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JobTCancel Method

Cancels execution of the job

Namespace:  Esri.ArcGISRuntime.Tasks
Assembly:  Esri.ArcGISRuntime (in Esri.ArcGISRuntime.dll) Version: 100.9.0.0
Syntax
C#
public bool Cancel()

Return Value

Type: Boolean
false if already canceled or cannot be cannot be canceled; otherwise, true.
Remarks
This cancels the job, which sets Status to failed. Server jobs (i.e. execution on the server) corresponding to the job instance cannot be canceled and are abandoned.
Examples

Android

Example Name: GenerateOfflineMap

Take a web map offline.

Code example screen shot.

C#
// Copyright 2018 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.

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Threading.Tasks;
using Android.App;
using Android.OS;
using Android.Widget;
using Esri.ArcGISRuntime.Geometry;
using Esri.ArcGISRuntime.Mapping;
using Esri.ArcGISRuntime.Portal;
using Esri.ArcGISRuntime.Security;
using Esri.ArcGISRuntime.Symbology;
using Esri.ArcGISRuntime.Tasks;
using Esri.ArcGISRuntime.Tasks.Offline;
using Esri.ArcGISRuntime.UI;
using Esri.ArcGISRuntime.UI.Controls;
using Xamarin.Auth;

namespace ArcGISRuntime.Samples.GenerateOfflineMap
{
    [Activity (ConfigurationChanges=Android.Content.PM.ConfigChanges.Orientation | Android.Content.PM.ConfigChanges.ScreenSize)]
    [ArcGISRuntime.Samples.Shared.Attributes.Sample(
        name: "Generate offline map",
        category: "Map",
        description: "Take a web map offline.",
        instructions: "When the app starts, you will be prompted to sign in using a free ArcGIS Online account. Once the map loads, zoom to the extent you want to take offline. The red border shows the extent that will be downloaded. Tap the \"Take Map Offline\" button to start the offline map job. The progress bar will show the job's progress. When complete, the offline map will replace the online map in the map view.",
        tags: new[] { "download", "offline", "save", "web map" })]
    public class GenerateOfflineMap : Activity, IOAuthAuthorizeHandler
    {
        // Mapview.
        private MapView _mapView;

        // Generate Button.
        private Button _takeMapOfflineButton;

        // Progress indicator.
        private AlertDialog _alertDialog;
        private ProgressBar _progressIndicator;

        // The job to generate an offline map.
        private GenerateOfflineMapJob _generateOfflineMapJob;

        // The extent of the data to take offline.
        private Envelope _areaOfInterest = new Envelope(-88.1541, 41.7690, -88.1471, 41.7720, SpatialReferences.Wgs84);

        // The ID for a web map item hosted on the server (water network map of Naperville IL).
        private string WebMapId = "acc027394bc84c2fb04d1ed317aac674";

        protected override void OnCreate(Bundle bundle)
        {
            base.OnCreate(bundle);
            Title = "Generate offline map";

            // Create the UI, setup the control references and execute initialization.
            CreateLayout();
            Initialize();
        }

        private void CreateLayout()
        {
            // Create the layout.
            LinearLayout layout = new LinearLayout(this)
            {
                Orientation = Orientation.Vertical
            };

            // Add the generate button.
            _takeMapOfflineButton = new Button(this)
            {
                Text = "Take map offline"
            };
            _takeMapOfflineButton.Click += TakeMapOfflineButton_Click;
            layout.AddView(_takeMapOfflineButton);

            // Add the mapview.
            _mapView = new MapView(this);
            layout.AddView(_mapView);

            // Add the layout to the view.
            SetContentView(layout);

            // Create the progress dialog display.
            _progressIndicator = new ProgressBar(this);
            _progressIndicator.SetProgress(40, true);
            AlertDialog.Builder builder = new AlertDialog.Builder(this).SetView(_progressIndicator);
            builder.SetCancelable(true);
            builder.SetMessage("Generating offline map ...");
            _alertDialog = builder.Create();
            _alertDialog.SetButton("Cancel", (s, e) => 
            {
                _generateOfflineMapJob.Cancel();
            });
        }

        private async void Initialize()
        {
            try
            {
                // Call a function to set up the AuthenticationManager for OAuth.
                SetOAuthInfo();

