How to deserialize an Object from Map (DART) - json

Question

how can I re-create objects from a serialized/deserialized map of objects?
import 'dart:convert';
class InternalTx {
int a;
bool b;
InternalTx(this.a, this.b);
factory InternalTx.fromJson(Map<String, dynamic> json) =>
InternalTxFromJson(json);
Map<String, dynamic> toJson() => InternalTxToJson(this);
}
InternalTx InternalTxFromJson(Map<String, dynamic> json) => InternalTx(
json['a'] as int,
json['b'] as bool,
);
Map<String, dynamic> InternalTxToJson(InternalTx instance) => <String, dynamic>{
'a': instance.a,
'b': instance.b,
};
main() {
Map<String, InternalTx> m = {};
for (int i=0; i<10; i++)
{
InternalTx itx = InternalTx(i, false);
m["Hello: $i"] = itx;
}
String serM = jsonEncode(m);
print(serM);
////SERILIZED OKAY
Map<String, dynamic> n = jsonDecode(serM);
InternalTx newItx = n["Hello: 0"]; <-- Problem here.
print(newItx);
}
Output:
{"Hello: 0":{"a":0,"b":false},"Hello: 1":{"a":1,"b":false},"Hello: 2":{"a":2,"b":false},"Hello: 3":{"a":3,"b":false},"Hello: 4":{"a":4,"b":false},"Hello: 5":{"a":5,"b":false},"Hello: 6":{"a":6,"b":false},"Hello: 7":{"a":7,"b":false},"Hello: 8":{"a":8,"b":false},"Hello: 9":{"a":9,"b":false}}
Uncaught Error: TypeError: Instance of '_JsonMap': type '_JsonMap' is not a subtype of type 'InternalTx'
What is missing here to deserialize the map of objects correctly?
Thanks!

Answer 1

You need to actually call the InternalTx.fromJson constructor since this is not done automatically. So your last piece of code should be:
////SERILIZED OKAY
Map<String, dynamic> n = jsonDecode(serM);
InternalTx newItx = InternalTx.fromJson(n["Hello: 0"]);
print(newItx); // Instance of 'InternalTx'