Good afternoon, I may have found a small error, but I can't figure it out until now.. I have the following class in dart, the purpose of this class is to receive json and transform each field to object

class Attributes {
  final String lpn; //itemId
  final String type; //itemType (REEL,FEEDER,ETC)
  final String feederContainer; //containerId
  final String feederSide; //locationInContainer(A o B)
  final String locationInTool; //locationInTool

  Attributes(
      {required this.lpn,
      required this.type,
      required this.feederContainer,
      required this.feederSide,
      required this.locationInTool});

  factory Attributes.fromJson(Map json) {
   return Attributes(
     lpn: json['itemId'],
     type: json['itemType'],
      feederContainer: json['containerId'],
      feederSide: json['locationInContainer'],
      locationInTool: json['locationInTool'],
    );
  }
}

class PartNumberAt {
  final String partNumber; //partNumber
  final String quantity; //quantity
  final String initialQuantity; //initialQuantity

  PartNumberAt(
      {required this.partNumber,
      required this.quantity,
      required this.initialQuantity});

  factory PartNumberAt.fromJson(Map json) {
    return PartNumberAt(
      partNumber: json['partNumber'],
      quantity: json['quantity'],
      initialQuantity: json['initialQuantity'],
   );
 }

}

//partnumber RawMaterial
class ReelPartNumber {
  final PartNumberAt partNumberAt;

  ReelPartNumber({required this.partNumberAt});

  factory ReelPartNumber.fromJson(Map json) {
    return ReelPartNumber(
      partNumberAt: PartNumberAt.fromJson(json['attributes']),
    );
  }
}

class ReelLpn {
   Attributes? attributes;
   ReelPartNumber? reelPartNumber;

  ReelLpn(
      {required Attributes attributes, required ReelPartNumber reelPartNumber});

  factory ReelLpn.fromJson(Map json) {
    return ReelLpn(
      attributes: Attributes.fromJson(json['attributes']),
      reelPartNumber: ReelPartNumber.fromJson(json['RawMaterial']),
    );
  }
}

and I have a file where I make http requests, the request returns the following

{
"attributes": {
    "itemId": "0605007783",
    "itemKey": "14992663",
    "itemType": "REEL",
    "itemTypeClass": "Component Lot",
    "containerId": "FA0210AEF424292",
    "locationInContainer": "B",
    "toolContainerId": "SMT6",
    "locationInTool": "10004-B",
    "quarantineLocked": "false",
    "expired": "false",
    "initTmst": "2022-01-20T09:40:30.969-03:00"
},
"RawMaterial": {
    "attributes": {
        "partNumber": "11201312001166",
        "partNumberDesc": "",
        "supplierId": "DEFAULT",
        "quantity": "2497.0",
        "initialQuantity": "5000.0",
        "rejectedQuantity": "3.0",
        "manualAdjustmentQuantity": "548.0"
    },
}

and the request is made as follows

Future<ReelLpn?> getReelData(String lpn) async {
http.Response response = await http.get(Uri.parse(apiUrl '/$lpn'));

if (response.statusCode == 200) {
  Map data = (json.decode(response.body)); //conver to json
  print(data);
  ReelLpn reelLpn = ReelLpn.fromJson(data); //transform json to ReelLpn
  return reelLpn;
} 
return null; 

}

and I call the service as follows

ReelLpn? data = await CogiscanService().getReelData('0605007783');
  print(data?.attributes?.type);

my problem starts there, when I print

print(data?.attributes?.type); 

it returns null, I put several prints, in the ReelL class, Attributes and PartNumber, to see if I was reading the Map correctly, and they definitely read correctly.

So why when I want to access any of the fields does it return null?

CodePudding user response：

Change your ReelLpn Constructor. you are not referencing the class members... thats why its always null.

ReelLpn({required this.attributes, required this.reelPartNumber});