未处理的异常：将对象转换为可编码对象失败：'Porder'的实例

Question

我有一个用于采购订单的类，其中包含一个变量和另一个称为采购订单详细信息的类的列表，我试图将采购订单和采购订单详细信息以对象的形式发送，并将列表从flutter ui发送到API，但是当按下调用API服务的按钮时出现了此错误，主要问题是将Porder转换为json 任何想法如何解决这个问题，在此先感谢

代码

DECODE(d.Eventstatus,
     1, 'Completed',
    10, 'Cancelled: No Show',
    -- ...
     8, 'Cancelled: Refused Treatment',
    TO_CHAR(d.Eventstatus)
 ) END AS Appt_Status

API服务

class Porder {

  int _OrVId;
  List<Pdetails> _ordersData;

  Porder(this._OrVId,this._ordersData);

  int get OrVId=> _OrVId;
  List get ordersData=> _ordersData;

  set OrVId (int newOrVId){
    _OrVId = newOrVId;
  }
  set ordersData (List newordersData){
    _ordersData = newordersData;
  }

   Map<String,dynamic> toMap(){
    var map=Map<String,dynamic>();
    map["OrVId"]=_OrVId;
    map["ordersData"]=_ordersData;
   
    return map;
   }

   Porder.fromObject(dynamic o){
    this._OrVId=o["OrVId"];
    this._ordersData=o["ordersData"];
    
  }


}



class Pdetails {

  int _OrIId;
  double _OrPrice;
  int _OrQ;
  
  Pdetails(this._OrIId,this._OrPrice,this._OrQ);

  int get OrIId=> _OrIId;
  double get OrPrice=> _OrPrice;
  int get OrQ=> _OrQ;

  set OrIId (int newOrIId){
    _OrIId = newOrIId;
  }
  set OrPrice (double newOrPrice){
    _OrPrice = newOrPrice;
  }
  set OrQ (int newOrQ){
    _OrQ = newOrQ;
  }

   Map<String,dynamic> toMap(){
    var map=Map<String,dynamic>();
    map["OrIId"]=_OrIId;
    map["OrPrice"]=_OrPrice;
    map["OrQ"]=_OrQ;
   
    return map;
   }

   Pdetails.fromObject(dynamic o){
    this._OrIId=o["OrIId"];
    this._OrPrice=o["OrPrice"];
    this._OrQ=o["OrQ"];
  }

}

按钮

  Future saveOrderData (Porder order) async
  {
    var neworder = order.toMap();
    var registerBody = json.encode(neworder);
    print(neworder);
    var res = await http.post(SPorders+"/saveOrder", headers:header, body:registerBody);
  }