UserSearchViewController.swift

var resultsArray = [[String:String]]()

func searchBarSearchButtonClicked(_ searchBar: UISearchBar) {
    if let searchText = searchBar.text?.lowercased(), searchText != "" {
        resultsArray.removeAll()
        queryText(searchText, inField: "username")
        queryText(searchText, inField: "email")
    } 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)
        .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()
    }
}