                // Create the ArcGIS Online portal.
                ArcGISPortal portal = await ArcGISPortal.CreateAsync();

                // Get the Naperville water web map item using its ID.
                PortalItem webmapItem = await PortalItem.CreateAsync(portal, WebMapId);

                // Create a map from the web map item.
                Map onlineMap = new Map(webmapItem);

                // Display the map in the MapView.
                _mapView.Map = onlineMap;

                // Disable user interactions on the map (no panning or zooming from the initial extent).
                _mapView.InteractionOptions = new MapViewInteractionOptions
                {
                    IsEnabled = false
                };

                // Create a graphics overlay for the extent graphic and apply a renderer.
                SimpleLineSymbol aoiOutlineSymbol = new SimpleLineSymbol(SimpleLineSymbolStyle.Solid, System.Drawing.Color.Red, 3);
                GraphicsOverlay extentOverlay = new GraphicsOverlay
                {
                    Renderer = new SimpleRenderer(aoiOutlineSymbol)
                };
                _mapView.GraphicsOverlays.Add(extentOverlay);

                // Add a graphic to show the area of interest (extent) that will be taken offline.
                Graphic aoiGraphic = new Graphic(_areaOfInterest);
                extentOverlay.Graphics.Add(aoiGraphic);
            }
            catch (Exception ex)
            {
                // Show the exception message to the user.
                ShowStatusMessage(ex.Message);
            }
        }

        private async void TakeMapOfflineButton_Click(object sender, EventArgs e)
        {
            // Create a path for the output mobile map.
            string tempPath = $"{Path.GetTempPath()}";
            string[] outputFolders = Directory.GetDirectories(tempPath, "NapervilleWaterNetwork*");

            // Loop through the folder names and delete them.
            foreach (string dir in outputFolders)
            {
                try
                {
                    // Delete the folder.
                    Directory.Delete(dir, true);
                }
                catch (Exception)
                {
                    // Ignore exceptions (files might be locked, for example).
                }
            }

            // Create a new folder for the output mobile map.
            string packagePath = Path.Combine(tempPath, @"NapervilleWaterNetwork");
            int num = 1;
            while (Directory.Exists(packagePath))
            {
                packagePath = Path.Combine(tempPath, @"NapervilleWaterNetwork" + num.ToString());
                num++;
            }

            // Create the output directory.
            Directory.CreateDirectory(packagePath);

            try
            {
                // Show the progress dialog while the job is running.
                _alertDialog.Show();

                // Create an offline map task with the current (online) map.
                OfflineMapTask takeMapOfflineTask = await OfflineMapTask.CreateAsync(_mapView.Map);

                // Create the default parameters for the task, pass in the area of interest.
                GenerateOfflineMapParameters parameters = await takeMapOfflineTask.CreateDefaultGenerateOfflineMapParametersAsync(_areaOfInterest);

                // Create the job with the parameters and output location.
                _generateOfflineMapJob = takeMapOfflineTask.GenerateOfflineMap(parameters, packagePath);

                // Handle the progress changed event for the job.
                _generateOfflineMapJob.ProgressChanged += OfflineMapJob_ProgressChanged;

                // Await the job to generate geodatabases, export tile packages, and create the mobile map package.
                GenerateOfflineMapResult results = await _generateOfflineMapJob.GetResultAsync();

                // Check for job failure (writing the output was denied, e.g.).
                if (_generateOfflineMapJob.Status != JobStatus.Succeeded)
                {
                    // Report failure to the user.
                    ShowStatusMessage("Failed to take the map offline.");

                }

                // Check for errors with individual layers.
                if (results.LayerErrors.Any())
                {
                    // Build a string to show all layer errors.
                    System.Text.StringBuilder errorBuilder = new System.Text.StringBuilder();
                    foreach (KeyValuePair<Layer, Exception> layerError in results.LayerErrors)
                    {
                        errorBuilder.AppendLine(string.Format("{0} : {1}", layerError.Key.Id, layerError.Value.Message));
                    }

                    // Show layer errors.
                    ShowStatusMessage(errorBuilder.ToString());
                }

                // Display the offline map.
                _mapView.Map = results.OfflineMap;

