Flutter 未处理的异常：将对象转换为可编码对象失败：'；Porder&x27；

我有一个purchase order类，包含一个变量和另一个名为purchase order details的类的列表，我试图将purchase order和purchase order details以对象和列表的形式从Flatter ui发送到API，但按下调用API服务的按钮时出现此错误，主要问题是如何将Porder转换为json 你知道如何解决这个问题吗，提前谢谢

代码

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"];
  }

}

钮扣

onPressed: () async {
                List<Pdetails> pdl = new List<Pdetails>();
                for (var product in products) {
                  Pdetails pdetails = new Pdetails(product.item, product.sPrice.toDouble(), product.q);
                  
                  pdl.add(pdetails);
                }
                
                
                sOrder = apiServices();
                porder = Porder(globals.vendorid,pdl);
                final saveResponse =
                     await sOrder.saveOrderData(porder);
                // showCustomDialog(products, context);
              },```

onPressed:（）异步{
List pdl=新列表（）；
用于（产品中的var产品）{
Pdetails Pdetails=新的Pdetails（product.item，product.sPrice.toDouble（），product.q）；
pdl.add（PDE详细信息）；
}
sOrder=apiServices（）；
porder=porder（全球供应商，pdl）；
最终保存响应=
wait sOrder.saveOrderData（porder）；
//showCustomDialog（产品、上下文）；
},```

我想你会问（你怎么能很好地使用toMap！？）所以使用toMap，即返回{'first'：_OvId，'second'：_AnyThing}。。像这样试试

onPressed: () async {
                List<Pdetails> pdl = new List<Pdetails>();
                for (var product in products) {
                  Pdetails pdetails = new Pdetails(product.item, product.sPrice.toDouble(), product.q);
                  
                  pdl.add(pdetails);
                }
                
                
                sOrder = apiServices();
                porder = Porder(globals.vendorid,pdl);
                final saveResponse =
                     await sOrder.saveOrderData(porder);
                // showCustomDialog(products, context);
              },```