","password":"adfasdf"} (:1)
Message msg = new Message();
msg.created = 123456;
print(msg);
// outputs: {"created":123456} (:1)
toString 我只需要在 Message class 上实现一次，toJson 将需要在每个 class.
上实现我认为你的问题是你使用了print(req.toString());。你试过这样做吗：
objectToJson(req).then((jsonStr) => print(jsonStr)); 也许这会给你一个 json 字符串。
我个人觉得您实际上应该提供一个 toJson/toObject 方法，因为您可以完全控制序列化的内容以及序列化的方式（例如排除私有字段、空值...）。
// 编辑
因为你使用 extends JsonObject toString() returns 一个空映射。
// 编辑
https://code.google.com/p/dart/issues/detail?id=6490 看起来好像没有得到很好的支持。但是无论如何你都不能使用 json_object 包。
异常：未捕获错误：Class '_LocalClassMirror' 没有实例 getter 'getters'。这应该是因为该软件包需要实验镜像功能。
使用 JSON.encode 不能将对象放入其中。见 https://api.dartlang.org/apidocs/channels/stable/dartdoc-viewer/dart:convert.JsonCodec#id_encode :
要么指定第二个参数，要么实现 .toJson().