Code for cart.dart

import 'package:flutter_bloc/flutter_bloc.dart';

abstract class CartEvent {}

class CartAdd extends CartEvent {
  final int itemAdd;

  CartAdd(this.itemAdd);
}

class CartRemove extends CartEvent {
  final int itemRemove;

  CartRemove(this.itemRemove);
}

class CartBloc extends Bloc<CartEvent, List<int>> {
  final List<int> cartList;

  List<int> get items => cartList;

  CartBloc(this.cartList) : super([]) {
    on<CartAdd>((event, emit) {
      cartList.add(event.itemAdd);
      emit(cartList);
    });
    on<CartRemove>((event, emit) {
      cartList.remove(event.itemRemove);
      emit(cartList);
    });
  }
}

When launch the application, only on the first click a checkmark appears. and can’t take it off.
Probably problems with state

Code for BlocBuilder for widget. From state I can check contains item or no

BlocBuilder<CartBloc, List<int>>(
      builder: (context, state) => Padding(
        padding: const EdgeInsets.all(8.0),
        child: ListTile(
          leading: Icon(
            Icons.bakery_dining_outlined,
            color: Colors.primaries[itemNum % Colors.primaries.length],
          ),
          title: Text('item $itemNum'),
          trailing: IconButton(
            icon:
                // itemCart.contains(itemNum)
                context.read<CartBloc>().cartList.contains(itemNum)
                    //  cart.contains(itemNum)
                    ? const Icon(
                        Icons.check_circle,
                        color: Colors.blue,
                      )
                    : const Icon(Icons.add_circle_outline_sharp),
            onPressed: () {
              !state.contains(itemNum)
                  // !cart.contains(itemNum)
                  ? context.read<CartBloc>().add(CartAdd(itemNum))
                  : context.read<CartBloc>().add(CartRemove(itemNum));
            },
          ),
          onTap: () {},
        ),
      ),
    ),

for tab cart code is almost the same, just for delete from cart

>Solution :

To changes the state/UI you need to provide new list. You can do it like.

on<CartAdd>((event, emit) {
  cartList.add(event.itemAdd);
  emit(cartList.toList());
});
on<CartRemove>((event, emit) {
  cartList.remove(event.itemRemove);
  emit(cartList.toList());
});

Or in single line

CartBloc(this.cartList) : super([]) {
  on<CartAdd>((event, emit) {
    emit([...cartList..add(event.itemAdd)]);
  });
  on<CartRemove>((event, emit) {
    emit([...cartList..remove(event.itemRemove)]);
  });
}