basic_futter_app/lib/product_manager.dart

import 'package:flutter/material.dart';

import './products.dart';

class ProductManager extends StatefulWidget {
  final String startingProduct;

  ProductManager(this.startingProduct);

  @override
  State<StatefulWidget> createState() {
    return _ProductManagerState();
  }
}

class _ProductManagerState extends State<ProductManager> {
  List<String> _products = [];

  @override
  void initState() {
    super.initState();
    _products.add(widget.startingProduct);    
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Container(
          margin: EdgeInsets.all(10),
          child: RaisedButton(
            onPressed: () {
              setState(() {
                _products.add('Advanced Food Tester');
              });
            },
            child: Text('Click Me!'),
          ),
        ),
        Products(_products),
      ],
    );
  }
}