test_provider.dart

import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:shared_preferences/shared_preferences.dart';

void main() {
  Firestore.instance.settings(timestampsInSnapshotsEnabled: true);
  SharedPreferences.getInstance().then((prefs) {
    runApp(MakanikaApp(prefs: prefs));
  });
}

class MakanikaApp extends StatelessWidget {
  final SharedPreferences prefs;
  MakanikaApp({this.prefs});
  @override
  Widget build(BuildContext context) {
    return MultiProvider(
      providers: [
        ChangeNotifierProvider(
          builder: (_) => MakanikaModel(),          
        ),
      ],
      child: MaterialApp(
        title: "app 1",
        theme: ThemeData(
          primaryColor: Colors.blue,
        ),
        initialRoute: '/',
        routes: {
          '/': (context) => Home(),
        },
      ),
    );
  }
}

class MakanikaModel with ChangeNotifier {
  List<Item> _requestItems = List<Item>();
  int _quantity = 0;
  set quantity(newValue) {
    _quantity = newValue;
    notifyListeners();
  }

  set requestItems(newValue) {
    _requestItems = newValue;
    notifyListeners();
  }

  //getters
  List<Item> get requestItems => _requestItems;
  int get quantity => _quantity;
}

class Item {
  int itemQty;
  final double itemPrice;
  final double itemDiscount;

  Item({
    this.itemDiscount,
    this.itemQty,
    this.itemPrice,
  });

  Map<String, Object> toJson() {
    return {
      'itemPrice': itemPrice,
      'itemQun': itemQty,
      'itemDiscount': itemDiscount,
    };
  }    
    class Home extends StatelessWidget {    
      @override
      Widget build(BuildContext context) {    
      return Scaffold(
          body:Container(
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: <Widget>[
    IconButton(
                                    icon: Icon(Icons.remove_circle,
                                        color: Colors.amber.shade500),
                                    onPressed: () {
                                      if (model.quantity >
                                          0) {
                                        model.quantity--;
                                      }
                                    },
                                  ),
    							  
    							  new IconButton(
                                    icon: Icon(Icons.remove_circle,
                                        color: Colors.amber.shade500),
                                    onPressed: () {
                                      if (itemList[ind].itemQty >
                                          0) {
                                        Provider.of<MakanikaModel>(
                                          context,
                                        ).requestItems[ind].itemQty--;
                                      }
                                    },
                                  )
              ],
            ),            
          ),  
        );
      }
    }