Using MKLocalSearch CompletionHandler correctly - ios

Question

I am using mapkit to make an app that helps users find nearby restaurants (among other things) that appeal to them and am trying to utilize a MKLocalSearch. I have declared myMapItems, which is an array of MKMapItem, and am trying to set it equal to the results of my MKLocalSearch. When printing the results of my MKLocalSearch, I am provided with all ten MKMapItems, but when setting the myMapItems array equal to the results, the console is telling me that myMapItems is nil. So:
var myMapItems: [MKMapItem]?
and then later, after defining "region" as an MKCoordinateRegion
let request = MKLocalSearchRequest()
request.naturalLanguageQuery = "Restaurants"
request.region = region!
let search = MKLocalSearch(request: request)
search.start { (response, error) in
print(response?.mapItems)
self.myMapItems = response?.mapItems
}
So when I press the button that runs this code, the console prints response.mapItems, but fails to set my mapItems declared earlier equal to the search's results.
More detailed code:
import UIKit
import MapKit
class MapViewController: UIViewController, CLLocationManagerDelegate {
#IBOutlet weak var mapView: MKMapView!
let locationManager = CLLocationManager()
#IBOutlet weak var slider: UISlider!
#IBAction func searchButtonPressed(_ sender: Any) {
search()
print(self.mapItems)
}
var mapItems: [MKMapItem] = []
func search() {
var region: MKCoordinateRegion?
let userLocation = CLLocation(latitude: (locationManager.location?.coordinate.latitude)!, longitude: (locationManager.location?.coordinate.longitude)!)
//Function for translating a CLLocationCoordinate2D by x meters
func locationWithBearing(bearing:Double, distanceMeters:Double, origin:CLLocationCoordinate2D) -> CLLocationCoordinate2D {
let distRadians = distanceMeters / (6372797.6)
let rbearing = bearing * Double.pi / 180.0
let lat1 = origin.latitude * Double.pi / 180
let lon1 = origin.longitude * Double.pi / 180
let lat2 = asin(sin(lat1) * cos(distRadians) + cos(lat1) * sin(distRadians) * cos(rbearing))
let lon2 = lon1 + atan2(sin(rbearing) * sin(distRadians) * cos(lat1), cos(distRadians) - sin(lat1) * sin(lat2))
return CLLocationCoordinate2D(latitude: lat2 * 180 / Double.pi, longitude: lon2 * 180 / Double.pi)
}
//Function for generating the search region within user's specified radius
func generateRandomSearchRegionWithinSpecifiedRadius() {
//Get user location
let userCurrentLocation = CLLocationCoordinate2DMake(userLocation.coordinate.latitude, userLocation.coordinate.longitude)
//Set randomLocationWithinSearchRadius to the user's current location translated in a randomly selected direction by a distance within x miles as specified by the user's slider
let randomLocationWithinSearchRadius = locationWithBearing(bearing: Double(arc4random_uniform(360)), distanceMeters: Double(arc4random_uniform(UInt32(slider.value * 1609.34))), origin: userCurrentLocation)
//Set region to an MKCoordinateRegion with this new CLLocationCoordinate2D as the center, searching within 3 miles
region = MKCoordinateRegionMakeWithDistance(randomLocationWithinSearchRadius, 4828.03, 4828.03)
print("\nRegion:\n Lat: \(region?.center.latitude ?? 0)\n Long: \(region?.center.longitude ?? 0)\n Radius: \(round((region?.span.latitudeDelta)! * 69))")
}
//Generate the random searching region within specified radius
generateRandomSearchRegionWithinSpecifiedRadius()
//Find distance between userLocation and our generated search location
let distanceBetweenLocations = CLLocation(latitude: (region?.center.latitude)!, longitude: (region?.center.longitude)!).distance(from: CLLocation(latitude: (userLocation.coordinate.latitude), longitude: (userLocation.coordinate.longitude)))
//Compare distance between locations with that requested by user's slider
print("\n Distance between locations: \(distanceBetweenLocations / 1609.34)\n Slider value: \(slider.value)\n\n\n")
//If the function generates a location whose distance from the user is further than that requested by the slider, the function will repeat
while distanceBetweenLocations > Double((slider.value) * 1609.34) {
generateRandomSearchRegionWithinSpecifiedRadius()
}
let request = MKLocalSearchRequest()
request.naturalLanguageQuery = "Restaurants"
request.region = region!
