Local JSON deserialization in Flutter using Json_Serializable - json

Question

I'm trying to access a local JSON file in my flutter app but am stuck on how to:
1) Load the json file into my project
2) Parse/decode it using the serialization module I've put together.
The code for the serialisation module Classes:
import 'package:json_annotation/json_annotation.dart';
part 'testJson.g.dart';
#JsonSerializable()
class BaseResponse extends Object with _$BaseResponseSerializerMixin {
final List<Topics> topic;
BaseResponse(
this.topic
);
factory BaseResponse.fromJson(Map<String, dynamic> json) => _$BaseResponseFromJson(json);
}
#JsonSerializable()
class Topics extends Object with _$TopicsSerializerMixin {
final int id;
final String name;
final String color;
final List<Reading> reading;
final int tCompletion;
Topics(
this.id,
this.name,
this.color,
this.reading,
this.tCompletion
);
factory Topics.fromJson(Map<String, dynamic> json) => _$TopicsFromJson(json);
}
#JsonSerializable()
class Reading extends Object with _$ReadingSerializerMixin{
final String name;
final int nLos;
final String description;
final String summary;
final List<LOS> los;
final int rCompletion;
Reading(
this.name,
this.nLos,
this.description,
this.summary,
this.los,
this.rCompletion,
);
factory Reading.fromJson(Map<String, dynamic> json) => _$ReadingFromJson(json);
}
#JsonSerializable()
class LOS extends Object with _$LOSSerializerMixin{
final int id;
final String objective;
final String description;
final String formulae;
LOS(this.id, this.objective, this.description, this.formulae);
factory LOS.fromJson(Map<String, dynamic> json) => _$LOSFromJson(json);
}
#JsonLiteral('jsondata.json')
Map get glossaryData => _$glossaryDataJsonLiteral;
I have built a Model to interpret the response for the Topic Class
class topicModel {
final String topic;
final String color;
final int completion;
topicModel({
this.topic,
this.color,
this.completion
});
topicModel.fromResponse(Topics response)
: topic = response.name,
color = response.color,
completion = response.tCompletion;
}
I'm trying to use future builder to load the local JSON file, but am struggling to return the data and parse it through the classes / model
Widget build(BuildContext context) {
return FutureBuilder(
future: getData(context: context),
builder: (BuildContext context, AsyncSnapshot<List> jsonData) {
if (!jsonData.hasData) {
return Text('not loaded');
}
return Text('loaded');
},
}
Future<List<topicModel>> getData({BuildContext context}) async {
String data = await DefaultAssetBundle.of(context).loadString("assets/data/jsondata.json");
Map jsonMap = json.decode(data);
var testdata = BaseResponse.fromJson(jsonMap);
return topicModel.fromResponse(testdata) as List;
}