Concept of List StateUp in Dart Similar to adding Listiner in Android

main.dart

import 'package:flutter/material.dart';

import './product_manager.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(
          brightness: Brightness.light,
          primarySwatch: Colors.deepOrange,
          accentColor: Colors.deepPurple),
      home: Scaffold(
        appBar: AppBar(
          title: Text('EasyList'),
        ),
        body: ProductManager(startingProduct: 'Food Tester'),
      ),
    );
  }
}

product_control.dart

import 'package:flutter/material.dart';

class ProductControl extends StatelessWidget {
  final Function addProduct;

  ProductControl(this.addProduct);

  @override
    Widget build(BuildContext context) {
      return RaisedButton(
            color: Theme.of(context).primaryColor,
            onPressed: () {
              //Here in this class we called addProducts without any need of setState()
              addProduct('Sweets');
            },
            child: Text('Add Product'),
          );
    }
}

product_manager.dart

import 'package:flutter/material.dart';

import './products.dart';
import './product_control.dart';

class ProductManager extends StatefulWidget {
  final String startingProduct;

  ProductManager({this.startingProduct = 'Sweets Tester'}) {
    print('[ProductManager Widget] Constructor');
  }

  @override
  State<StatefulWidget> createState() {
    print('[ProductManager Widget] createState()');
    return _ProductManagerState();
  }
}

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

  @override
  void initState() {
    print('[ProductManager State] initState()');
    _products.add(widget.startingProduct);
    super.initState();
  }

  @override
  void didUpdateWidget(ProductManager oldWidget) {
    print('[ProductManager State] didUpdateWidget()');
    super.didUpdateWidget(oldWidget);
  }

  void _addProduct(String product) {
    //this method will be called on build method and the moment the constructer of Product class get called we add item on addition
    setState(() {
      _products.add(product);
    });
    print(_products);
  }

  @override
  Widget build(BuildContext context) {
    print('[ProductManager State] build()');
    return Column(
      children: [
        Container(
          margin: EdgeInsets.all(10.0),
          child: ProductControl(_addProduct),
        ),
        Products(_products)
      ],
    );
  }
}

products.dart

import 'package:flutter/material.dart';

class Products extends StatelessWidget {
  final List<String> products;

  Products([this.products = const []]) {
    print('[Products Widget] Constructor');
  }

  @override
  Widget build(BuildContext context) {
    print('[Products Widget] build()');
    return Column(
      children: products
          .map(
            (element) => Card(
                  child: Column(
                    children: <Widget>[
                      Image.asset('assets/food.jpg'),
                      Text(element)
                    ],
                  ),
                ),
          )
          .toList(),
    );
  }
}