從json到物件飛鏢

下午好，我可能發現了一個小錯誤，但是直到現在我才弄清楚..我在dart中有以下類，該類的目的是接收json并將每個欄位轉換為物件

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']),
    );
  }
}

我有一個檔案，我在其中發出 http 請求，請求回傳以下內容

{
"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"
    },
}

請求如下

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; 

}

我按如下方式呼叫服務

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

我的問題從那里開始，當我列印時

print(data?.attributes?.type); 

它回傳 null，我在 ReelL 類、Attributes 和 PartNumber 中放置了幾個列印件，以查看我是否正確讀取了 Map，并且它們肯定讀取正確。

那么為什么當我想訪問任何欄位時它會回傳 null 呢？

uj5u.com熱心網友回復：

更改您的 ReelLpn 建構式。你沒有參考班級成員......這就是為什么它總是為空。

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

標籤：json 扑 镖

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