Add Amazon Location tracking to your application

Add the TrackingBottomView.swift file in your project. Which has a button that starts and stops tracking user locations and shows tracking points on the map.

import SwiftUI

struct TrackingBottomView: View {
    @ObservedObject var trackingViewModel: TrackingViewModel
    var body: some View {
           Button(action: {
               Task {
                   if(trackingViewModel.trackingButtonText == NSLocalizedString("StartTrackingLabel", comment: "")) {
                       trackingViewModel.startTracking()
                   } else {
                       trackingViewModel.stopTracking()
                   }
               }
           }) {
               HStack {
                   Spacer()
                   Text("Tracking")
                       .foregroundColor(trackingViewModel.trackingButtonColor)
                       .background(.white)
                       .cornerRadius(15.0)
                   
                   Image(systemName: trackingViewModel.trackingButtonIcon)
                       .resizable()
                       .frame(width: 24, height: 24)
                       .padding(5)
                       .background(.white)
                       .foregroundColor(trackingViewModel.trackingButtonColor)

               }
           }
           .accessibility(identifier: "TrackingButton")
           .background(.white)
           .clipShape(RoundedRectangle(cornerRadius: 8))
           .padding(.trailing, 10)
           .padding(.bottom, 40)
           .frame(width: 130, alignment: .trailing)
           .shadow(color: Color.black.opacity(0.3), radius: 3, x: 0, y: 2)
       }
}

Update TrackingView.swift file with the following code

import SwiftUI

struct TrackingView: View {
    @ObservedObject var trackingViewModel: TrackingViewModel
    var body: some View {
        ZStack(alignment: .bottom) {
            if trackingViewModel.mapSigningIntialised {
                MapView(trackingViewModel: trackingViewModel)
                VStack {
                    UserLocationView(trackingViewModel: trackingViewModel)
                    CenterAddressView(trackingViewModel: trackingViewModel)
                    TrackingBottomView(trackingViewModel: trackingViewModel)
                }
            }
            else {
                Text("Loading...") 
            }
        }
        .onAppear() {
            if !trackingViewModel.identityPoolId.isEmpty {
                Task {
                    do {
                        try await trackingViewModel.authWithCognito(identityPoolId: trackingViewModel.identityPoolId)
                    }
                    catch {
                        print(error)
                    }
                }
            }
        }
    }
}

Add the following code in TrackingViewModel.swift file. These functions are responsible for start and stop tracking. It will also show an error alert if user location permission is denied.

To implement foreground tracking copy paste the following code example:

func showLocationDeniedRationale() {
        alertTitle = NSLocalizedString("locationManagerAlertTitle", comment: "")
        alertMessage = NSLocalizedString("locationManagerAlertText", comment: "")
        showAlert = true
    }
    
    // Required in info.plist: Privacy - Location When In Use Usage Description
    func startTracking() {
        do {
            print("Tracking Started...")
            if(client == nil) {
                initializeClient()
            }
            try client.startTracking()
            DispatchQueue.main.async { [self] in
                self.trackingButtonText = NSLocalizedString("StopTrackingLabel", comment: "")
                self.trackingButtonColor = .red
                self.trackingButtonIcon = "pause.circle"
                trackingActive = true
            }
        } catch TrackingLocationError.permissionDenied {
            showLocationDeniedRationale()
        } catch {
            print("error in tracking")
        }
    }
    
    func stopTracking() {
        print("Tracking Stopped...")
        client.stopTracking()
        trackingButtonText = NSLocalizedString("StartTrackingLabel", comment: "")
        trackingButtonColor = .blue
        trackingButtonIcon = "play.circle"
        trackingActive = false
    }

To get the locations from the user's device, you need to provide the start and end date and time. A single call returns a maximum of 100 tracking locations, but if there are more than 100 tracking locations, it will return a `nextToken` value. You will need to call subsequent `getTrackerDeviceLocation` calls with `nextToken` to load more tracking points for the given start and end time.

 func getTrackingPoints(nextToken: String? = nil) async throws {
        guard trackingActive else {
            return
        }
        // Initialize startTime to 24 hours ago from the current date and time.
        let startTime: Date = Date().addingTimeInterval(-86400)
        var endTime: Date = Date()
        if lastGetTrackingTime != nil {
            endTime = lastGetTrackingTime!
        }
        let result = try await client?.getTrackerDeviceLocation(nextToken: nextToken, startTime: startTime, endTime: endTime)
        if let trackingData = result {
            
            lastGetTrackingTime = Date()
            let devicePositions = trackingData.devicePositions

            let positions = devicePositions!.sorted { (pos1: LocationClientTypes.DevicePosition, pos2: LocationClientTypes.DevicePosition) -> Bool in
                guard let date1 = pos1.sampleTime,
                      let date2 = pos2.sampleTime else {
                    return false
                }
                return date1 < date2
            }

            let trackingPoints = positions.compactMap { position -> CLLocationCoordinate2D? in
                guard let latitude = position.position!.last, let longitude = position.position!.first else {
                    return nil
                }
                return CLLocationCoordinate2D(latitude: latitude, longitude: longitude)
            }
            DispatchQueue.main.async {
                self.mapViewDelegate!.drawTrackingPoints( trackingPoints: trackingPoints)
            }
            if let nextToken = trackingData.nextToken {
                try await getTrackingPoints(nextToken: nextToken)
            }
        }
    }