                // Apply the original viewpoint for the offline map.
                _mapView.SetViewpoint(new Viewpoint(_areaOfInterest));

                // Enable map interaction so the user can explore the offline data.
                _mapView.InteractionOptions.IsEnabled = true;

                // Change the title and disable the "Take map offline" button.
                _takeMapOfflineButton.Text = "Map is offline";
                _takeMapOfflineButton.Enabled = false;
            }
            catch (TaskCanceledException)
            {
                // Generate offline map task was canceled.
                ShowStatusMessage("Taking map offline was canceled");
            }
            catch (Exception ex)
            {
                // Exception while taking the map offline.
                ShowStatusMessage(ex.Message);
            }
            finally
            {
                // Hide the loading overlay when the job is done.
                _alertDialog.Dismiss();
            }
        }

        private void ShowStatusMessage(string message)
        {
            // Display the message to the user.
            AlertDialog.Builder builder = new AlertDialog.Builder(this);
            builder.SetMessage(message).SetTitle("Alert").Show();
        }

        // Show changes in job progress.
        private void OfflineMapJob_ProgressChanged(object sender, EventArgs e)
        {
            // Get the job.
            GenerateOfflineMapJob job = sender as GenerateOfflineMapJob;

            // Dispatch to the UI thread.
            RunOnUiThread(() =>
            {
                // Show the percent complete and update the progress bar.
                string percentText = job.Progress > 0 ? job.Progress.ToString() + " %" : string.Empty;
                _progressIndicator.Progress = job.Progress;
                _alertDialog.SetMessage($"Taking map offline ({percentText}) ...");
            });
        }

        #region Authentication
        // Constants for OAuth-related values.
        // - The URL of the portal to authenticate with (ArcGIS Online).
        private const string ServerUrl = "https://www.arcgis.com/sharing/rest";
        // - The Client ID for an app registered with the server (the ID below is for a public app created by the ArcGIS Runtime team).
        private const string AppClientId = @"lgAdHkYZYlwwfAhC";
        // - A URL for redirecting after a successful authorization (this must be a URL configured with the app).
        private const string OAuthRedirectUrl = @"my-ags-app://auth";

        private void SetOAuthInfo()
        {
            // Register the server information with the AuthenticationManager.
            ServerInfo serverInfo = new ServerInfo
            {
                ServerUri = new Uri(ServerUrl),
                TokenAuthenticationType = TokenAuthenticationType.OAuthImplicit,
                OAuthClientInfo = new OAuthClientInfo
                {
                    ClientId = AppClientId,
                    RedirectUri = new Uri(OAuthRedirectUrl)
                }
            };

            // Register this server with AuthenticationManager.
            AuthenticationManager.Current.RegisterServer(serverInfo);

            // Use a function in this class to challenge for credentials.
            AuthenticationManager.Current.ChallengeHandler = new ChallengeHandler(CreateCredentialAsync);

            // Set the OAuthAuthorizeHandler component (this class) for Android or iOS platforms.
            AuthenticationManager.Current.OAuthAuthorizeHandler = this;
        }

        // ChallengeHandler function that will be called whenever access to a secured resource is attempted.
        public async Task<Credential> CreateCredentialAsync(CredentialRequestInfo info)
        {
            Credential credential = null;

            try
            {
                // IOAuthAuthorizeHandler will challenge the user for OAuth credentials.
                credential = await AuthenticationManager.Current.GenerateCredentialAsync(info.ServiceUri);
            }
            catch (TaskCanceledException) { return credential; }
            catch (Exception)
            {
                // Exception will be reported in calling function.
                throw;
            }

            return credential;
        }

        #region IOAuthAuthorizationHandler implementation
        // Use a TaskCompletionSource to track the completion of the authorization.
        private TaskCompletionSource<IDictionary<string, string>> _taskCompletionSource;

        // IOAuthAuthorizeHandler.AuthorizeAsync implementation.
        public Task<IDictionary<string, string>> AuthorizeAsync(Uri serviceUri, Uri authorizeUri, Uri callbackUri)
        {
            // If the TaskCompletionSource is not null, authorization may already be in progress and should be canceled.
            if (_taskCompletionSource != null)
            {
                // Try to cancel any existing authentication task.
                _taskCompletionSource.TrySetCanceled();
            }

