Flutter Dart JSONECODE给我错误未处理异常:将对象转换为可编码对象失败
我在编写代码时出错Flutter Dart JSONECODE给我错误未处理异常:将对象转换为可编码对象失败,flutter,dart,Flutter,Dart,我在编写代码时出错 未处理的异常:将对象转换为可编码对象失败:“字对”的实例 我已经阅读了关于json_注释和json_可序列化的内容,但我不知道它们对我的情况有何帮助。当我无法访问“WordPair”类时,我不知道如何使用它 在代码中,我们使用english_words包获得随机的“字对”。我正在尝试将用户选择的一些喜爱的单词保存到共享首选项中。但我不知道如何使列表可序列化。我对飞镖和飞镖很陌生。请帮忙 import "package:flutter/material.dart"; impor
未处理的异常:将对象转换为可编码对象失败:“字对”的实例
我已经阅读了关于json_注释和json_可序列化的内容,但我不知道它们对我的情况有何帮助。当我无法访问“WordPair”类时,我不知道如何使用它
在代码中,我们使用english_words包获得随机的“字对”。我正在尝试将用户选择的一些喜爱的单词保存到共享首选项中。但我不知道如何使列表可序列化。我对飞镖和飞镖很陌生。请帮忙
import "package:flutter/material.dart";
import "package:english_words/english_words.dart";
import 'package:shared_preferences/shared_preferences.dart';
import 'dart:convert';
class RandomWords extends StatefulWidget {
@override
RandomWordsState createState() => RandomWordsState();
}
class RandomWordsState extends State<RandomWords> {
final _randomWordPairs = <WordPair>[];
final _savedWordPairs = Set<WordPair>();
Future<void> _setSavedWordPairs() async {
List<WordPair> savedWordPairsList = _savedWordPairs.toList();
SharedPreferences prefs = await SharedPreferences.getInstance();
await prefs.setString("wordpairs", jsonEncode(savedWordPairsList));
print(prefs.getString("wordpairs"));
}
Future<void> _getSavedWordPairs() async {
SharedPreferences prefs = await SharedPreferences.getInstance();
String savedWordPairsString =
prefs.getString("wordpairs") ?? jsonEncode(<WordPair>[]);
List<WordPair> savedWordPairsList = jsonDecode(savedWordPairsString);
print(savedWordPairsList);
setState(() {
_randomWordPairs.addAll(savedWordPairsList);
_savedWordPairs.addAll(savedWordPairsList);
});
}
Widget _buildList() {
return ListView.builder(
padding: const EdgeInsets.all(16.0),
itemBuilder: (context, item) {
if (item.isOdd) return Divider();
final index = item ~/ 2;
if (index >= _randomWordPairs.length) {
_randomWordPairs.addAll(generateWordPairs().take(10));
}
return _buildRow(_randomWordPairs[index]);
},
);
}
Widget _buildRow(WordPair pair) {
final alreadySaved = _savedWordPairs.contains(pair);
return ListTile(
title: Text(pair.asPascalCase, style: TextStyle(fontSize: 18.0)),
trailing: Icon(
alreadySaved ? Icons.favorite : Icons.favorite_border,
color: alreadySaved ? Colors.red : null,
),
onTap: () {
setState(() {
if (alreadySaved) {
_savedWordPairs.remove(pair);
} else {
_savedWordPairs.add(pair);
}
});
_setSavedWordPairs();
},
);
}
void _pushSaved() {
Navigator.of(context)
.push(MaterialPageRoute(builder: (BuildContext context) {
final Iterable<ListTile> tiles = _savedWordPairs.map((WordPair pair) {
return ListTile(
title: Text(pair.asPascalCase, style: TextStyle(fontSize: 16.0)));
});
final List<Widget> divided =
ListTile.divideTiles(context: context, tiles: tiles).toList();
return Scaffold(
appBar: AppBar(
title: Text("Saved WordPairs"),
),
body: ListView(
children: divided,
),
);
}));
}
@override
void initState() {
super.initState();
_getSavedWordPairs();
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("WordPair Generator"),
actions: <Widget>[
IconButton(
icon: Icon(Icons.list),
onPressed: _pushSaved,
)
],
),
body: _buildList());
}
}
导入“包装:颤振/材料.省道”;
导入“包:英语单词/英语单词.dart”;
导入“package:shared_preferences/shared_preferences.dart”;
导入“dart:convert”;
类RandomWords扩展了StatefulWidget{
@凌驾
RandomWordsState createState()=>RandomWordsState();
}
类RandomWordsState扩展状态{
最终_randomWordPairs=[];
final _savedWordPairs=Set();
Future _setSavedWordPairs()异步{
List savedWordPairsList=_savedWordPairs.toList();
SharedReferences prefs=等待SharedReferences.getInstance();
