copyWith gives error when creating functions in provider

I am learning to use StateNotifier and StateNotifierProvider from a YouTube video.

I have created a model and a StateNotifier class

User data model:

class Users {
  final String? agentId;
  final String? fName;
  final String? lName;
  final String? agency;
  final String? agencyId;
  final String? address1;
  final String? address2;
  final String? city;
  final String? state;
  final int? zipcode;
  final String? cellPhone;
  final String? officePhone;
  final String? email;
  final String? mls;
  final String? mlsId;

  Users(
      {this.cellPhone,
      this.address1,
      this.address2,
      this.agency,
      this.agencyId,
      this.agentId,
      this.city,
      this.fName,
      this.lName,
      this.officePhone,
      this.state,
      this.zipcode,
      this.mls,
      this.mlsId,
      this.email});

  Map<String, dynamic> toMap() {
    return {
      'cellPhone': cellPhone,
      'address1': address1,
      'address2': address2,
      'agency': agency,
      'agencyId': agencyId,
      'agentId': agentId,
      'city': city,
      'fName': fName,
      'lName': lName,
      'officePhone': officePhone,
      'state': state,
      'zipCode': zipcode,
      'mls': mls,
      'mlsId': mlsId,
      'email': email
    };
  }

  // pass in a map and get an object back
  Users.fromFirestore(Map<String, dynamic> firestore)
      : cellPhone = firestore['cellPhone'],
        address1 = firestore['address1'],
        address2 = firestore['address2'],
        agency = firestore['agency'],
        agencyId = firestore['agencyId'],
        agentId = firestore['agentId'],
        city = firestore['city'],
        fName = firestore['fName'],
        lName = firestore['lName'],
        officePhone = firestore['officePhone'],
        state = firestore['state'],
        zipcode = firestore['zipCode'],
        mls = firestore['mls'],
        mlsId = firestore['mlsId'],
      email = firestore['email'];
}

StateNotifier class:

class UserNotifier extends StateNotifier<Users> {
  UserNotifier(super.state); //  constructor


// **************************************************

  // functions to update class members
  void updatefName(String newfName) {
    state = state.copyWith(fName: newfName);
  }

  void updatelName(String newlName) {
    state = state.copyWith(lName: newlName);
  }

    void updateaddress1(String newaddress1) {
    state = state.copyWith(address1: newaddress1);
  }

    void updateaddress2(String newaddress2) {
    state = state.copyWith(address2: newaddress2);
  }

    void updateCity(String newCity) {
    state = state.copyWith(city: newCity);
  }

    void updateState(String newState) {
    state = state.copyWith(state: newState);
  }

    void updateZipcode(String newZipcode) {
    state = state.copyWith(zipcode: newZipcode);
  }

    void updateCellPhone(String newCellPhone) {
    state = state.copyWith(cellPhone: newCellPhone);
  }

    void updateOfficePhone(String newOfficePhone) {
    state = state.copyWith(officePhone: newOfficePhone);
  }

    void updateCompany(String newCompany) {
    state = state.copyWith(company: newCompany);
  }
  
    void updateMls(String newMls) {
    state = state.copyWith(mls: newMls);
  }
}

I am getting an error on the copyWith. Here is the error message:
The method ‘copyWith’ isn’t defined for the type ‘Users’.

I searched on the internet and one post said I don’t need .copyWith so I removed it and I got a different error on state.

I have followed the example in the video but I am getting the error. How do I get rid of the error?

Thank you for your help.

>Solution :

In your Users model you don’t have copyWith method implemented which you are using in the statenotifier class.

add the following copyWith method in your Users model.

// Define a copyWith method
Users copyWith({
String? cellPhone,
String? address1,
String? address2,
String? agency,
String? agencyId,
String? agentId,
String? city,
String? fName,
String? lName,
String? officePhone,
String? state,
int? zipcode,
String? mls,
String? mlsId,
String? email,
}) {
return Users(
  cellPhone: cellPhone ?? this.cellPhone,
  address1: address1 ?? this.address1,
  address2: address2 ?? this.address2,
  agency: agency ?? this.agency,
  agencyId: agencyId ?? this.agencyId,
  agentId: agentId ?? this.agentId,
  city: city ?? this.city,
  fName: fName ?? this.fName,
  lName: lName ?? this.lName,
  officePhone: officePhone ?? this.officePhone,
  state: state ?? this.state,
  zipcode: zipcode ?? this.zipcode,
  mls: mls ?? this.mls,
  mlsId: mlsId ?? this.mlsId,
  email: email ?? this.email,
);

}

Also, please edit the question to include the video link you are following.