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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]
}

}

David Chopin
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  • At which line are you printing out on the console? – Mitchell Currie Feb 08 '18 at 02:07
  • @MitchellCurrie within search.start, which gets called in a function when I press a button. I also have it set self.myMapItems to the same results being printed, but after doing so I have it print myMapItems and the console is saying its nil. Also the application crashes anytime I try to use the contents of myMapItems because it is set to nil. – David Chopin Feb 08 '18 at 02:11
  • Can you post more code, including the class and any delegate methods implemented – Mitchell Currie Feb 08 '18 at 02:13
  • @MitchellCurrie I added most of the class, cutting out most of the material I deemed irrelevant to the question. The search() function is called when my UIButton is pressed, and most of the code at the beginning of search() is just generating "region" (which is used in the search request) via the variables given by the user. – David Chopin Feb 08 '18 at 02:21
  • The weird thing is you are saying it crashes when you try to use mapItems, however it is an optional which I do not see you force unwrap anywhere. A safer option REGARDLESS, would be to use an EMPTY array at all times. – Mitchell Currie Feb 08 '18 at 02:26
  • Also, the printing of self.mapItems in your searchPressed routine should fail whilst the print in search.start { (response, error) should succeed.. as far as I can tell, search.start is asynchronous, so the items will be nil after search() is invoked. Try adding chooseRandomSearchResult(results: self.mapItems!) after self.mapItems = response?.mapItems (possibly adding dispatch main) – Mitchell Currie Feb 08 '18 at 02:27
  • @MitchellCurrie I updated mapItems to: "var mapItems: [MKMapItem] = []" and changed the search request to say "let search = MKLocalSearch(request: request) search.start { (response, error) in //print(response?.mapItems) for item in (response?.mapItems)! { self.mapItems.append(item) } }"...now it just prints an empty array instead of nil. I'll edit my code in original post to reflect this. – David Chopin Feb 08 '18 at 02:30
  • See answer as its more organised. Problem appears to be the classic asynchronous return – Mitchell Currie Feb 08 '18 at 02:31

1 Answers1

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)

Mitchell Currie
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