Now replace the code in the MapView.swift file with the following code:

import SwiftUI
import MapLibre

struct MapView: UIViewRepresentable {
    var onMapViewAvailable: ((MLNMapView) -> Void)?
    var mlnMapView: MLNMapView?
    var trackingViewModel: TrackingViewModel
    
    func makeCoordinator() -> MapView.Coordinator {
        return Coordinator(self, trackingViewModel: trackingViewModel)
    }
    
    func makeUIView(context: Context) -> MLNMapView {
        let styleURL = URL(string: "https://maps.geo.\(trackingViewModel.region).amazonaws.com/maps/v0/maps/\(trackingViewModel.mapName)/style-descriptor")
        let mapView = MLNMapView(frame: .zero, styleURL: styleURL)
        mapView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        mapView.setZoomLevel(15, animated: true)
        mapView.showsUserLocation = true
        mapView.userTrackingMode = .follow
        context.coordinator.mlnMapView = mapView
        mapView.delegate = context.coordinator

        mapView.logoView.isHidden = true
        context.coordinator.addCenterMarker()
        
        onMapViewAvailable?(mapView)
        trackingViewModel.mlnMapView = mapView
        return mapView
    }
    
    func updateUIView(_ uiView: MLNMapView, context: Context) {
    }
    
    class Coordinator: NSObject, MLNMapViewDelegate, MapViewDelegate {
        var control: MapView
        var mlnMapView: MLNMapView?
        var trackingViewModel: TrackingViewModel
        var centerMarker: MLNPointAnnotation?
        
        public init(_ control: MapView, trackingViewModel: TrackingViewModel) {
            self.control = control
            self.trackingViewModel = trackingViewModel
            super.init()
            self.trackingViewModel.mapViewDelegate = self
        }

        func mapViewDidFinishRenderingMap(_ mapView: MLNMapView, fullyRendered: Bool) {
            if(fullyRendered) {
                mapView.accessibilityIdentifier = "MapView"
                mapView.isAccessibilityElement = false
            }
        }
        
        func addCenterMarker() {
            guard let mlnMapView = mlnMapView else {
                return
            }

            let centerCoordinate = mlnMapView.centerCoordinate
            let marker = MLNPointAnnotation()
            marker.coordinate = centerCoordinate
            marker.accessibilityLabel = "CenterMarker"
            mlnMapView.addAnnotation(marker)
            centerMarker = marker

            trackingViewModel.reverseGeocodeCenter(centerCoordinate: centerCoordinate, marker: marker)
        }
        
        func mapView(_ mapView: MLNMapView, regionDidChangeAnimated animated: Bool) {
            if let marker = centerMarker {
                DispatchQueue.main.asyncAfter(deadline: .now() + 1.0) {
                    mapView.deselectAnnotation(marker, animated: false)
                    marker.coordinate = mapView.centerCoordinate
                    let centerCoordinate = mapView.centerCoordinate
                    self.trackingViewModel.reverseGeocodeCenter(centerCoordinate: centerCoordinate, marker: marker)
                }
            }
        }
        
        func mapView(_ mapView: MLNMapView, viewFor annotation: MLNAnnotation) -> MLNAnnotationView? {
            guard let pointAnnotation = annotation as? MLNPointAnnotation else {
                return nil
            }

            let reuseIdentifier: String
            var color: UIColor = .black
            if pointAnnotation.accessibilityLabel == "Tracking" {
                reuseIdentifier = "TrackingAnnotation"
                color = UIColor(red: 0.00784313725, green: 0.50588235294, blue: 0.58039215686, alpha: 1)
            } else if pointAnnotation.accessibilityLabel == "LocationChange" {
                reuseIdentifier = "LocationChange"
                color = .gray
            } else {
                reuseIdentifier = "DefaultAnnotationView"
            }

            var annotationView = mapView.dequeueReusableAnnotationView(withIdentifier: reuseIdentifier)

            if annotationView == nil {
                if reuseIdentifier != "DefaultAnnotationView" {
                    annotationView = MLNAnnotationView(annotation: annotation, reuseIdentifier: reuseIdentifier)
                    //If point annotation is an uploaded Tracking point the radius is 20 and color is blue, otherwise radius is 10 and color is gray
                    let radius = pointAnnotation.accessibilityLabel == "Tracking" ? 20:10
                    annotationView?.frame = CGRect(x: 0, y: 0, width: radius, height: radius)
                    annotationView?.backgroundColor = color
                    annotationView?.layer.cornerRadius = 10
                    
