I was making a simple cart app, it did well but cart count not showing when app is closed and reopened again.

I am using provider and calls fetchCartProducts() method when the app is opened. It calls fine. but cart badge widget itemcount is not changing at first time. only shows 0 at first time.

  Future<void> fetchCartProducts() async {
    final dataList = await DBHelper.getData('cart_food');

//convert dataList to  _cartItems

    final entries = dataList
        .map((item) => CartModel(
              item['id'],
              item['price'].toDouble(),
              item['productName'],
              item['quantity'],
            ))
        .map((cart) => MapEntry(cart.id, cart));

    _cartItems = Map<String, CartModel>.fromEntries(entries);
    print('inside fetchcart');
  }

class HomeScreen extends StatefulWidget 
{

  @override
  _HomeScreenState createState() => _HomeScreenState();

}

class _HomeScreenState extends State<HomeScreen> 
{

  Future<List<FoodItem>> _foodItems;
  var _isInit = true;

  @override
  void initState() {
    super.initState();
    _foodItems = ApiService.getFoodItems();
    Provider.of<CartProvider>(context, listen: false).fetchCartProducts();
    setState(() {});
  }

  @override
  void didChangeDependencies() 
  {

    if (_isInit) {
      Provider.of<CartProvider>(context).fetchCartProducts();
      _isInit = false;
      setState(() {});
    }
    super.didChangeDependencies();
  }

  @override
  Widget build(BuildContext context) {
    final cart = Provider.of<CartProvider>(context, listen: false);

    return Scaffold(
      appBar: AppBar(
        title: const Text('Food Cart'),
        actions: [
//this is not updating when the app is closed and opened again.
          Consumer<CartProvider>(
            builder: (_, cartprovider, ch) => Badge(
              child: ch,
              value: cartprovider.itemCount.toString(),
            ),
            child: IconButton(
              icon: Icon(Icons.shopping_cart),
              onPressed: () {
                Navigator.push(
                  context,
                  MaterialPageRoute(builder: (_) {
                    return CartScreen();
                  }),
                );
              },
            ),
          ),
        ],
      ),
      body: FutureBuilder<List<FoodItem>>(
        future: _foodItems,
        builder: (conext, snapshot) => !snapshot.hasData
            ? const Center(
                child: CircularProgressIndicator(),
              )
            : ListView.builder(
                itemCount: snapshot.data.length,
                itemBuilder: (context, index) {
                  FoodItem foodItem = snapshot.data[index];
                  return ListTile(
                    title: Text(foodItem.productName),
                    subtitle: Text(foodItem.variant),
                    trailing: IconButton(
                      onPressed: () {
                        cart.addToCart(
                          foodItem.storeid.toString(),
                          foodItem.productName,
                          1,
                          foodItem.price,
                        );
                        setState(() {});
                      },
                      icon: const Icon(Icons.shopping_cart),
                    ),
                  );
                },
              ),
      ),
    );
  }
}

otherwise when item added to cart, it working fine. the data loss when reopened. how to get total count when the app starts?

CodePudding user response：

In order to rebuild Consumer you need to call notifyListeners() inside your CartProvider

Add notifyListeners() to your fetchCartProducts() after assigning the value to _cartItems = Map<String, CartModel>.fromEntries(entries);

Future<void> fetchCartProducts() async {
    final dataList = await DBHelper.getData('cart_food');

//convert dataList to  _cartItems

    final entries = dataList
        .map((item) => CartModel(
              item['id'],
              item['price'].toDouble(),
              item['productName'],
              item['quantity'],
            ))
        .map((cart) => MapEntry(cart.id, cart));

    _cartItems = Map<String, CartModel>.fromEntries(entries);
    notifyListeners(); // <------- this line
    print('inside fetchcart');
  }