Parsing a List of Objects in Flutter error - json

Question

I am using code generation to help with working with JSON files. I am wanting to parse a list of objects, but I keep getting the error:
[ERROR:flutter/lib/ui/ui_dart_state.cc(157)] Unhandled Exception: type 'List<dynamic>' is not a subtype of type 'Map<String, dynamic>'
The Json file I want to deserialize (I've already created models files for the json):
[
{
"id": "Nebula",
"setCount": "5 - 3",
"characters": {
"char1": "mario",
"char2": "peach"
},
"notes": "this player has really cool combos and float cancel nairs are cool"
},
{
"id": "Kambo",
"setCount": "2 - 8",
"characters": {
"char1": "fox",
"char2": ""
},
"notes": "I play fox for fun lmao"
},
{
"id": "Quiet",
"setCount": "8 - 3",
"characters": {
"char1": "zero_suit_samus",
"char2": "wolf"
},
"notes": "this player has really cool combos and float cancel nairs are cool"
}
]
I am not sure what I am doing wrong. Here is the where I call to receive a Playlist from the Json:
void setupHomePage() async {
PlayerList playerList = await getPlayerList();
Navigator.pushReplacement(
context,
MaterialPageRoute(
builder: (context) => Home(),
settings: RouteSettings(
arguments: playerList,
),
),
);
}
Decoding the JSON:
PlayerList playerList;
Future<String> _loadPlayerListAsset () async {
return await rootBundle.loadString('assets/nebula.json');
}
Future loadPlayerList () async {
String jsonString = await _loadPlayerListAsset();
final jsonResponse = jsonDecode(jsonString);
playerList = PlayerList.fromJson(jsonResponse);
}
Future<PlayerList> getPlayerList() async {
await loadPlayerList();
print(playerList.toString());
return playerList;
}
Generated JSON code:
#JsonSerializable(explicitToJson: true)
class PlayerList {
PlayerList (
this.players
);
List<Player> players;
factory PlayerList.fromJson (Map<String, dynamic> json) => _$PlayerListFromJson(json);
Map<String, dynamic> toJson() => _$PlayerListToJson(this);
}
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(),
};

Answer 1

The type of jsonResponse here:
final jsonResponse = jsonDecode(jsonString);
Is List since your JSON defines a list of maps.
But then you are doing:
playerList = PlayerList.fromJson(jsonResponse);
...
factory PlayerList.fromJson (Map<String, dynamic> json) => _$PlayerListFromJson(json);
The signature of your fromJson are saying it takes a Map<String, dynamic> which are not compatible with List.
The next problem will be json['players'] which are not going to work since your JSON does not contain any key with the name players. Also, your JSON are a List so it makes no sense.
Example on how to parse the provided JSON
I have make the following code which can parse the JSON you have provided as example:
import 'dart:convert';
class Player {
String id;
String setCount;
Map<String, String> characters;
String notes;
Player.fromJson(Map<String, dynamic> json)
: id = json['id'] as String,
setCount = json['setCount'] as String,
characters = (json['characters'] as Map).cast<String, String>(),
notes = json['notes'] as String;
static List<Player> getPlayersFromJson(List<dynamic> json) =>
json.cast<Map<String, dynamic>>().map((j) => Player.fromJson(j)).toList();
Map<String, dynamic> toJson() => <String, dynamic>{
'id': id,
'setCount': setCount,
'characters': characters,
'notes': notes
};
}
void main() {
const jsonString = '''
[
{
"id": "Nebula",
"setCount": "5 - 3",
"characters": {
"char1": "mario",
"char2": "peach"
},
"notes": "this player has really cool combos and float cancel nairs are cool"
},
{
"id": "Kambo",
"setCount": "2 - 8",
"characters": {
"char1": "fox",
"char2": ""
},
"notes": "I play fox for fun lmao"
},
{
"id": "Quiet",
"setCount": "8 - 3",
"characters": {
"char1": "zero_suit_samus",
"char2": "wolf"
},
"notes": "this player has really cool combos and float cancel nairs are cool"
}
]
''';
final playerList = Player.getPlayersFromJson(json.decode(jsonString) as List);
playerList.forEach((player) => print('${player.id} | ${player.notes}'));
// Nebula | this player has really cool combos and float cancel nairs are cool
// Kambo | I play fox for fun lmao
// Quiet | this player has really cool combos and float cancel nairs are cool
print(json.encode(playerList));
}