Display Offline Maps

This section instructs how to register an offline-compatible map style, synchronize installed map data with the map engine, and switch to cache-only tile fetching when needed.

Create and register an offline-compatible style

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final class RegionalOfflineMapViewController: UIViewController {
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    private var mapView: NGLMapView!
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    private var connectivityObserver: NSObjectProtocol?
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    override func viewDidLoad() {
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        super.viewDidLoad()
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        mapView = NGLMapView(frame: view.bounds)
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        mapView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
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        view.addSubview(mapView)
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        applyStyle(named: "Bright")
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        observeConnectivity()
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        updateTileFetchMode()
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        NGLRegionalOffline.refreshEngineOnMapResume(completion: nil)
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    }
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    private func applyStyle(named name: String) {
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        guard let styleURL =
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            NGLRegionalOfflineStyleCatalog.uri(forName: name)
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        else {
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            return
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        }
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        mapView.styleURL = styleURL
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        NGLRegionalOfflineStyleCatalog.registerMapStyle(
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            forMapView: mapView,
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            styleURL: styleURL
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        )
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    }
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}

Read the available style names with:

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let styleNames = NGLRegionalOfflineStyleCatalog.styleNames

The current catalog includes Bright, Dark, Satellite, SatelliteStreet, NavDay, and NavNight. Register the new URL again whenever the application changes styles.

Synchronize the map when the page appears

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override func viewWillAppear(_ animated: Bool) {
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    super.viewWillAppear(animated)
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    updateTileFetchMode()
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    NGLRegionalOffline.onMapViewWillAppear()
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}

Refresh explicitly after returning from the download page:

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NGLRegionalOffline.refreshEngineOnMapResume { [weak self] in
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    // Installed database paths are now synchronized with the map engine.
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    self?.updateTileFetchMode()
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}

Switch to cache-only mode when offline

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private func observeConnectivity() {
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    connectivityObserver = NotificationCenter.default.addObserver(
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        forName: NGLRegionalOfflineNetworkConnectivityDidChangeNotification,
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        object: nil,
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        queue: .main
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    ) { [weak self] _ in
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        self?.updateTileFetchMode()
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    }
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}
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private func updateTileFetchMode() {
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    mapView.regionalOfflineTileFetchCacheOnly =
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        NGLRegionalOffline.isOfflineForRegionalFallback()
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}
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deinit {
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    if let connectivityObserver {
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        NotificationCenter.default.removeObserver(connectivityObserver)
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    }
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}

When regionalOfflineTileFetchCacheOnly is true, the map reads from shared preview resources and installed regional databases instead of requesting regional tiles online.

Focus the map on an installed region

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let focused = NGLRegionalOffline.focusPreviewRegion(
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    with: mapView,
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    regionId: regionId
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)
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if !focused {
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    // No usable database or bounds were found for this region.
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}