Swift async await: how to use with several non async delegates? - swift

Question

I have created this simple example, it is a UITextField with an autocompletion ability, displaying a table view showing asynchronous data that evolves as the user types in the text field.
TextField
import UIKit
protocol TextFieldDelegate {
func autocompletedComponents(
_ textField: TextField,
_ components: #escaping ([String]) -> Void
)
}
class TextField: UITextField {
var components: [String] = []
var tableView = UITableView(frame: .zero)
var autocompletionDelegate: TextFieldDelegate? { didSet { setupUI() } }
// Actions
#objc private func didUpdateText() {
autocompletionDelegate?.autocompletedComponents(self) { [weak self] components in
guard let weakSelf = self else {
return
}
weakSelf.components = components
weakSelf.tableView.reloadData()
weakSelf.updateUI()
}
}
// Event
override func becomeFirstResponder() -> Bool {
tableView.isHidden = false
return super.becomeFirstResponder()
}
override func resignFirstResponder() -> Bool {
tableView.isHidden = true
return super.resignFirstResponder()
}
// Init
override init(frame: CGRect) {
super.init(frame: frame)
internalInit()
}
required init?(coder: NSCoder) {
super.init(coder: coder)
internalInit()
}
private func internalInit() {
addTarget(
self,
action: #selector(didUpdateText),
for: .editingChanged
)
}
// UI
private func setupUI() {
tableView.dataSource = self
tableView.delegate = self
tableView.showsVerticalScrollIndicator = false
tableView.removeFromSuperview()
superview?.addSubview(tableView)
}
private func updateUI() {
let tableViewHeight = Double(min(5, max(0, components.count))) * 44.0
tableView.frame = CGRect(
origin: CGPoint(
x: frame.origin.x,
y: frame.origin.y + frame.size.height
),
size: CGSize(
width: frame.size.width,
height: tableViewHeight
)
)
}
}
extension TextField: UITableViewDataSource, UITableViewDelegate {
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = UITableViewCell()
cell.textLabel?.text = components[indexPath.row]
return cell
}
func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
44.0
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
components.count
}
}
ViewController
import MapKit
import UIKit
class ViewController: UIViewController {
private var completion: (([MKLocalSearchCompletion]) -> Void)?
private var searchCompleter = MKLocalSearchCompleter()
#IBOutlet weak var textField: TextField!
override func viewDidLoad() {
super.viewDidLoad()
searchCompleter.delegate = self
textField.autocompletionDelegate = self
}
}
extension ViewController: TextFieldDelegate {
func autocompletedComponents(
_ textField: TextField,
_ components: #escaping ([String]) -> Void
) {
if completion == nil {
completion = { results in
components(results.map { $0.title })
}
}
searchCompleter.queryFragment = textField.text ?? ""
}
}
extension ViewController: MKLocalSearchCompleterDelegate {
func completerDidUpdateResults(_ completer: MKLocalSearchCompleter) {
completion?(completer.results)
}
}
In this example the view controller uses data from MapKit. Now I would like to get rid of the #escaping blocks and replace them with the new async/await syntax.
I have started rewriting the TextField code:
protocol TextFieldDelegate {
func autocompletedComponents(
_ textField: TextField
) async -> [String]
}
#objc private func didUpdateText() {
Task {
let autocompletedComponents = await autocompletionDelegate?.autocompletedComponents(self) ?? []
components = autocompletedComponents
tableView.reloadData()
updateUI()
}
}
However I am stuck in the ViewController, because I don't know what to do with the completion block I was using until now.
Thank you for your help

Answer 1

Here's an implementation using Combine's PassThroughSubject to send the array from MKLocalSearchCompleterDelegate to your autocompletedComponents function which then returns that array to be used in TextField
In ViewController:
class ViewController: UIViewController {
private var searchCompleter = MKLocalSearchCompleter()
var cancellables = Set<AnyCancellable>()
var publisher = PassthroughSubject<[String], Never>()
#IBOutlet weak var textField: TextField!
override func viewDidLoad() {
super.viewDidLoad()
searchCompleter.delegate = self
textField.autocompletionDelegate = self
}
}
extension ViewController: TextFieldDelegate {
func autocompletedComponents(
_ textField: TextField
) async -> [String] {
searchCompleter.queryFragment = textField.text ?? ""
return await withCheckedContinuation { continuation in
publisher
.sink { array in
continuation.resume(returning: array)
}.store(in: &cancellables)
}
}
}
extension ViewController: MKLocalSearchCompleterDelegate {
func completerDidUpdateResults(_ completer: MKLocalSearchCompleter) {
publisher.send(completer.results.map({$0.title}))
}
}
Or you could use your completion closure it would look like this:
func autocompletedComponents(
_ textField: TextField,
_ components: #escaping ([String]) -> Void
) {
return await withCheckedContinuation { continuation in
if completion == nil {
completion = { results in
continuation.resume(returning: results.map { $0.title })
}
}
searchCompleter.queryFragment = textField.text ?? ""
}
}