如何处理 API 响应模型 class 如果对象在某些情况下在相同 API Flutter Dart 上不可用

Question

我需要有关 API 响应处理的帮助。我创建了模型 class 来转换 API res。我的问题是类型 API 响应已更改，例如

如果类型='Application'

 {
        "status": "success",
        "message": "Active loan Fetched",
        "data": {
            "Application": {
                "id": "",
                "coapp_status": null,
                "status": "pending-document",
                "approved_amount": "3000",
                "processing_fees": "450",
            },
            "type": "Application"
        },
        "timestamp": "2022-05-07 13:05:36",
        "require_update": "yes"
    }

并且如果类型 = 'Loan'

  {
        "status": "success",
        "message": "Loan Fetched",
        "data": {
            "Loan": {
                "id": "",
                "policy_id": "",
                "application_id": "",
                "user_id": "",
                "approved_amount": "8000",
                "disbursment_amount": "6552",
                "processing_fees": "1200",
                "interest_rate": "480",
                "pre_emi_interest": "31.5616",
                "totalAmount": 8480,
                "gst_processing_fees": 216,
                "totalDisbursment": 6552.4384,
                "current_emi_date": "10 Jun 22",
                "current_emi_amount": "5088",
                "current_emi_id": "51298",
                
                "viewid": "",
                "customermessage": "Your loan have been approved for Rs.8000"
            },
            "type": "Loan"
           
     
    }

在数据中Class对象将根据类型改变

错误日志：

Unhandled Exception: type 'Null' is not a subtype of type 'Map<String, dynamic>'

型号Class:

  Application? application;
  Loan? loan;
  String? type;
  String? sanctionLetter;

  factory Data.fromJson(Map<String?, dynamic> json) => Data(
        application: Application.fromJson(json["Application"]), => **Error if application not Found**
        loan: Loan.fromJson(json["Loan"]), **Error if Loan not found**
        type: json["type"],
        sanctionLetter: json["sanction_letter"],
      );

  Map<String?, dynamic> toJson() => {
        "Application": application!.toJson(),
        "Loan": loan!.toJson(),
        "type": type,
        "sanction_letter": sanctionLetter,
      };
}

Answer 1

我认为问题出在空检查中：

factory Data.fromJson(Map<String?, dynamic> json) => Data(
        application: json["Application"] ? Application.fromJson(json["Application"]) : null, // **Because it can be null**
        loan: json["Loan"] ? Loan.fromJson(json["Loan"]) : null, // **Because it can be null**
        type: json["type"],
        sanctionLetter: json["sanction_letter"],
      );

更新

application: json["Application"] != null ? Application.fromJson(json["Application"]) : null, // **Because it can be null**
loan: json["Loan"] != nul ? Loan.fromJson(json["Loan"]) : null,

抱歉之前的回答，我忘了检查空值

如何处理 API 响应模型 class 如果对象在某些情况下在相同 API Flutter Dart 上不可用

How to Handle API response model class if object is not Available in some situation on Same API Flutter Dart

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