let search = MKLocalSearch(request: request)
search.start { (response, error) in
//print(response?.mapItems)
for item in (response?.mapItems)! {
self.mapItems.append(item)
}
}
}
The entire class should anybody need it:
import UIKit
import MapKit
class MapViewController: UIViewController, CLLocationManagerDelegate {
#IBOutlet weak var mapView: MKMapView!
let locationManager = CLLocationManager()
#IBOutlet weak var pickerTextField: UITextField!
let actions = ["A place to eat", "Something fun to do", "A park", "A club or bar"]
#IBOutlet weak var slider: UISlider!
#IBOutlet weak var distanceLabel: UILabel!
#IBOutlet weak var searchButton: UIButton!
override func viewDidLoad() {
super.viewDidLoad()
pickerTextField.loadDropdownData(data: actions)
// Do any additional setup after loading the view, typically from a nib.
// Core Location Manager asks for GPS location
locationManager.delegate = self
locationManager.desiredAccuracy = kCLLocationAccuracyBest
locationManager.requestWhenInUseAuthorization()
locationManager.startMonitoringSignificantLocationChanges()
// Check if the user allowed authorization
if (CLLocationManager.authorizationStatus() == CLAuthorizationStatus.authorizedWhenInUse ||
CLLocationManager.authorizationStatus() == CLAuthorizationStatus.authorizedAlways)
{
// set initial location as user's location
let initialLocation = CLLocation(latitude: (locationManager.location?.coordinate.latitude)!, longitude: (locationManager.location?.coordinate.longitude)!)
centerMapOnLocation(location: initialLocation, regionRadius: 1000)
print("Latitude: \(locationManager.location?.coordinate.latitude), Longitude: \(locationManager.location?.coordinate.longitude)")
} else {
print("Failed")
}
let span : MKCoordinateSpan = MKCoordinateSpanMake(0.1, 0.1)
let location : CLLocationCoordinate2D = CLLocationCoordinate2D(latitude: 38.645933, longitude: -90.503613)
let pin = PinAnnotation(title: "Gander", subtitle: "You can get food here", coordinate: location)
mapView.addAnnotation(pin)
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
func centerMapOnLocation(location: CLLocation, regionRadius: Double) {
let regionRadius = CLLocationDistance(regionRadius)
let coordinateRegion = MKCoordinateRegionMakeWithDistance(location.coordinate,
regionRadius, regionRadius)
mapView.setRegion(coordinateRegion, animated: true)
}
#IBAction func sliderAdjusted(_ sender: Any) {
var int = Int(slider.value)
distanceLabel.text = "\(int) miles"
}
#IBAction func searchButtonPressed(_ sender: Any) {
search()
print(self.mapItems)
//chooseRandomSearchResult(results: self.mapItems!)
}
var mapItems: [MKMapItem] = []
func search() {
var region: MKCoordinateRegion?
let userLocation = CLLocation(latitude: (locationManager.location?.coordinate.latitude)!, longitude: (locationManager.location?.coordinate.longitude)!)
