Generate offline map

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Take a web map offline.

Screenshot of generate offline map sample

Use case

Taking a web map offline allows users continued productivity when their network connectivity is poor or nonexistent. For example, by taking a map offline, a field worker inspecting utility lines in remote areas could still access a feature's location and attribute information.

How to use the sample

When the map loads, zoom to the extent you want to take offline. The red border shows the extent that will be downloaded. Tap the "Generate Offline Map" button to start the offline map job. The progress view will show the job's progress. When complete, the offline map will replace the online map in the map view.

How it works

Create a Map instance with a PortalItem.
Create an OfflineMapTask instance with the online map.
Create GenerateOfflineMapParameters parameters for the offline map task with OfflineMapTask.makeDefaultGenerateOfflineMapParameters(areaOfInterest:).
Create a GenerateOfflineMapJob with OfflineMapTask.makeGenerateOfflineMapJob(parameters:downloadDirectory:), using the parameters and specifying a download directory URL.
Start the job and await its output.
Get the offline map from the output when the job successfully finishes.

Relevant API

GenerateOfflineMapJob
GenerateOfflineMapParameters
GenerateOfflineMapResult
OfflineMapTask
OfflineMapTask.makeDefaultGenerateOfflineMapParameters(areaOfInterest:)
OfflineMapTask.makeGenerateOfflineMapJob(parameters:downloadDirectory:)
PortalItem

About the data

The map used in this sample shows the Naperville water network within Naperville, IL, USA, with cartography designed for web and mobile devices with offline support.

Additional information

The creation of the offline map can be fine-tuned using "Generate offline map (overrides)" sample, or by using "Generate offline map with local basemap" sample to achieve more customized results.

Sample Code

GenerateOfflineMapView.swift
Use dark colors for code blocksCopy
// Copyright 2022 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
//
//   https://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 ArcGIS
import SwiftUI

struct GenerateOfflineMapView: View {
    /// A Boolean value indicating whether the job is generating an offline map.
    @State private var isGeneratingOfflineMap = false

    /// A Boolean value indicating whether the job is cancelling.
    @State private var isCancellingJob = false

    /// The error shown in the error alert.
    @State private var error: Error?

    /// The view model for this sample.
    @StateObject private var model = Model()

    var body: some View {
        GeometryReader { geometry in
            MapViewReader { mapView in
                MapView(map: model.offlineMap ?? model.onlineMap)
                    .interactionModes(isGeneratingOfflineMap ? [] : [.pan, .zoom])
                    .errorAlert(presentingError: $error)
                    .task {
                        do {
                            try await model.initializeOfflineMapTask()
                        } catch {
                            self.error = error
                        }
                    }
                    .onDisappear {
                        Task { await model.cancelJob() }
                    }
                    .overlay {
                        Rectangle()
                            .stroke(.red, lineWidth: 2)
                            .padding(EdgeInsets(top: 20, leading: 20, bottom: 44, trailing: 20))
                            .opacity(model.offlineMap == nil ? 1 : 0)
                    }
                    .overlay {
                        if isGeneratingOfflineMap,
                           let progress = model.generateOfflineMapJob?.progress {
                            VStack(spacing: 16) {
                                ProgressView(progress)
                                    .progressViewStyle(.linear)
                                    .frame(maxWidth: 200)

                                Button("Cancel") {
                                    isCancellingJob = true
                                }
                                .disabled(isCancellingJob)
                                .task(id: isCancellingJob) {
                                    // Ensures cancelling the job is true.
                                    guard isCancellingJob else { return }
                                    // Cancels the job.
                                    await model.cancelJob()
                                    // Sets cancelling the job and generating an
                                    // offline map to false.
                                    isCancellingJob = false
                                    isGeneratingOfflineMap = false
                                }
                            }
                            .padding()
                            .background(.regularMaterial)
                            .clipShape(RoundedRectangle(cornerRadius: 15))
                            .shadow(radius: 3)
                        }
                    }
                    .overlay(alignment: .top) {
                        if model.offlineMap != nil {
                            Text("Offline map generated.")
                                .frame(maxWidth: .infinity, alignment: .center)
                                .padding(8)
                                .background(.thinMaterial, ignoresSafeAreaEdges: .horizontal)
                        }
                    }
                    .toolbar {
                        ToolbarItem(placement: .bottomBar) {
                            Button("Generate Offline Map") {
                                isGeneratingOfflineMap = true
                            }
                            .disabled(model.isGenerateDisabled || isGeneratingOfflineMap)
                            .task(id: isGeneratingOfflineMap) {
                                // Ensures generating an offline map is true.
                                guard isGeneratingOfflineMap else { return }

