UserSearchViewController.swift

func searchBar(_ searchBar: UISearchBar, textDidChange searchText: String) {
   resultsArray.removeAll()
   tableView.reloadData()
}


func searchBarSearchButtonClicked(_ searchBar: UISearchBar) {
   if let searchText = searchBar.text?.lowercased(), searchText != "" {
       resultsArray.removeAll()
       queryText(searchText, inField: "username")
   } else {
       let alert = UIAlertController(title: "Error", message: "Please enter a username.", preferredStyle: .alert)
       alert.addAction(UIAlertAction(title: "Ok", style: .default, handler: nil))
       present(alert, animated: true, completion: nil)
   }
}


func queryText(_ text: String, inField child: String) {
   userRef.queryOrdered(byChild: child)
       .queryStarting(atValue: text)
       .queryEnding(atValue: text+"\u{f8ff}")
       .observeSingleEvent(of: .value) { [weak self] (snapshot) in
           for case let item as DataSnapshot in snapshot.children {
               //Don't show the current user in search results
               if self?.currentUser?.uid == item.key {
                   continue
               }


               if var itemData = item.value as? [String:String] {
                   itemData["uid"] = item.key
                   self?.resultsArray.append(itemData)
               }
           }
           self?.tableView.reloadData()
   }
}