Question

我有一个名为Invoices的类，并且该类包含一个类List<MenuInInvoice> menus的列表。类MenuInInvoice有两个变量，分别为foodName和price。

但是在main()类中，我无法访问这些变量。

import 'dart:convert';

    import 'package:cloud_firestore/cloud_firestore.dart';

    Invoices invoicesFromJson(String str) => 
 Invoices.fromJson(json.decode(str));

    String invoicesToJson(Invoices data) => json.encode(data.toJson());

    class Invoices {
     String orderNo;
     String tableNo;
     String customerName;
     DateTime orderDate;
     List<MenuInInvoice> menus;
     DocumentReference reference;

     Invoices({
      this.orderNo,
      this.tableNo,
      this.customerName,
      this.orderDate,
      this.menus,
     });

     Invoices.fromJson(Map json,{this.reference}){
      orderNo = json["orderNo"] ?? "unknown";
      tableNo = json["tableNo"] ?? "unknown";
      customerName = json["customerName"] ?? "unknown";
      orderDate = DateTime.parse(json["orderDate"]);
      menus = new List<MenuInInvoice>.from(json["menus"].map((x) => MenuInInvoice.fromJson(x)));
     }

     Invoices.fromSnapshot(DocumentSnapshot snapshot):
        this.fromJson(snapshot.data, reference: snapshot.reference);


     Map<String, dynamic> toJson() => {
      "orderNo": orderNo ?? "unknown",
      "tableNo": tableNo ?? "unknown",
      "customerName": customerName ?? "unknown",
      "orderDate": "${orderDate.year.toString().padLeft(4, '0')}-${orderDate.month.toString().padLeft(2, '0')}-${orderDate.day.toString().padLeft(2, '0')}",
      "menus": new List<dynamic>.from(menus.map((x) => x.toJson())),
    };
  }

   class MenuInInvoice {
    String foodName;
    String price;

    MenuInInvoice({
     this.foodName,
     this.price,
    });

    factory MenuInInvoice.fromJson(Map json) => new MenuInInvoice(
     foodName: json["foodName"] ?? "unknown",
     price: json["price"] ?? "unknown",
    );

    Map<String, dynamic> toJson() => {
     "foodName": foodName ?? "unknown",
     "price": price ?? "unknown",
    };
  }

这是我的main（）类：

Invoices invoices = new Invoices(
     tableNo: "01",
     orderNo: "001",
     customerName: "Jonh",
     orderDate: DateTime.now(),
     menus.foodName: "abc"
)

在main()类中，我无法使用语句menus.foodName来访问类的变量。

我该怎么做？预先感谢！

Answer 1

代替：

Invoices invoices = Invoices(
     tableNo: orderItem.tableNo,
     orderNo: orderItem.orderNo,
     customerName: orderItem.customerName,
     orderDate: DateTime.now(),
     menus: orderItem.menus.foodName
    )

尝试：

Invoices invoices = new Invoices(
     tableNo: orderItem.tableNo,
     orderNo: orderItem.orderNo,
     customerName: orderItem.customerName,
     orderDate: DateTime.now(),
     menus: orderItem.menus.foodName
    )

Answer 2

我不确定您要达到什么目标。

Invoice构造函数有五个命名参数，其中一个称为menus。调用构造函数时，可以通过在参数名称前面加上一个冒号来传递命名参数的参数。

在您的主要代码中：

Invoices invoices = new Invoices(
  tableNo: "01",
  orderNo: "001",
  customerName: "Jonh",
  orderDate: DateTime.now(),
  menus.foodName: "abc"
)

您可以正确地将参数传递给命名参数tableNo，orderNo，customerName和orderDate。

但是语法menus.foodname: "abc"无效。没有名为menus.foodName的参数，它甚至不是有效的名称（单个标识符）。

由于您提供的代码尚不清楚，您能描述一下您期望/想要执行的代码吗？

Answer 3

您确实无法直接访问foodName。

请尝试以下操作：

List<MenuInInvoice> menuList = List<MenuInInvoice>();
menuList.add(MenuInInvoice(foodName: 'abc'));

Invoices invoices = Invoices(
    tableNo: '01',
    orderNo: '001',
    customerName: 'Jonh',
    orderDate: DateTime.now(),
    menus: menuList);

如何在Dart中访问子类的变量

3 个答案: