Smart-search for Parse Usernames in Swift not working

You will want to implement the UISearchResultsUpdating protocol to achieve this. It uses a UISearchController (introduced in iOS 8) which has to be added programmatically instead of through the storyboard, but don’t worry, it’s pretty straight-forward.

This should get the job done for you

Cheers,
Russell

class YourTableViewController: UITableViewController, UISearchBarDelegate, UISearchResultsUpdating {
    var searchUsers: [PFUser] = [PFUser]()
    var userSearchController = UISearchController()
    var searchActive: Bool = false

    // MARK: - Lifecycle

    override func viewDidLoad() {
        super.viewDidLoad()

        self.userSearchController = UISearchController(searchResultsController: nil)
        self.userSearchController.dimsBackgroundDuringPresentation = true

        // This is used for dynamic search results updating while the user types
        // Requires UISearchResultsUpdating delegate
        self.userSearchController.searchResultsUpdater = self

        // Configure the search controller's search bar
        self.userSearchController.searchBar.placeholder = "Search for a user"
        self.userSearchController.searchBar.sizeToFit()
        self.userSearchController.searchBar.delegate = self
        self.definesPresentationContext = true

        // Set the search controller to the header of the table
        self.tableView.tableHeaderView = self.userSearchController.searchBar
    }

    // MARK: - Parse Backend methods

    func loadSearchUsers(searchString: String) {
        var query = PFUser.query()

        // Filter by search string
        query.whereKey("username", containsString: searchString)

        self.searchActive = true
        query.findObjectsInBackgroundWithBlock { (objects: [AnyObject]?, error: NSError?) -> Void in

            if (error == nil) {
                self.searchUsers.removeAll(keepCapacity: false)
                self.searchUsers += objects as! [PFUser]
                self.tableView.reloadData()
            } else {
                // Log details of the failure
                println("search query error: \(error) \(error!.userInfo!)")
            }
            self.searchActive = false
        }
    }

    // MARK: - Search Bar Delegate Methods

    func searchBarSearchButtonClicked(searchBar: UISearchBar) {

        // Force search if user pushes button
        let searchString: String = searchBar.text.lowercaseString
        if (searchString != "") {
            loadSearchUsers(searchString)
        }
    }

    func searchBarCancelButtonClicked(searchBar: UISearchBar) {

        // Clear any search criteria
        searchBar.text = ""

        // Force reload of table data from normal data source
    }

    // MARK: - UISearchResultsUpdating Methods

    // This function is used along with UISearchResultsUpdating for dynamic search results processing
    // Called anytime the search bar text is changed
    func updateSearchResultsForSearchController(searchController: UISearchController) {

        let searchString: String = searchController.searchBar.text.lowercaseString
        if (searchString != "" && !self.searchActive) {
            loadSearchUsers(searchString)
        }
    }

    // MARK: - Table view data source

    override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
        return 1
    }

    override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        if (self.userSearchController.active) {
            return self.searchUsers.count
        } else {
            // return whatever your normal data source is
        }
    }

    override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
        var cell = tableView.dequeueReusableCellWithIdentifier("userCell") as! UserCell

        if (self.userSearchController.active && self.searchUsers.count > indexPath.row) {
            // bind data to the search results cell
        } else {
            // bind data from your normal data source
        }

        return cell
    }

    // MARK: - UITableViewDelegate

    override func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
        tableView.deselectRowAtIndexPath(indexPath, animated: true)

        if (self.userSearchController.active && self.searchUsers.count > 0) {
            // Segue or whatever you want
        } else {
            // normal data source selection
        }
    }
}