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 {
        // Show an error
        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()
    }
}

func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return resultsArray.count
}

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: "userCell", for: indexPath)

    if let userCell = cell as? UserTableViewCell {
        let userData = resultsArray[indexPath.row]
        userCell.displayName.text = userData["displayname"]
    }

    return cell
}