            // Create a task completion source.
            _taskCompletionSource = new TaskCompletionSource<IDictionary<string, string>>();

            // Get the current Android Activity.
            Activity activity = (Activity)this;

            // Create a new Xamarin.Auth.OAuth2Authenticator using the information passed in.
            OAuth2Authenticator authenticator = new OAuth2Authenticator(
                clientId: AppClientId,
                scope: "",
                authorizeUrl: authorizeUri,
                redirectUrl: callbackUri)
            {
                ShowErrors = false,
                // Allow the user to cancel the OAuth attempt.
                AllowCancel = true
            };

            // Define a handler for the OAuth2Authenticator.Completed event.
            authenticator.Completed += (sender, authArgs) =>
            {
                try
                {

                    // Check if the user is authenticated.
                    if (authArgs.IsAuthenticated)
                    {
                        // If authorization was successful, get the user's account.
                        Xamarin.Auth.Account authenticatedAccount = authArgs.Account;

                        // Set the result (Credential) for the TaskCompletionSource.
                        _taskCompletionSource.SetResult(authenticatedAccount.Properties);
                    }
                    else
                    {
                        throw new Exception("Unable to authenticate user.");
                    }
                }
                catch (Exception ex)
                {
                    // If authentication failed, set the exception on the TaskCompletionSource.
                    _taskCompletionSource.TrySetException(ex);

                    // Cancel authentication.
                    authenticator.OnCancelled();
                }
                finally
                {
                    // Dismiss the OAuth login.
                    activity.FinishActivity(99);
                }
            };

            // If an error was encountered when authenticating, set the exception on the TaskCompletionSource.
            authenticator.Error += (sndr, errArgs) =>
            {
                // If the user cancels, the Error event is raised but there is no exception ... best to check first.
                if (errArgs.Exception != null)
                {
                    _taskCompletionSource.TrySetException(errArgs.Exception);
                }
                else
                {
                    // Login canceled: dismiss the OAuth login.
                    if (_taskCompletionSource != null)
                    {
                        _taskCompletionSource.TrySetCanceled();
                        activity.FinishActivity(99);
                    }
                }

                // Cancel authentication.
                authenticator.OnCancelled();
            };

            // Present the OAuth UI so the user can enter user name and password.
            Android.Content.Intent intent = authenticator.GetUI(activity);
            activity.StartActivityForResult(intent, 99);

            // Return completion source task so the caller can await completion.
            return _taskCompletionSource.Task;
        }
        #endregion

        #endregion
    }
}
Examples

Xamarin Forms Android

Example Name: OfflineBasemapByReference

Use the `OfflineMapTask` to take a web map offline, but instead of downloading an online basemap, use one which is already on the device.

Code example screen shot.

C#
// Copyright 2019 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.

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Threading.Tasks;
using ArcGISRuntime.Samples.Managers;
using Esri.ArcGISRuntime.Geometry;
using Esri.ArcGISRuntime.Mapping;
using Esri.ArcGISRuntime.Symbology;
using Esri.ArcGISRuntime.Tasks;
using Esri.ArcGISRuntime.Tasks.Offline;
using Esri.ArcGISRuntime.UI;
using Esri.ArcGISRuntime.Portal;
using Esri.ArcGISRuntime.Security;
using Xamarin.Forms;
#if __IOS__
using Xamarin.Auth;
using UIKit;

#endif

#if __ANDROID__
using Android.App;
using Application = Xamarin.Forms.Application;
using Xamarin.Auth;
#endif

namespace ArcGISRuntimeXamarin.Samples.OfflineBasemapByReference
{
    [ArcGISRuntime.Samples.Shared.Attributes.Sample(
        name: "Generate offline map with local basemap",
        category: "Map",
        description: "Use the `OfflineMapTask` to take a web map offline, but instead of downloading an online basemap, use one which is already on the device.",
        instructions: "1. Use the button to start taking the map offline.",
        tags: new[] { "Offline" })]
    [ArcGISRuntime.Samples.Shared.Attributes.OfflineData("628e8e3521cf45e9a28a12fe10c02c4d")]
    public partial class OfflineBasemapByReference : ContentPage, IOAuthAuthorizeHandler
    {
        // The job to generate an offline map.
        private GenerateOfflineMapJob _generateOfflineMapJob;

