auto_update_products_concept.dart

import 'package:flutter/material.dart';

const Color darkBlue = Color.fromARGB(255, 18, 32, 47);



final List<Product> products = [
    Product(name: 'Potato', quantity: '100', value: 1000),
    Product(name: 'Pie', quantity: '100', value: 1500),
];

///ViewModel/Provider
double total = 0;
//////
void main() {
  
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.dark().copyWith(
        scaffoldBackgroundColor: darkBlue,
      ),
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: ListView.builder(
          itemBuilder: (context, index){
            return ProductTile(product: products[index], onChanged: (amount){
              products[index].value = amount;
              calculateTotal(products);
            });
          },
          itemCount: products.length,
        ),
      ),
    );
  }
  
  ///View Model
  void calculateTotal(List<Product> products){
    total = 0;
    for(var product in products){
      total += product.value;
    }
    notifyListeners();
  }
  
  
  ///Fake data
  notifyListeners(){}
}

class Product{
  String name;
  String quantity;
  double value;
  
  Product({required this.name, required this.quantity, required this.value});
  
  factory Product.fromMap(Map<String, dynamic> map)=>
    Product(
      name: map['name'], 
      quantity: map['quantity'], 
      value: map['value']);
}

class ProductTile extends StatefulWidget {
  final ValueChanged<double>? onChanged;
  final Product product;

  const ProductTile({Key? key, this.onChanged, required this.product}) : super(key: key);
  
  @override
  State<ProductTile> createState() => _ProductTileState();
}

class _ProductTileState extends State<ProductTile> {
  @override
  Widget build(BuildContext context) {
    return TextField(
      onChanged: (value){
        widget.onChanged?.call(double.tryParse(value)??0.0);
      }
    );
  }
}