Reverse geocode

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// Copyright 2016 Esri.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

import UIKit
import ArcGIS

class ReverseGeocodeViewController: UIViewController, AGSGeoViewTouchDelegate {
    @IBOutlet weak var mapView: AGSMapView!
    private var map: AGSMap!

    private var locatorTask: AGSLocatorTask!
    private var reverseGeocodeParameters: AGSReverseGeocodeParameters!
    private var graphicsOverlay = AGSGraphicsOverlay()
    private var cancelable: AGSCancelable!

    private let locatorURL = "https://geocode.arcgis.com/arcgis/rest/services/World/GeocodeServer"

    override func viewDidLoad() {
        super.viewDidLoad()

        // add the source code button item to the right of navigation bar
        (self.navigationItem.rightBarButtonItem as! SourceCodeBarButtonItem).filenames = ["ReverseGeocodeViewController"]

        // create an instance of a map with ESRI topographic basemap
        self.map = AGSMap(basemapStyle: .arcGISTopographic)

        self.mapView.map = self.map
        self.mapView.touchDelegate = self

        // add the graphics overlay
        self.mapView.graphicsOverlays.add(self.graphicsOverlay)

        // zoom to a specific extent
        self.mapView.setViewpoint(AGSViewpoint(center: AGSPoint(x: -117.195, y: 34.058, spatialReference: .wgs84()), scale: 5e4))

        // initialize locator task
        self.locatorTask = AGSLocatorTask(url: URL(string: self.locatorURL)!)

        // initialize parameters
        self.reverseGeocodeParameters = AGSReverseGeocodeParameters()
        self.reverseGeocodeParameters.maxResults = 1
    }

    private func reverseGeocode(_ point: AGSPoint) {
        // cancel previous request
        if self.cancelable != nil {
            self.cancelable.cancel()
        }

        // hide the callout
        self.mapView.callout.dismiss()

        // remove already existing graphics
        self.graphicsOverlay.graphics.removeAllObjects()

        // normalize point
        let normalizedPoint = AGSGeometryEngine.normalizeCentralMeridian(of: point) as! AGSPoint

        let graphic = self.graphicForPoint(normalizedPoint)
        self.graphicsOverlay.graphics.add(graphic)

        // reverse geocode
        self.cancelable = self.locatorTask.reverseGeocode(withLocation: normalizedPoint, parameters: self.reverseGeocodeParameters) { [weak self] (results: [AGSGeocodeResult]?, error: Error?) in
            if let error = error as NSError? {
                if error.code != NSUserCancelledError { // user canceled error
                    self?.presentAlert(error: error)
                }
            } else if let result = results?.first {
                graphic.attributes.addEntries(from: result.attributes!)
                self?.showCalloutForGraphic(graphic, tapLocation: normalizedPoint)
                return
            } else {
                self?.presentAlert(message: "No address found")
            }
            self?.graphicsOverlay.graphics.remove(graphic)
        }
    }

    // method returns a graphic object for the specified point and attributes
    private func graphicForPoint(_ point: AGSPoint) -> AGSGraphic {
        let markerImage = UIImage(named: "RedMarker")!
        let symbol = AGSPictureMarkerSymbol(image: markerImage)
        symbol.leaderOffsetY = markerImage.size.height / 2
        symbol.offsetY = markerImage.size.height / 2
        let graphic = AGSGraphic(geometry: point, symbol: symbol, attributes: [String: AnyObject]())
        return graphic
    }

    // method to show callout for the graphic
    // it gets the attributes from the graphic and populates the title
    // and detail for the callout
    private func showCalloutForGraphic(_ graphic: AGSGraphic, tapLocation: AGSPoint) {
        let cityString = graphic.attributes["City"] as? String ?? ""
        let addressString = graphic.attributes["Address"] as? String ?? ""
        let stateString = graphic.attributes["State"] as? String ?? ""
        self.mapView.callout.title = addressString
        self.mapView.callout.detail = "\(cityString) \(stateString)"
        self.mapView.callout.isAccessoryButtonHidden = true
        self.mapView.callout.show(for: graphic, tapLocation: tapLocation, animated: true)
    }

    // MARK: - AGSGeoViewTouchDelegate

    func geoView(_ geoView: AGSGeoView, didTapAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
        self.reverseGeocode(mapPoint)
    }
}