A value of type 'Null' can't be assigned to a parameter of type 'String' in a const constructor. Try using a subtype, or removing the keyword 'const' - firebase

Question

const homeScreenItems = [
FeedScreen(),
SearchScreen(),
AddPostScreen(),
Text('notification'),
ProfileScreen(uid: FirebaseAuth.instance.currentUser!.uid),
];
above code is my global variable page.
I want to pass uid I stored in Firestore to ProfileScreen() but I am getting the above titled error i.e A value of type 'Null' can't be assigned to a parameter of type 'String' in a const constructor. Try using a subtype, or removing the keyword 'const'.
I have declared uid as final in my ProfileScreen() but still I am getting the above error
//here is the code of ProfileScreen()
class ProfileScreen extends StatefulWidget {
final String uid;
const ProfileScreen({Key? key,required this.uid}) : super(key: key);
#override
_ProfileScreenState createState() => _ProfileScreenState();
}
class _ProfileScreenState extends State<ProfileScreen> {
var userData = {};
#override
void initState() {
getUserData();
super.initState();
}
getUserData() async {
try {
var snap = await FirebaseFirestore.instance
.collection('users')
.doc(widget.uid)
.get();
setState(() {
userData = snap.data()!;
});
} catch (e) {
showSnakBar(e.toString(), context);
}
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
backgroundColor: mobileBackgroundColor,
title: Text(userData['name']),
centerTitle: false,
),
body: ListView(
children: [
Padding(
padding: const EdgeInsets.all(16.0),
child: Column(
children: [
Row(
children: [
CircleAvatar(
radius: 40,
backgroundImage: NetworkImage(
'https://images.unsplash.com/photo-1647185255712-b5b8687b2a25?ixlib=rb-1.2.1&ixid=MnwxMjA3fDB8MHxwaG90by1wYWdlfHx8fGVufDB8fHx8&auto=format&fit=crop&w=1722&q=80',
),
),
Expanded(
flex: 1,
child: Column(
children: [
Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
mainAxisSize: MainAxisSize.max,
children: [
buildStatColumn(20, 'posts'),
buildStatColumn(150, 'followers'),
buildStatColumn(10, 'following'),
],
),
Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: [
FollowButton(
backgroundColor: mobileBackgroundColor,
borderColor: Colors.grey,
text: 'Edit Profile',
textColor: primaryColor,
function: () {},
),
],
),
],
),
),
],
),
Container(
alignment: Alignment.centerLeft,
child: Padding(
padding: const EdgeInsets.only(top: 15),
child: Text(
'username',
style: TextStyle(fontWeight: FontWeight.bold),
),
),
),
Container(
alignment: Alignment.centerLeft,
child: Padding(
padding: const EdgeInsets.only(top: 1),
child: Text('some bio'),
),
),
],
),
),
const Divider(),
],
),
);
}
Column buildStatColumn(int num, String lable) {
return Column(
mainAxisSize: MainAxisSize.min,
mainAxisAlignment: MainAxisAlignment.center,
children: [
Text(
num.toString(),
style: const TextStyle(
fontSize: 18,
fontWeight: FontWeight.bold,
),
),
Container(
margin: const EdgeInsets.only(top: 4),
child: Text(
lable,
style: const TextStyle(
fontSize: 15,
fontWeight: FontWeight.w400,
color: Colors.grey,
),
),
),
],
);
}
}

Answer 1

The issue here is that you're using const in homeScreenItems - this sets the variable constant during compile-time and can't be changed. It's usually used for fixed values like Text widgets with fixed String values.
Also, utilizing the bang (!) operator doesn't guarantee that the value won't be null. This only assures the compiler that the value is not null.
Depending on your use-case, you can remove the const from homeScreenItems and add ProfileScreen() once the user has signed-in and you're able to fetch FirebaseAuth.instance.currentUser.
List homeScreenItems = [
FeedScreen(),
SearchScreen(),
AddPostScreen(),
Text('notification'),
];
...
if(FirebaseAuth.instance.currentUser != null){
homeScreenItems.add(ProfileScreen(uid: FirebaseAuth.instance.currentUser!.uid));
}