list - flutter : The method 'add' was called on null

Question

我有一个应用程序尝试使用提供商将产品添加到卡中，首先我有这个产品模型:

class Products {
  final String item;
  final int price;    
  Products({this.item, this.price});
}

然后我有这个小部件来查看产品列表，它显示成功:

import './service/provider.dart';
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';    
import 'models/products.dart';    
class ProductList extends StatelessWidget {
  @override
  List<Products> myProducList;
  Widget build(BuildContext context) {
    myProducList = [
      Products(item: 'Car', price: 20000),
      Products(item: 'PC', price: 500),
      Products(item: 'LapTop', price: 750),
      Products(item: 'House', price: 25000),
    ];
    return Scaffold(
      body: ListView.builder(
          shrinkWrap: true,
          itemCount: myProducList.length,
          itemBuilder: (context, index) {
            return Card(
              child: ListTile(
                title: Text(myProducList[index].item),
                subtitle: Text(myProducList[index].price.toString()),
                trailing: IconButton(
                  icon: Icon(Icons.add),
                  onPressed: () {
                    Provider.of<MyProv>(context, listen: false).add_item(
                    myItem: myProducList[index].item,
                    myPrice: myProducList[index].price);
                  },
                ),
              ),
            );
          }),
    );
  }
}

我也有这个供应商:

class MyProducts {
  final String item;
  final int price;

  MyProducts({this.item, this.price});
}

class MyProv with ChangeNotifier {
  List<MyProducts> product;

  void add_item({String myItem, int myPrice}) {
    product.add(MyProducts(
      item: myItem,
      price: myPrice,
    ));
    notifyListeners();
  }
    }

按下按钮时出现此错误:

The method 'add' was called on null.
Receiver: null
Tried calling: add(Instance of 'MyProducts')

我该如何解决？

Answer 1

您还没有真正创建一个列表。

改变

List<MyProducts> product;

对此

List<MyProducts> product = [];