wait prefs.setString(“字对”,JSONECODE(savedWordPairsList));
打印(prefs.getString(“字对”);
}
Future\u getSavedWordPairs()异步{
SharedReferences prefs=等待SharedReferences.getInstance();
字符串savedWordPairsString=
prefs.getString(“字对”)??JSONECODE([]);
List savedWordPairsList=jsonDecode(savedWordPairsString);
打印(保存或配对列表);
设置状态(){
_addAll(savedWordPairsList);
_savedWordPairs.addAll(savedWordPairsList);
});
}
小部件_buildList(){
返回ListView.builder(
填充:常数边集全部(16.0),
itemBuilder:(上下文,项){
if(item.isOdd)返回分隔符();
最终索引=项目~/2;
如果(索引>=\u randomWordPairs.length){
_addAll(generateWordPairs().take(10));
}
返回_buildRow(_randomWordPairs[index]);
},
);
}
小部件构建行(字对){
final alreadySaved=\u savedWordPairs.contains(pair);
返回列表块(
标题:Text(pair.asPascalCase,style:TextStyle(fontSize:18.0)),
尾随:图标(
alreadySaved?Icons.favorite:Icons.favorite_边框,
颜色:已保存?颜色。红色:空,
),
onTap:(){
设置状态(){
如果(已保存){
_savedWordPairs.remove(对);
}否则{
_savedWordPairs.add(pair);
}
});
_setSavedWordPairs();
},
);
}
作废(){
导航器(上下文)
.push(MaterialPage路由(生成器:(构建上下文){
final Iterable tiles=\u savedWordPairs.map((字对){
返回列表块(
标题:Text(pair.asPascalCase,style:TextStyle(fontSize:16.0));
});
最后的名单有分歧=
divideTiles(上下文:context,tiles:tiles.toList();
返回脚手架(
appBar:appBar(
标题:文本(“保存的字对”),
),
正文:ListView(
儿童:分裂,
),
);
}));
}
@凌驾
void initState(){
super.initState();
_getSavedWordPairs();
}
@凌驾
小部件构建(构建上下文){
返回脚手架(
appBar:appBar(
标题:文本(“字对生成器”),
行动:[
图标按钮(
图标:图标(Icons.list),
按下按钮:\u已保存,
)
],
),
正文:_buildList());
}
}
您可以复制粘贴运行下面的完整代码
您需要扩展
WordPair
并添加toJson()
,fromJson()
代码片段
List<WordPairExt> wordPairExtFromJson(String str) =>
List<WordPairExt>.from(json.decode(str).map((x) => WordPairExt.fromJson(x)));
String wordPairExtToJson(List<WordPairExt> data) => json.encode(List<dynamic>.from(data.map((x) => x.toJson())));
class WordPairExt extends WordPair {
String first;
String second;
WordPairExt({
this.first,
this.second,
}) : super(first, second);
factory WordPairExt.fromJson(Map<String, dynamic> json) => WordPairExt(
first: json["first"],
second: json["second"],
);
Map<String, dynamic> toJson() => {
"first": first,
"second": second,
};
}
List wordPairExtFromJson(字符串str)=>
from(json.decode(str.map)((x)=>WordPairExt.fromJson(x));
字符串wordpairextotojson(List data)=>json.encode(List.from(data.map((x)=>x.toJson()));
类WordPairExt扩展了WordPair{
先串;
弦秒;
WordPairExt({
这,首先,,
这一秒,
}):超级(第一、第二);
工厂WordPairExt.fromJson(映射json)=>WordPairExt(
first:json[“first”],
第二个:json[“第二个”],
);
映射到JSON()=>{
“第一”:第一,
"二":二,,
};
}
工作演示
完整代码
import 'package:flutter/material.dart';
import "package:english_words/english_words.dart";
import 'package:shared_preferences/shared_preferences.dart';
import 'dart:convert';
List<WordPairExt> wordPairExtFromJson(String str) => List<WordPairExt>.from(json.decode(str).map((x) => WordPairExt.fromJson(x)));
String wordPairExtToJson(List<WordPairExt> data) => json.encode(List<dynamic>.from(data.map((x) => x.toJson())));
class WordPairExt extends WordPair {
String first;
String second;
WordPairExt({
this.first,
this.second,
}) : super(first, second);
factory WordPairExt.fromJson(Map<String, dynamic> json) => WordPairExt(
first: json["first"],
second: json["second"],
);
Map<String, dynamic> toJson() => {
"first": first,
"second": second,
};
}
class RandomWords extends StatefulWidget {
@override
RandomWordsState createState() => RandomWordsState();
}
class RandomWordsState extends State<RandomWords> {
final _randomWordPairs = <WordPairExt>[];
final _savedWordPairs = Set<WordPairExt>();
Future<void> _setSavedWordPairs() async {
List<WordPairExt> savedWordPairsList = _savedWordPairs.toList();