        // The extent of the data to take offline.
        private readonly Envelope _areaOfInterest = new Envelope(-88.1541, 41.7690, -88.1471, 41.7720, SpatialReferences.Wgs84);

        // The ID for a web map item hosted on the server (water network map of Naperville IL).
        private const string WebMapId = "acc027394bc84c2fb04d1ed317aac674";

        public OfflineBasemapByReference()
        {
            InitializeComponent();
            Initialize();
        }

        private async Task ConfigureOfflineJobForBasemap(GenerateOfflineMapParameters parameters)
        {
            // Don't give the user a choice if there is no basemap specified.
            if (String.IsNullOrWhiteSpace(parameters.ReferenceBasemapFilename))
            {
                return;
            }

            // Get the path to the basemap directory.
            string basemapBasePath = DataManager.GetDataFolder("628e8e3521cf45e9a28a12fe10c02c4d");

            // Get the full path to the basemap by combining the name specified in the web map (ReferenceBasemapFilename)
            //  with the offline basemap directory.
            string basemapFullPath = Path.Combine(basemapBasePath, parameters.ReferenceBasemapFilename);

            // If the offline basemap doesn't exist, proceed without it.
            if (!File.Exists(basemapFullPath))
            {
                return;
            }

            // Wait for the user to choose whether to use the offline basemap.
            bool useBasemap = await Application.Current.MainPage.DisplayAlert("Basemap choice", "Use the offline basemap?", "Yes", "No");

            if (useBasemap)
            {
                // Configure the offline basemap if the user said yes.
                parameters.ReferenceBasemapDirectory = basemapBasePath;
            }
        }

        // Note: all code below (except call to ConfigureOfflineJobForBasemap) is identical to code in the Generate offline map sample.

        #region Generate offline map

        private async void Initialize()
        {
            try
            {
                // Call a function to set up the AuthenticationManager for OAuth.
                SetOAuthInfo();

                // Create the ArcGIS Online portal.
                ArcGISPortal portal = await ArcGISPortal.CreateAsync();

                // Get the Naperville water web map item using its ID.
                PortalItem webmapItem = await PortalItem.CreateAsync(portal, WebMapId);

                // Create a map from the web map item.
                Map onlineMap = new Map(webmapItem);

                // Display the map in the MapView.
                MyMapView.Map = onlineMap;

                // Disable user interactions on the map (no panning or zooming from the initial extent).
                MyMapView.InteractionOptions = new MapViewInteractionOptions
                {
                    IsEnabled = false
                };

                // Create a graphics overlay for the extent graphic and apply a renderer.
                SimpleLineSymbol aoiOutlineSymbol = new SimpleLineSymbol(SimpleLineSymbolStyle.Solid, System.Drawing.Color.Red, 3);
                GraphicsOverlay extentOverlay = new GraphicsOverlay
                {
                    Renderer = new SimpleRenderer(aoiOutlineSymbol)
                };
                MyMapView.GraphicsOverlays.Add(extentOverlay);

                // Add a graphic to show the area of interest (extent) that will be taken offline.
                Graphic aoiGraphic = new Graphic(_areaOfInterest);
                extentOverlay.Graphics.Add(aoiGraphic);

                // Hide the map loading progress indicator.
                LoadingIndicator.IsVisible = false;
            }
            catch (Exception ex)
            {
                await Application.Current.MainPage.DisplayAlert("Alert", ex.ToString(), "OK");
            }
        }

        private async void TakeMapOfflineButton_Click(object sender, EventArgs e)
        {
            // Clean up any previous outputs in the temp directory.
            string tempPath = $"{Path.GetTempPath()}";
            string[] outputFolders = Directory.GetDirectories(tempPath, "NapervilleWaterNetwork*");

            // Loop through the folder names and delete them.
            foreach (string dir in outputFolders)
            {
                try
                {
                    // Delete the folder.
                    Directory.Delete(dir, true);
                }
                catch (Exception)
                {
                    // Ignore exceptions (files might be locked, for example).
                }
            }

