InhertiedWigets

inherited_widgets.dart

import 'package:collection/collection.dart';
import 'package:flutter/material.dart';


class ShoppingCartInfo {
  final List<int> productIds;

  ShoppingCartInfo({this.productIds});
}





class ShoppingCart extends InheritedWidget {
  const ShoppingCart({Key key, @required this.info, @required this.child});

  final ShoppingCartInfo info;
  final Widget child;
  @override
  bool updateShouldNotify(ShoppingCart old) => !IterableEquality().equals(info.productIds, old.info.productIds);

  static ShoppingCartInfo of(BuildContext context) {
    return (context.inheritFromWidgetOfExactType(ShoppingCart) as ShoppingCart).info;
  }
}

main_dart.dart

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter_inherted_widgets/inherited_widgets.dart';
import 'package:flutter_inherted_widgets/product_page.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ShoppingCart(info: ShoppingCartInfo(productIds: <int>[1, 2]),child: MaterialApp(
      home: ProductFeed(),
    ));
  }
}

product_detail.dart

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'inherited_widgets.dart';

class ProductDetail extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return ProductDetailState();
  }
}

class ProductDetailState extends State<ProductDetail> {
  @override
  Widget build(BuildContext context) {
     final info = ShoppingCart.of(context);
    return Scaffold(
      appBar: AppBar(title: Text('Retail Store')),
      body: Center(
        child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Text('Product A'),
              Text('${info.productIds.length} selected'),
            ]),
      ),

      floatingActionButton:  FloatingActionButton(
        child: Icon(Icons.add ),
        onPressed: (){

          setState(() {
            info.productIds.add(10);
          });
        },
      ),
    );
  }
}

product_page.dart

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter_inherted_widgets/product_detail.dart';

import 'inherited_widgets.dart';

class ProductFeed extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return ProductFeedState();
  }
}

class ProductFeedState extends State<ProductFeed> {
  @override
  Widget build(BuildContext context) {
    final info = ShoppingCart.of(context);
    return Scaffold(
      appBar: AppBar(title: Text('Product Feed')),
      body: Center(
        child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Text('${info.productIds.length} selected'),
              RaisedButton(
                child: Text('Product A'),
                onPressed: () {
                  Navigator.push( context, MaterialPageRoute(builder: (context) => ProductDetail()));
                },
              ),
            ]),
      ),

      floatingActionButton: FloatingActionButton(
        child: Icon(Icons.add ),
        onPressed: (){

setState(() {
  info.productIds.add(10);
});
        },
      ),
    );
  }
}