I am having trouble removing an item in a list after adding the element.

  List<CartItem> _items = [];
  FirebaseFirestore? _instance;

  void add(BuildContext context, CartItem item) {
    _items.add(item);

    AuthService authService = Provider.of<AuthService>(context, listen: false);
    Map<String, dynamic> cartMap = Map();
    _items.forEach((CartItem item) {
      cartMap['title'] = (item.product as Product).title;
      cartMap['name'] = (item.product as Product).name;
    });

    _instance = FirebaseFirestore.instance;
    _instance!
        .collection('cart')
        .doc(authService.getCurrentUser()) //need to get logged in account's id
        .update({
      'cartProduct': FieldValue.arrayUnion([cartMap])
    }).then((value) {
      print(_items.length);
      notifyListeners();
    });
  }


  void remove(BuildContext context, CartItem item) {
    _items.remove(item);

    AuthService authService = Provider.of<AuthService>(context, listen: false);
    Map<String, dynamic> cartMap = Map();
    cartMap['title'] = (item.product as Product).title;
    cartMap['name'] = (item.product as Product).name;
    _instance = FirebaseFirestore.instance;
    _instance!.collection('cart').doc(authService.getCurrentUser()).update({
      'cartProduct': FieldValue.arrayRemove([cartMap]),
    }).then((value) {

      print(_items.length);
      notifyListeners();
    });
  }

After I do add(context, widget.product) and print _items.length, the result is 1 However, after I do remove(context, widget.product) and print _items.length, the result is still 1.

Consumer<CartService>(
            builder: (context, cart, child) {
              Widget renderedButton;
              if (cart.isProductAddedToCart(widget.product) == false) {
                renderedButton = DefaultButton(
                  text: "Participate",
                  press: () {
                    print(cart.isProductAddedToCart(widget.product));
                    cartService.add(context, CartItem(product: widget.product));
                    print(cart.isProductAddedToCart(widget.product));
                  },
                );
              } else {
                renderedButton = DefaultButton(
                  text: "Delete",
                  press: () {
                    print(cart.isProductAddedToCart(widget.product));
                    cartService.remove(
                        context, CartItem(product: widget.product));
                    print(cart.isProductAddedToCart(widget.product));
                  },
                );
              }
              return renderedButton;

As in the code above, the remove() method is supposed to remove the same item that was added to the list using the add() method.

CodePudding user response：

Just update the remove() to: (only change _items.remove(item); position)

void remove(BuildContext context, CartItem item) {

AuthService authService = Provider.of<AuthService>(context, listen: false);
Map<String, dynamic> cartMap = Map();
cartMap['title'] = (item.product as Product).title;
cartMap['name'] = (item.product as Product).name;
_instance = FirebaseFirestore.instance;
_instance!.collection('cart').doc(authService.getCurrentUser()).update({
  'cartProduct': FieldValue.arrayRemove([cartMap]),
}).then((value) {

/// todo check firebase collection's deletion success first
_items.remove(item);

  print(_items.length);
  notifyListeners();
});
}

CodePudding user response：

The item you're adding to the list may not be the same instance of the item you're removing. Make sure the item object/class have equality and hashcode implementation to compare the two items properly.

If you don't have control over the object, the following approach can be an easier alternative:

_items.removeWhere((_item) => _item.property == item.property);

^ where property can be the id of the product.