json - 在 Flutter 中本地写入和读取 JSON 文件不包括引号

Question

我正在本地将对象写入 JSON 文件。当我尝试阅读它时，我收到此错误:

E/flutter ( 7621): [ERROR:flutter/lib/ui/ui_dart_state.cc(157)] Unhandled Exception: FormatException: Unexpected character (at character 2)
E/flutter ( 7621): {players: [{id: Nebula, setCount: 0 - 0, characters: {char1: ice_climbers, char2: captain_falcon}, notes: }]}
E/flutter ( 7621):  ^

我知道我收到此错误的原因是 player 不在引号之间。即“玩家”。我不知道如何将对象写成包含引号的 JSON。

此代码由 JsonSerializableGenerator 生成
PlayerList.toJson:

PlayerList _$PlayerListFromJson(Map<String, dynamic> json) {
  return PlayerList(
    (json['players'] as List)
        ?.map((e) =>
            e == null ? null : Player.fromJson(e as Map<String, dynamic>))
        ?.toList(),
  );
}

Map<String, dynamic> _$PlayerListToJson(PlayerList instance) =>
    <String, dynamic>{
      'players': instance.players?.map((e) => e?.toJson())?.toList(),
    };

这是我读写文件的方式:

Future<String> get _localPath async {
  final directory = await getApplicationDocumentsDirectory();
  return directory.path;
}

Future<File> get _localFile async {
  final path = await _localPath;
  return File('$path/playerData.json');
}

Future<File> writePlayerData(PlayerList playerList) async {
  final file = await _localFile;
  return file.writeAsString(playerList.toJson().toString());
}

Future<PlayerList> readPlayerData () async {
  try {
    final file = await _localFile;
    String contents = await file.readAsString();
    final jsonResponse = jsonDecode(contents);
    PlayerList playerList = PlayerList.fromJson(jsonResponse);
    return playerList;
  } catch (e) {
    print(e);
    return getPlayerList(); //just loads a placeholder json in the assets folder;
  }
}

我希望将 JSON 格式化为:

{
  "players": [
    {
      "id": "Filler Character",
      "setCount": "0 - 0",
      "characters": {
        "char1": "",
        "char2": ""
      },
      "notes": "Filler Character"
    }
  ]
}

程序保存的内容:

{players: [{id: Nebula, setCount: 0 - 0, characters: {char1: ice_climbers, char2: captain_falcon}, notes: }]}

我是否需要手动将引号添加回 JSON，或者是否有不同的保存方式？

Answer 1

让，test.json 是您桌面上本地存储的 json 文件。 test.json -

[
  {"name":"Ash","age":"22","hobby":"golf"},
  {"name":"philip","age":"17","hobby":"fishing"},
  {"name":"charles","age":"32","hobby":"drawing"},
]

现在我们要从中读取并写入它。下面的代码完成了任务。 test.dart -

import 'dart:io';
import 'dart:convert';

List<Player> players = [];

void main() async{
    print("hello world");
    final File file = File('D:/Sadi/.../test.json'); //load the json file
    await readPlayerData(file); //read data from json file
    
    Player newPlayer = Player(  //add a new item to data list
      'Samy Brook',
      '31',
      'cooking'
      );

  players.add(newPlayer);

  print(players.length);

  players  //convert list data  to json 
      .map(
        (player) => player.toJson(),
      )
      .toList();
      
    file.writeAsStringSync(json.encode(players));  //write (the whole list) to json file
}

Future<void> readPlayerData (File file) async { 
  
    
    String contents = await file.readAsString();
    var jsonResponse = jsonDecode(contents);
    
    for(var p in jsonResponse){
        
        Player player = Player(p['name'],p['age'],p['hobby']);
        players.add(player);
    }
    
      
}

class Player {
  late String name;
  late String age;
  late String hobby;
  

  Player(
     this.name,
     this.age,
    this.hobby,
  
  );

  Player.fromJson(Map<String, dynamic> json) {
    name = json['name'];
    age = json['age'];
    hobby = json['hobby'];
    
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['name'] = this.name;
    data['age'] = this.age;
    data['hobby'] = this.hobby;
    
    return data;
  }
  
}