Is there a way to compare two list and check for the value that are the same - firebase

Question

I am create a social media type app I want to create a follower and following list like Instagram, I want when I go on some else profile and click on their followers or following list it shows a list of all the users that is following that person and if I am also following someone in the list it give me the option to unfollow that person and if I am not following the same person it gives me the option to follow them.
The code below is what I was to check if I am following any one in profile user followers list, What I have done is I query the data from firestore of all the user id the I am following and the same for user profile that is currently open and store the list in two separate variable and what it should do is check both list and if a user Id is in both list it means I am also following that user and should show that I am following that user and give the option to unfollow but what happens is instead of showing that I am only following the user who's id is in both list it show that I am following every one.
checkfollowers(BuildContext context, String? id) async {
final auth = Provider.of<AuthState>(context, listen: false);
List<String> followingList = [];
List<String> myFollowingList = [];
try {
final QuerySnapshot following = await _firestore
.collection('following')
.doc(auth.getCurrentUser.uid)
.collection('userFollowing')
.get();
QuerySnapshot userfollowing = await _firestore
.collection('followers')
.doc(id)
.collection('userFollowers')
.get();
following.docs.forEach((element) {
myFollowingList.add(element.id);
});
userfollowing.docs.forEach((element) {
followingList.add(element.id);
});
// followingList.where((item) => myFollowingList.contains(item));
check(value) => myFollowingList.contains(value);
isFollowedByMe = followingList.any(check);
notifyListeners();
print(followingList);
print(myFollowingList);
} catch (err) {
print(err.toString() + 'this error is coming from profileState');
}
}
below code is how I build the follower/following list
final FirebaseFirestore _firestore = FirebaseFirestore.instance;
UserModel? users;
#override
void initState() {
final profileState = Provider.of<ProfileState>(context, listen: false);
profileState.checkfollowers(context, widget.proFileId);
super.initState();
}
userComponent(UserModel? model, BuildContext context) {
final profileState = Provider.of<ProfileState>(context);
final auth = Provider.of<AuthState>(context);
return Container(
margin: EdgeInsets.symmetric(horizontal: 10),
padding: EdgeInsets.only(top: 10, bottom: 10),
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: [
GestureDetector(
onTap: () {
Navigator.push(
context,
MaterialPageRoute(
builder: (context) =>
ProfilePage(profileId: '${model?.userId}'),
),
);
},
child: Row(
children: [
Container(
width: 60,
height: 60,
child: CircleAvatar(
radius: 50,
backgroundImage: NetworkImage('${model?.profilePic}'),
),
),
SizedBox(width: 10),
Column(
crossAxisAlignment: CrossAxisAlignment.start,
mainAxisSize: MainAxisSize.min,
children: [
Text('${model?.userName}',
style: TextStyle(
color: Colors.black, fontWeight: FontWeight.w500)),
SizedBox(
height: 5,
),
Text(
'${model?.displayName}',
style: TextStyle(
color: Colors.grey[500],
),
),
],
)
],
),
),
auth.getCurrentUser.uid == model?.userId
? Container()
: GestureDetector(
onTap: () {
if (auth.getCurrentUser.uid == model?.userId) {
print('you can not follow your self');
} else if (profileState.isFollowedByMe == true) {
profileState.setIsFollowedByMeToFalse();
profileState.handleUnFollow(context, model?.userId);
} else if (profileState.isFollowedByMe == false) {
profileState.setIsFollowedByMeToTrue();
profileState.handleFollow(context, model?.userId);
}
},
child: AnimatedContainer(
height: 35,
width: 110,
duration: Duration(milliseconds: 300),
decoration: BoxDecoration(
color: profileState.isFollowedByMe == true
? AppColors.white
: AppColors.pinkaccent,
borderRadius: BorderRadius.circular(5),
border: Border.all(
color: Colors.grey.shade700,
),
),
child: Center(
child: Text(
profileState.isFollowedByMe == true
? 'UnFollow'
: 'Follow',
style: TextStyle(
color: profileState.isFollowedByMe == true
? Colors.black
: Colors.white),
),
),
),
)
],
),
);
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
elevation: 0,
backgroundColor: Colors.white,
title: Container(
height: 38,
child: TextField(
onChanged: (value) {},
decoration: InputDecoration(
filled: true,
fillColor: Colors.white,
contentPadding: EdgeInsets.all(0),
prefixIcon: Icon(
Icons.search,
color: Colors.grey.shade500,
),
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(50),
borderSide: BorderSide.none),
hintStyle: TextStyle(fontSize: 14, color: Colors.grey.shade500),
hintText: "Search users"),
),
),
),
body: StreamListWrapper(
stream: _firestore
.collection('followers')
.doc(widget.proFileId)
.collection('userFollowers')
.snapshots(),
itemBuilder: (context, DocumentSnapshot snapshot) {
var data = snapshot.data() as Map<String, dynamic>;
users = UserModel.fromJson(data);
return userComponent(users, context);
},
text: '${widget.user?.userName} as no Followers',
),
);

Answer 1

It would be simpler (and more performant) to use the Set data structure rather than List. The intersection method on Set returns the items contained in both sets.
for example:
void main() {
Set<String> followingSet = {'Jeff', 'Mike', 'Joe', 'Jess'};
Set<String> myFollowingSet = {'Jess', 'Matt', 'Mike', 'Frank'};
Set<String> usersInBothSets = followingSet.intersection(myFollowingSet);
print(usersInBothSets); // {Mike, Jess}
}