            // Create a new folder for the output mobile map.
            string packagePath = Path.Combine(tempPath, @"NapervilleWaterNetwork");
            int num = 1;
            while (Directory.Exists(packagePath))
            {
                packagePath = Path.Combine(tempPath, @"NapervilleWaterNetwork" + num.ToString());
                num++;
            }

            // Create the output directory.
            Directory.CreateDirectory(packagePath);

            try
            {
                // Show the progress indicator while the job is running.
                BusyIndicator.IsVisible = true;

                // Create an offline map task with the current (online) map.
                OfflineMapTask takeMapOfflineTask = await OfflineMapTask.CreateAsync(MyMapView.Map);

                // Create the default parameters for the task, pass in the area of interest.
                GenerateOfflineMapParameters parameters = await takeMapOfflineTask.CreateDefaultGenerateOfflineMapParametersAsync(_areaOfInterest);

                // Configure basemap settings for the job.
                await ConfigureOfflineJobForBasemap(parameters);

                // Create the job with the parameters and output location.
                _generateOfflineMapJob = takeMapOfflineTask.GenerateOfflineMap(parameters, packagePath);

                // Handle the progress changed event for the job.
                _generateOfflineMapJob.ProgressChanged += OfflineMapJob_ProgressChanged;

                // Await the job to generate geodatabases, export tile packages, and create the mobile map package.
                GenerateOfflineMapResult results = await _generateOfflineMapJob.GetResultAsync();

                // Check for job failure (writing the output was denied, e.g.).
                if (_generateOfflineMapJob.Status != JobStatus.Succeeded)
                {
                    await Application.Current.MainPage.DisplayAlert("Alert", "Generate offline map package failed.", "OK");
                    BusyIndicator.IsVisible = false;
                }

                // Check for errors with individual layers.
                if (results.LayerErrors.Any())
                {
                    // Build a string to show all layer errors.
                    System.Text.StringBuilder errorBuilder = new System.Text.StringBuilder();
                    foreach (KeyValuePair<Layer, Exception> layerError in results.LayerErrors)
                    {
                        errorBuilder.AppendLine($"{layerError.Key.Id} : {layerError.Value.Message}");
                    }

                    // Show layer errors.
                    string errorText = errorBuilder.ToString();
                    await Application.Current.MainPage.DisplayAlert("Alert", errorText, "OK");
                }

                // Display the offline map.
                MyMapView.Map = results.OfflineMap;

                // Apply the original viewpoint for the offline map.
                MyMapView.SetViewpoint(new Viewpoint(_areaOfInterest));

                // Enable map interaction so the user can explore the offline data.
                MyMapView.InteractionOptions.IsEnabled = true;

                // Hide the "Take map offline" button.
                TakeOfflineArea.IsVisible = false;

                // Show a message that the map is offline.
                MessageArea.IsVisible = true;
            }
            catch (TaskCanceledException)
            {
                // Generate offline map task was canceled.
                await Application.Current.MainPage.DisplayAlert("Alert", "Taking map offline was canceled", "OK");
            }
            catch (Exception ex)
            {
                // Exception while taking the map offline.
                await Application.Current.MainPage.DisplayAlert("Alert", ex.Message, "OK");
            }
            finally
            {
                // Hide the activity indicator when the job is done.
                BusyIndicator.IsVisible = false;
            }
        }

        // Show changes in job progress.
        private void OfflineMapJob_ProgressChanged(object sender, EventArgs e)
        {
            // Get the job.
            GenerateOfflineMapJob job = sender as GenerateOfflineMapJob;

            // Dispatch to the UI thread.
            Device.BeginInvokeOnMainThread(() =>
            {
                // Show the percent complete and update the progress bar.
                Percentage.Text = job.Progress > 0 ? job.Progress.ToString() + " %" : string.Empty;
                ProgressBar.Progress = job.Progress / 100.0;
            });
        }

        private void CancelJobButton_Click(object sender, EventArgs e)
        {
            // The user canceled the job.
            _generateOfflineMapJob.Cancel();
        }

        #endregion Generate offline map

        #region Authentication

        // Constants for OAuth-related values.
        // - The URL of the portal to authenticate with (ArcGIS Online).
        private const string ServerUrl = "https://www.arcgis.com/sharing/rest";

