您有几种选择，具体取决于您如何构建应用程序或在哪里拥有中心状态。

我在这里为您提出一种更新本地地图变量的解决方案。或者，您可以将事件/流发送到商店所在的地方。

import 'package:flutter/material.dart';

void main() => runApp(new MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  List<Item> itemList = [
    Item("ID1", "First product"),
    Item("ID2", "Second product"),
  ];

  Map<String, int> quantities = {};

  void takeNumber(String text, String itemId) {
    try {
      int number = int.parse(text);
      quantities[itemId] = number;
      print(quantities);
    } on FormatException {}
  }

  Widget singleItemList(int index) {
    Item item = itemList[index];

    return Container(
      decoration: BoxDecoration(
        color: Colors.white,
      ),
      child: Row(
        children: [
          Expanded(flex: 1, child: Text("${index + 1}")),
          Expanded(
            flex: 3,
            child: TextField(
              keyboardType: TextInputType.number,
              onChanged: (text) {
                takeNumber(text, item.id);
              },
              decoration: InputDecoration(
                labelText: "Qty",
              ),
            ),
          ),
        ],
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text("Demo")),
      body: Center(
        child: ListView.builder(
            shrinkWrap: true,
            itemCount: itemList.length,
            itemBuilder: (context, index) {
              if (itemList.isEmpty) {
                return CircularProgressIndicator();
              } else {
                return singleItemList(index);
              }
            }),
      ),
    );
  }
}

class Item {
  final String id;
  final String name;

  Item(this.id, this.name);
}