JoinFriendViewController.swift

func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    let uid = resultsArray[indexPath.row]

    userRef.child(uid).child("locked").observeSingleEvent(of: .value) { (snapshot) in
        if let lockState = snapshot.value as? String, lockState == "true" {
            DispatchQueue.main.async {
                self.tableView.deselectRow(at: indexPath, animated: true)
                let alert = UIAlertController(title: "Locked", message: "That user's room is currently locked.", preferredStyle: .alert)
                alert.addAction(UIAlertAction(title: "Ok", style: .default, handler: nil))
                self.present(alert, animated: true, completion: nil)
            }
        } else {
            self.delegate?.didJoinFriend(uid: uid)

            self.dismiss(animated: true, completion: nil)
        }
    }
}