Flutter store List of custom Classes in Shared Preferences - json

Question

I have List of custom objects which also have fields with non-primitive datatypes. I would like to store a list of these objects in SharedPreferences. This is my List and also the simple Data:
#JsonSerializable()
class MedicamentsBase {
final List<Medicament> data;
const MedicamentsBase({
required this.data,
});
factory MedicamentsBase.fromJson(Map<String, dynamic> json) =>
_$MedicamentsBaseFromJson(json);
Map<String, dynamic> toJson() => _$MedicamentsBaseToJson(this);
}
#JsonSerializable()
class Medicament {
#JsonKey(name: '_id')
String id;
String name;
int dosageAmount;
String dosageType;
DateTime startDate;
DateTime endDate;
List<DateTime> timesOfDay;
String intakeContext;
bool notify;
int notificationId;
Medicament({
required this.name,
required this.dosageAmount,
required this.dosageType,
required this.startDate,
required this.endDate,
required this.timesOfDay,
required this.intakeContext,
required this.notify,
required this.notificationId,
required this.id,
});
factory Medicament.fromJson(Map<String, dynamic> json) =>
_$MedicamentFromJson(json);
Map<String, dynamic> toJson() => _$MedicamentToJson(this);
}
I already serialized them. But if I try to store the MedicamentsBase like this:
static Future<void> setMedicaments(List<Medicament> medicaments) async {
final SharedPreferences _sharedPreferences =
await SharedPreferences.getInstance();
await _sharedPreferences.setStringList(
'key',
medicaments.map((medicament) => json.encode(medicament)).toList(),
);
}
Things are not working as expected if trying to get the List back like this:
static Future<List<Medicament>> getMedicaments() async {
final SharedPreferences _sharedPreferences =
await SharedPreferences.getInstance();
return MedicamentsBase.fromJson(
_sharedPreferences.getStringList('key') as Map<String, dynamic>,
).data;
}
I think it is because Medicament also has Strings and DateTimes in it. What is the correct way to store and get this kind of data in Shared Preferences?

Answer 1

Shared preferences might not be the way to go if you are intending on saving more complex data types, I think your options are:
Checking out on how to use the hive package
Trying to save primitive type which you can later use to reconstruct your complex data types with using shared preferences
Create a ToJson / FromJson functions in your complex data types, and use the file.dart function which are available as part of flutter to save this data as a json file, take alook at those functions which should be useful to do so:
write the file:
Directory applicationDocumentDirectory =
await getApplicationDocumentsDirectory();
File file = Directory applicationDocumentDirectory =
await getApplicationDocumentsDirectory();
Map<String, dynamic> fileJson = yourDataType.toJson();
String dataAsJsonString = jsonEncode(fileJson);
songDataFile.writeAsStringSync(dataAsJsonString);
String fileData = file.readAsStringSync();
return jsonDecode(fileData);
read the file:
Directory applicationDocumentDirectory =
await getApplicationDocumentsDirectory();
File file = Directory applicationDocumentDirectory =
await getApplicationDocumentsDirectory();
String fileData = file.readAsStringSync();
return jsonDecode(fileData);
Hopefully those ideas help :)