DropDownButton doesn't work after using Navigator.push - flutter

Question

I'm trying to create a clothes E-Shop app and I need the cart items to show the list of different colors for each product, I'm using a DropDownButton to show them, the slidable library to create the cart items, and a custom bottom bar. If I tap in the cart item to go to the product view and then go back to the cart pressing the back button, the dropdownbutton stops working, but if I go to the product through the bottom bar everything works.
class CartPage extends StatefulWidget {
const CartPage({Key? key}) : super(key: key);
#override
CartPageState createState() => CartPageState();
}
class CartPageState extends State<CartPage> {
List<String> dropDownValues = cart.itemList.keys.toList();
late String dropDownValueShow;
final textController = TextEditingController();
#override
Widget build(BuildContext context) {
debugPrint('$dropDownValues');
dropDownValueShow = cart.itemList.isEmpty ? '' : dropDownValues[0];
return Scaffold(
bottomNavigationBar: CustomBottomNavBar(
1,
key: ValueKey(cart.itemList),
),
appBar: AppBar(
elevation: 0,
backgroundColor: Colors.black,
title: const Text(
"Shopping Cart",
style: TextStyle(color: Colors.white, fontSize: 17),
),
),
body: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: cart.empty
? [
SizedBox(
width: 200,
height: 200,
child: Center(
child: Text(
"Empty Cart",
textAlign: TextAlign.center,
style: TextStyle(
color: Colors.grey.shade500,
fontSize: 20,
),
),
))
]
: [
Expanded(
child: AnimatedList(
scrollDirection: Axis.vertical,
initialItemCount: cart.itemList.length,
itemBuilder: (context, index, animation) {
return Slidable(
key: UniqueKey(),
actionPane: const SlidableDrawerActionPane(),
actionExtentRatio: 0.25,
actions: const [],
secondaryActions: const [],
child: _cartItem(),
);
},
),
),
],
),
);
}
Widget _cartItem() {
return GestureDetector(
key: UniqueKey(),
onTap: () {
FocusScope.of(context).requestFocus(FocusNode());
Navigator.push(
context,
PageRouteBuilder(
pageBuilder: (context, animation1, animation2) =>
const ProductView(),
transitionDuration: Duration.zero,
reverseTransitionDuration: Duration.zero,
),
).then((_) => setState(() {}));
},
child: Container(
padding: const EdgeInsets.symmetric(horizontal: 10),
decoration: BoxDecoration(
color: Colors.white,
boxShadow: [
BoxShadow(
color: Colors.grey.shade200,
offset: const Offset(0, 2),
blurRadius: 6,
),
],
),
child: Row(
children: <Widget>[
Text('prod1'),
const SizedBox(
width: 10,
),
Expanded(
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
const SizedBox(height: 10),
DropdownButton(
isExpanded: true,
value: dropDownValueShow,
icon: const Icon(Icons.arrow_drop_down),
items: cart.itemList.keys.toList().map((String value) {
return DropdownMenuItem(
value: value,
child: Text(value),
);
}).toList(),
onChanged: (String? newValue) {
setState(() {
dropDownValueShow = newValue!;
});
},
),
const SizedBox(height: 10),
],
),
),
const SizedBox(
width: 10,
),
],
),
),
);
}
}
The whole code is in https://github.com/nicoacevedor/minimal.git