                                // Creates a rectangle from the area of interest.
                                let viewRect = geometry.frame(in: .local).inset(
                                    by: UIEdgeInsets(
                                        top: 20,
                                        left: geometry.safeAreaInsets.leading + 20,
                                        bottom: 44,
                                        right: -geometry.safeAreaInsets.trailing + 20
                                    )
                                )

                                // Creates an envelope from the rectangle.
                                guard let extent = mapView.envelope(fromViewRect: viewRect) else { return }

                                do {
                                    // Generates an offline map.
                                    try await model.generateOfflineMap(extent: extent)
                                } catch {
                                    self.error = error
                                }

                                // Sets generating an offline map to false.
                                isGeneratingOfflineMap = false
                            }
                        }
                    }
            }
        }
    }
}

private extension GenerateOfflineMapView {
    /// The model used to store the geo model and other expensive objects
    /// used in this view.
    @MainActor
    class Model: ObservableObject {
        /// The offline map that is generated.
        @Published private(set) var offlineMap: Map!

        /// A Boolean value indicating whether the generate button is disabled.
        @Published private(set) var isGenerateDisabled = true

        /// The generate offline map job.
        @Published private(set) var generateOfflineMapJob: GenerateOfflineMapJob!

        /// The offline map task.
        private var offlineMapTask: OfflineMapTask!

        /// A URL to a temporary directory where the offline map files are stored.
        private let temporaryDirectory = createTemporaryDirectory()

        /// A portal item displaying the Naperville, IL water network.
        private let napervillePortalItem = PortalItem(
            portal: .arcGISOnline(connection: .anonymous),
            id: PortalItem.ID("acc027394bc84c2fb04d1ed317aac674")!
        )

        /// The online map that is loaded from a portal item.
        let onlineMap: Map

        init() {
            // Initializes the online map.
            onlineMap = Map(item: napervillePortalItem)
            // Sets the min scale to avoid requesting a huge download.
            onlineMap.minScale = 1e4
        }

        deinit {
            // Removes the temporary directory.
            try? FileManager.default.removeItem(at: temporaryDirectory)
        }

        /// Initializes the offline map task.
        func initializeOfflineMapTask() async throws {
            // Waits for the online map to load.
            try await onlineMap.load()
            offlineMapTask = OfflineMapTask(onlineMap: onlineMap)
            isGenerateDisabled = false
        }

        /// Creates the generate offline map parameters.
        /// - Parameter areaOfInterest: The area of interest to create the parameters for.
        /// - Returns: A `GenerateOfflineMapParameters` if there are no errors.
        private func makeGenerateOfflineMapParameters(areaOfInterest: Envelope) async throws -> GenerateOfflineMapParameters {
            // Returns the default parameters for the offline map task.
            return try await offlineMapTask.makeDefaultGenerateOfflineMapParameters(areaOfInterest: areaOfInterest)
        }

        /// Generates the offline map.
        /// - Parameter extent: The area of interest's envelope to generate an offline map for.
        func generateOfflineMap(extent: Envelope) async throws {
            // Disables the generate offline map button.
            isGenerateDisabled = true

            // Creates the default parameters for the offline map task.
            let parameters = try await makeGenerateOfflineMapParameters(areaOfInterest: extent)

            // Creates the generate offline map job based on the parameters.
            generateOfflineMapJob = offlineMapTask.makeGenerateOfflineMapJob(
                parameters: parameters,
                downloadDirectory: temporaryDirectory
            )

            // Starts the job.
            generateOfflineMapJob.start()

            defer {
                generateOfflineMapJob = nil
                isGenerateDisabled = offlineMap != nil
            }

            // Awaits the output of the job.
            let output = try await generateOfflineMapJob.output
            // Sets the offline map to the output's offline map.
            offlineMap = output.offlineMap
            // Sets the initial viewpoint of the offline map.
            offlineMap.initialViewpoint = Viewpoint(boundingGeometry: extent.expanded(by: 0.8))
        }

        /// Cancels the generate offline map job.
        func cancelJob() async {
            // Cancels the generate offline map job.
            await generateOfflineMapJob?.cancel()
            generateOfflineMapJob = nil
        }

        /// Creates a temporary directory.
        private static func createTemporaryDirectory() -> URL {
            // swiftlint:disable:next force_try
            try! FileManager.default.url(
                for: .itemReplacementDirectory,
                in: .userDomainMask,
                appropriateFor: FileManager.default.temporaryDirectory,
                create: true
            )
        }
    }
}

private extension Envelope {
    /// Expands the envelope by a given factor.
    func expanded(by factor: Double) -> Envelope {
        let builder = EnvelopeBuilder(envelope: self)
        builder.expand(by: factor)
        return builder.toGeometry()
    }
}

#Preview {
    NavigationStack {
        GenerateOfflineMapView()
    }
}