        // - The Client ID for an app registered with the server (the ID below is for a public app created by the ArcGIS Runtime team).
        private const string AppClientId = @"6wMAmbUEX1rvsOb4";

        // - A URL for redirecting after a successful authorization (this must be a URL configured with the app).
        private const string OAuthRedirectUrl = @"forms-samples-app://auth";

        private void SetOAuthInfo()
        {
            // Register the server information with the AuthenticationManager.
            ServerInfo serverInfo = new ServerInfo
            {
                ServerUri = new Uri(ServerUrl),
                TokenAuthenticationType = TokenAuthenticationType.OAuthImplicit,
                OAuthClientInfo = new OAuthClientInfo
                {
                    ClientId = AppClientId,
                    RedirectUri = new Uri(OAuthRedirectUrl)
                }
            };

            // Register this server with AuthenticationManager.
            AuthenticationManager.Current.RegisterServer(serverInfo);

            // Use a function in this class to challenge for credentials.
            AuthenticationManager.Current.ChallengeHandler = new ChallengeHandler(CreateCredentialAsync);

            // Set the OAuthAuthorizeHandler component (this class) for Android or iOS platforms.
#if __ANDROID__ || __IOS__
            AuthenticationManager.Current.OAuthAuthorizeHandler = this;
#endif
        }

        // ChallengeHandler function that will be called whenever access to a secured resource is attempted.
        private async Task<Credential> CreateCredentialAsync(CredentialRequestInfo info)
        {
            Credential credential = null;

            try
            {
                // IOAuthAuthorizeHandler will challenge the user for OAuth credentials.
                credential = await AuthenticationManager.Current.GenerateCredentialAsync(info.ServiceUri);
            }
            catch (TaskCanceledException)
            {
                return credential;
            }
            catch (Exception)
            {
                // Exception will be reported in calling function.
                throw;
            }

            return credential;
        }

        #region IOAuthAuthorizationHandler implementation

        // Use a TaskCompletionSource to track the completion of the authorization.
        private TaskCompletionSource<IDictionary<string, string>> _taskCompletionSource;

        // IOAuthAuthorizeHandler.AuthorizeAsync implementation.
        public Task<IDictionary<string, string>> AuthorizeAsync(Uri serviceUri, Uri authorizeUri, Uri callbackUri)
        {
            // If the TaskCompletionSource is not null, authorization may already be in progress and should be canceled.
            // Try to cancel any existing authentication task.
            _taskCompletionSource?.TrySetCanceled();

            // Create a task completion source.
            _taskCompletionSource = new TaskCompletionSource<IDictionary<string, string>>();
#if __ANDROID__ || __IOS__

#if __ANDROID__
            // Get the current Android Activity.
            Activity activity = (Activity)ArcGISRuntime.Droid.MainActivity.Instance;
#endif
#if __IOS__
            // Get the current iOS ViewController.
            UIViewController viewController = null;
            Device.BeginInvokeOnMainThread(() => { viewController = UIApplication.SharedApplication.KeyWindow.RootViewController; });
#endif
            // Create a new Xamarin.Auth.OAuth2Authenticator using the information passed in.
            OAuth2Authenticator authenticator = new OAuth2Authenticator(
                clientId: AppClientId,
                scope: "",
                authorizeUrl: authorizeUri,
                redirectUrl: callbackUri)
            {
                ShowErrors = false,
                // Allow the user to cancel the OAuth attempt.
                AllowCancel = true
            };

            // Define a handler for the OAuth2Authenticator.Completed event.
            authenticator.Completed += (sender, authArgs) =>
            {
                try
                {
#if __IOS__
                    // Dismiss the OAuth UI when complete.
                    viewController.DismissViewController(true, null);
#endif

                    // Check if the user is authenticated.
                    if (authArgs.IsAuthenticated)
                    {
                        // If authorization was successful, get the user's account.
                        Xamarin.Auth.Account authenticatedAccount = authArgs.Account;

                        // Set the result (Credential) for the TaskCompletionSource.
                        _taskCompletionSource.SetResult(authenticatedAccount.Properties);
                    }
                    else
                    {
                        throw new Exception("Unable to authenticate user.");
                    }
                }
                catch (Exception ex)
                {
                    // If authentication failed, set the exception on the TaskCompletionSource.
                    _taskCompletionSource.TrySetException(ex);