                    if pointAnnotation.accessibilityLabel == "Tracking" {
                        annotationView?.layer.borderColor = UIColor.white.cgColor
                        annotationView?.layer.borderWidth = 2.0
                        annotationView?.layer.shadowColor = UIColor.black.cgColor
                        annotationView?.layer.shadowOffset = CGSize(width: 0, height: 2)
                        annotationView?.layer.shadowRadius = 3
                        annotationView?.layer.shadowOpacity = 0.2
                        annotationView?.clipsToBounds = false
                    }
                }
                else {
                    return nil
                }
            }

            return annotationView
        }
        
        func mapView(_ mapView: MLNMapView, didUpdate userLocation: MLNUserLocation?) {
            if (userLocation?.location) != nil {
                if trackingViewModel.trackingActive {
                    let point = MLNPointAnnotation()
                    point.coordinate = (userLocation?.location!.coordinate)!
                    point.accessibilityLabel = "LocationChange"
                    mapView.addAnnotation(point)
                    Task {
                        do {
                            try await trackingViewModel.getTrackingPoints()
                        }
                        catch {
                            print(error)
                        }
                    }
                }
            }
        }
        
        func checkIfTrackingAnnotationExists(on mapView: MLNMapView, at coordinates: CLLocationCoordinate2D) -> Bool {
            let existingAnnotation = mapView.annotations?.first(where: { annotation in
                guard let annotation = annotation as? MLNPointAnnotation else { return false }
                return annotation.coordinate.latitude == coordinates.latitude &&
                annotation.coordinate.longitude == coordinates.longitude && annotation.accessibilityLabel == "Tracking" })
            return existingAnnotation != nil
        }
        
        public func drawTrackingPoints(trackingPoints: [CLLocationCoordinate2D]?) {
            guard let mapView = mlnMapView, let newTrackingPoints = trackingPoints, !newTrackingPoints.isEmpty else {
                return
            }

            let uniqueCoordinates = newTrackingPoints.filter { coordinate in
                !checkIfTrackingAnnotationExists(on: mapView, at: coordinate)
            }

            let points = uniqueCoordinates.map { coordinate -> MLNPointAnnotation in
                let point = MLNPointAnnotation()
                point.coordinate = coordinate
                point.accessibilityLabel = "Tracking"
                return point
            }
            mapView.addAnnotations(points)
        }
    }
}

protocol MapViewDelegate: AnyObject {
    func drawTrackingPoints(trackingPoints: [CLLocationCoordinate2D]?)
}

Create and add a new file called Localizable.xcstrings.

Right-click on the Localizable.xcstrings file and open it as Source Code.

Replace its content with the following:

{
  "sourceLanguage" : "en",
  "strings" : {
    "Cancel" : {
      "extractionState" : "manual",
      "localizations" : {
        "en" : {
          "stringUnit" : {
            "state" : "translated",
            "value" : "Cancel"
          }
        }
      }
    },
    "Error" : {
      "extractionState" : "manual",
      "localizations" : {
        "en" : {
          "stringUnit" : {
            "state" : "translated",
            "value" : "Error"
          }
        }
      }
    },
    "Loading..." : {

    },
    "locationManagerAlertText" : {
      "extractionState" : "manual",
      "localizations" : {
        "en" : {
          "stringUnit" : {
            "state" : "translated",
            "value" : "Allow \\\"Quick Start App\\\" to use your location"
          }
        }
      }
    },
    "locationManagerAlertTitle" : {
      "extractionState" : "manual",
      "localizations" : {
        "en" : {
          "stringUnit" : {
            "state" : "translated",
            "value" : "We need your location to detect your location in map"
          }
        }
      }
    },
    "NotAllFieldsAreConfigured" : {
      "extractionState" : "manual",
      "localizations" : {
        "en" : {
          "stringUnit" : {
            "state" : "translated",
            "value" : "Not all the fields are configured"
          }
        }
      }
    },
    "OK" : {
      "extractionState" : "manual",
      "localizations" : {
        "en" : {
          "stringUnit" : {
            "state" : "translated",
            "value" : "OK"
          }
        }
      }
    },
    "StartTrackingLabel" : {
      "localizations" : {
        "en" : {
          "stringUnit" : {
            "state" : "translated",
            "value" : "Start Tracking"
          }
        }
      }
    },
    "StopTrackingLabel" : {
      "localizations" : {
        "en" : {
          "stringUnit" : {
            "state" : "translated",
            "value" : "Stop Tracking"
          }
        }
      }
    },
    "Tracking" : {

    }
  },
  "version" : "1.0"
}

Save your files, and build and run your app to preview the functionality.

Allow the location permission and tap on the tracking button. The app will start uploading user locations and upload them to the Amazon Location tracker. It will also show user location changes, tracking points, and current address on the map.