//Function for translating a CLLocationCoordinate2D by x meters
func locationWithBearing(bearing:Double, distanceMeters:Double, origin:CLLocationCoordinate2D) -> CLLocationCoordinate2D {
let distRadians = distanceMeters / (6372797.6)
let rbearing = bearing * Double.pi / 180.0
let lat1 = origin.latitude * Double.pi / 180
let lon1 = origin.longitude * Double.pi / 180
let lat2 = asin(sin(lat1) * cos(distRadians) + cos(lat1) * sin(distRadians) * cos(rbearing))
let lon2 = lon1 + atan2(sin(rbearing) * sin(distRadians) * cos(lat1), cos(distRadians) - sin(lat1) * sin(lat2))
return CLLocationCoordinate2D(latitude: lat2 * 180 / Double.pi, longitude: lon2 * 180 / Double.pi)
}
//Function for generating the search region within user's specified radius
func generateRandomSearchRegionWithinSpecifiedRadius() {
//Get user location
let userCurrentLocation = CLLocationCoordinate2DMake(userLocation.coordinate.latitude, userLocation.coordinate.longitude)
//Set randomLocationWithinSearchRadius to the user's current location translated in a randomly selected direction by a distance within x miles as specified by the user's slider
let randomLocationWithinSearchRadius = locationWithBearing(bearing: Double(arc4random_uniform(360)), distanceMeters: Double(arc4random_uniform(UInt32(slider.value * 1609.34))), origin: userCurrentLocation)
//Set region to an MKCoordinateRegion with this new CLLocationCoordinate2D as the center, searching within 3 miles
region = MKCoordinateRegionMakeWithDistance(randomLocationWithinSearchRadius, 4828.03, 4828.03)
print("\nRegion:\n Lat: \(region?.center.latitude ?? 0)\n Long: \(region?.center.longitude ?? 0)\n Radius: \(round((region?.span.latitudeDelta)! * 69))")
}
//Generate the random searching region within specified radius
generateRandomSearchRegionWithinSpecifiedRadius()
//Find distance between userLocation and our generated search location
let distanceBetweenLocations = CLLocation(latitude: (region?.center.latitude)!, longitude: (region?.center.longitude)!).distance(from: CLLocation(latitude: (userLocation.coordinate.latitude), longitude: (userLocation.coordinate.longitude)))
//Compare distance between locations with that requested by user's slider
print("\n Distance between locations: \(distanceBetweenLocations / 1609.34)\n Slider value: \(slider.value)\n\n\n")
//If the function generates a location whose distance from the user is further than that requested by the slider, the function will repeat
while distanceBetweenLocations > Double((slider.value) * 1609.34) {
generateRandomSearchRegionWithinSpecifiedRadius()
}
let request = MKLocalSearchRequest()
request.naturalLanguageQuery = "Restaurants"
request.region = region!
let search = MKLocalSearch(request: request)
search.start { (response, error) in
//print(response?.mapItems)
for item in (response?.mapItems)! {
self.mapItems.append(item)
}
}
func chooseRandomSearchResult(results: [MKMapItem]) -> MKMapItem {
let numberOfItems = results.count
let randomNumber = Int(arc4random_uniform(UInt32(numberOfItems)))
return results[randomNumber]
}
}

Answer 1

The problem would be that search.start is ASYNCHRONOUS, it will start the request and return before results are done. Assume you need to work in completion handler.
Replace:
#IBAction func searchButtonPressed(_ sender: Any) {
search()
print(self.mapItems)
//chooseRandomSearchResult(results: self.mapItems!)
}
To: (Remove the usage of the results as they are not there yet, literally the search has been fired but has not returned)
#IBAction func searchButtonPressed(_ sender: Any) {
search()
}
AND do the actual work in the callback:
//Still inside search()
search.start { (response, error) in
//Executed after search() has already returned
print(response?.mapItems)
self.mapItems = response?.mapItems
chooseRandomSearchResult(results: self.mapItems!)
}
//Still inside search()
As you can see the code marked:
//Executed after search() has already returned
ALWAYS executes after //Still inside search()
even if it is before it in the function
(As of iOS 11.x, the documentation guarantees the completion handler for MKLocalSearch.start will be on the main thread)