SharedPreferences prefs = await SharedPreferences.getInstance();
await prefs.setString("wordpairs", wordPairExtToJson(savedWordPairsList));
print(prefs.getString("wordpairs"));
}
Future<void> _getSavedWordPairs() async {
SharedPreferences prefs = await SharedPreferences.getInstance();
String savedWordPairsString = prefs.getString("wordpairs");
if (savedWordPairsString != null ) {
List<WordPairExt> savedWordPairsList = wordPairExtFromJson(
savedWordPairsString);
print(savedWordPairsList);
setState(() {
_randomWordPairs.addAll(savedWordPairsList);
_savedWordPairs.addAll(savedWordPairsList);
});
}
}
Widget _buildList() {
return ListView.builder(
padding: const EdgeInsets.all(16.0),
itemBuilder: (context, item) {
if (item.isOdd) return Divider();
final index = item ~/ 2;
if (index >= _randomWordPairs.length) {
generateWordPairs().take(10).forEach((wp) {
_randomWordPairs
.add(WordPairExt(first: wp.first, second: wp.second));
});
//_randomWordPairs.addAll(generateWordPairs().take(10).cast());
}
return _buildRow(_randomWordPairs[index]);
},
);
}
Widget _buildRow(WordPair pair) {
final alreadySaved = _savedWordPairs.contains(pair);
return ListTile(
title: Text(pair.asPascalCase, style: TextStyle(fontSize: 18.0)),
trailing: Icon(
alreadySaved ? Icons.favorite : Icons.favorite_border,
color: alreadySaved ? Colors.red : null,
),
onTap: () {
setState(() {
if (alreadySaved) {
_savedWordPairs.remove(pair);
} else {
_savedWordPairs.add(pair);
}
});
_setSavedWordPairs();
},
);
}
void _pushSaved() {
Navigator.of(context)
.push(MaterialPageRoute(builder: (BuildContext context) {
final Iterable<ListTile> tiles = _savedWordPairs.map((WordPair pair) {
return ListTile(
title: Text(pair.asPascalCase, style: TextStyle(fontSize: 16.0)));
});
final List<Widget> divided =
ListTile.divideTiles(context: context, tiles: tiles).toList();
return Scaffold(
appBar: AppBar(
title: Text("Saved WordPairs"),
),
body: ListView(
children: divided,
),
);
}));
}
@override
void initState() {
super.initState();
_getSavedWordPairs();
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("WordPair Generator"),
actions: <Widget>[
IconButton(
icon: Icon(Icons.list),
onPressed: _pushSaved,
)
],
),
body: _buildList());
}
}
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: RandomWords(),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
void _incrementCounter() {
setState(() {
_counter++;
});
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
Text(
'$_counter',
style: Theme.of(context).textTheme.display1,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
),
);
}
}
导入“包装:颤振/材料.省道”;
导入“包:英语单词/英语单词.dart”;
导入“package:shared_preferences/shared_preferences.dart”;
导入“dart:convert”;
List wordPairExtFromJson(String str)=>List.from(json.decode(str.map)(x)=>wordPairExtFromJson(x));
字符串wordpairextotojson(List data)=>json.encode(List.from(data.map((x)=>x.toJson()));
类WordPairExt扩展了WordPair{
先串;
弦秒;
WordPairExt({
这,首先,,
这一秒,
}):超级(第一、第二);
工厂WordPairExt.fromJson(映射json)=>WordPairExt(
first:json[“first”],
第二个:json[“第二个”],
);
映射到JSON()=>{
“第一”:第一,
"二":二,,
};
}
类RandomWords扩展了StatefulWidget{
@凌驾
RandomWordsState createState()=>RandomWordsState();
}
类RandomWordsState扩展状态{
最终_randomWordPairs=[];
final _savedWordPairs=Set();
Future _setSavedWordPairs()异步{
List savedWordPairsList=_savedWordPairs.toList();
SharedReferences prefs=等待SharedReferences.getInstance();
等待prefs.setString(“字对”,wordPairExtToJson(savedWordPairsList));
打印(prefs.getString(“字对”);
}
Future\u getSavedWordPairs()异步{
SharedReferences prefs=等待SharedReferences.getInstance();
字符串savedWordPairsString=