Add or Remove Method not working while working with Field-Array

I want to add or remove members in a group chat app. For that I have a list of users. Here is my code:

QuerySnapshot<Map<String, dynamic>>? searchResultSnapshot;
  QuerySnapshot<Map<String, dynamic>>? Snapshot;
  bool isLoading = false;
  bool haveUserSearched = false;
  bool isChecked = false;
  DatabaseMethods databaseMethods = new DatabaseMethods();
  var searchEditingController = TextEditingController();

  InitiateSearch() async {
    if (searchEditingController.text.isNotEmpty) {
      setState(() {
        isLoading = true;
      });
      await databaseMethods.GetUserByUsername(searchEditingController.text)
          .then((snapshot) {
        searchResultSnapshot = snapshot;
        print("$searchResultSnapshot");
        setState(() {
          isLoading = false;
          haveUserSearched = true;
        });
      });
    }
  }

  GetUsersList() async {
    if (searchEditingController.text.isEmpty) {
      setState(() {
        isLoading = true;
      });
      await databaseMethods.GetUsers().then((snapShot) {
        Snapshot = snapShot;
        setState(() {
          isLoading = false;
          haveUserSearched = false;
        });
      });
    }
  }

  addremovemember(userName){
    print('caa');
    final docRef = FirebaseFirestore.instance.collection("groups").doc(widget.groupRoomId);
    docRef.snapshots().listen((datasnapshot){
      if (datasnapshot.data()!.containsValue("$userName")){
        FirebaseFirestore.instance
            .collection('groups')
            .doc(widget.groupRoomId)
            .update({"users" : FieldValue.arrayRemove([userName])});
      }
      else{
        FirebaseFirestore.instance
            .collection('groups')
            .doc(widget.groupRoomId)
            .update({"users" : FieldValue.arrayUnion([userName])});
      }
    });
  }

  Widget UserList() {
    return Expanded(
      child: isLoading
          ? Container(
              child: Center(
                child: CircularProgressIndicator(),
              ),
            )
          : haveUserSearched
              ? ListView.builder(
                  itemCount: searchResultSnapshot?.docs.length,
                  itemBuilder: (context, index) {
                    return Listtile(
                      searchResultSnapshot?.docs[index].data()["userName"],
                      searchResultSnapshot?.docs[index].data()["userEmail"],
                    );
                  })
              : ListView.builder(
                  itemCount: Snapshot?.docs.length,
                  itemBuilder: (context, index) {
                    return Listtile(
                      Snapshot?.docs[index].data()["userName"],
                      Snapshot?.docs[index].data()["userEmail"],
                    );
                  }),
    );
  }

  Widget Listtile(String? userName, String? userEmail) {
    return ListTile(
        title: Text(userName ?? "",
            style: TextStyle(color: Colors.white, fontSize: 16)),
        subtitle: Text(
          userEmail ?? "",
          style: TextStyle(color: Colors.white, fontSize: 16),

        ),
        onTap: () => (){addremovemember(userName); print("FHFGFH");},
      );
  }

Now when I tap list-tile it is not printing any thing. I think it means that there is some problem with onTap method and that is why addremovemember( ) is never called. I don't know where the main problem lies. Please help me out with this.