                    // Cancel authentication.
                    authenticator.OnCancelled();
                }
                finally
                {
                    // Dismiss the OAuth login.
#if __ANDROID__
                    activity.FinishActivity(99);
#endif
                }
            };

            // If an error was encountered when authenticating, set the exception on the TaskCompletionSource.
            authenticator.Error += (sndr, errArgs) =>
            {
                // If the user cancels, the Error event is raised but there is no exception ... best to check first.
                if (errArgs.Exception != null)
                {
                    _taskCompletionSource.TrySetException(errArgs.Exception);
                }
                else
                {
                    // Login canceled: dismiss the OAuth login.
                    _taskCompletionSource?.TrySetCanceled();
#if __ANDROID__
                    activity.FinishActivity(99);
#endif
                }

                // Cancel authentication.
                authenticator.OnCancelled();
            };

            // Present the OAuth UI so the user can enter user name and password.
#if __ANDROID__
            Android.Content.Intent intent = authenticator.GetUI(activity);
            activity.StartActivityForResult(intent, 99);
#endif
#if __IOS__
            // Present the OAuth UI (on the app's UI thread) so the user can enter user name and password.
            Device.BeginInvokeOnMainThread(() => { viewController.PresentViewController(authenticator.GetUI(), true, null); });
#endif

#endif // (If Android or iOS)
            // Return completion source task so the caller can await completion.
            return _taskCompletionSource.Task;
        }

        #endregion
    }

    #endregion
}
XAML
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:esriUI="clr-namespace:Esri.ArcGISRuntime.Xamarin.Forms;assembly=Esri.ArcGISRuntime.Xamarin.Forms"
             x:Class="ArcGISRuntimeXamarin.Samples.OfflineBasemapByReference.OfflineBasemapByReference">
    <Grid>
        <esriUI:MapView x:Name="MyMapView" />
        <Frame x:Name="TakeOfflineArea"
               BackgroundColor="White" BorderColor="Black"
               HorizontalOptions="End" VerticalOptions="Start"
               Margin="30" Padding="20" WidthRequest="375">
            <StackLayout HorizontalOptions="Center" VerticalOptions="Center">
                <Button Text="Take map offline"
                        WidthRequest="250"
                        Clicked="TakeMapOfflineButton_Click"
                        IsEnabled="True" />
            </StackLayout>
        </Frame>
        <Frame x:Name="MessageArea"
               IsVisible="False"
               BackgroundColor="White" BorderColor="Black"
               HorizontalOptions="End" VerticalOptions="Start"
               Margin="30" Padding="5" WidthRequest="450">
            <StackLayout>
                <Label HorizontalOptions="Center" VerticalOptions="Center" Margin="10"
                       Text="Map is offline!" />
            </StackLayout>
        </Frame>
        <Grid x:Name="BusyIndicator" BackgroundColor="#807f7f7f" IsVisible="False">
            <Grid HorizontalOptions="Center" VerticalOptions="Center">
                <Grid.RowDefinitions>
                    <RowDefinition Height="auto" />
                    <RowDefinition Height="auto" />
                    <RowDefinition Height="auto" />
                </Grid.RowDefinitions>
                <Label HorizontalOptions="Center" VerticalOptions="Center" Margin="10"
                       TextColor="White" FontSize="18">
                    <Label.FormattedText>
                        <FormattedString>
                            <Span Text="Generating offline map... " />
                            <Span x:Name="Percentage" Text="" />
                        </FormattedString>
                    </Label.FormattedText>
                </Label>
                <ProgressBar x:Name="ProgressBar"
                             Grid.Row="1"
                             IsEnabled="True"
                             HorizontalOptions="Center" VerticalOptions="Center"
                             WidthRequest="100" HeightRequest="10" Margin="0,0,0,10" />
                <Button Text="Cancel"
                        Grid.Row="2"
                        Clicked="CancelJobButton_Click"
                        HorizontalOptions="Center"
                        WidthRequest="100" />
            </Grid>
        </Grid>
        <Grid x:Name="LoadingIndicator"
              BackgroundColor="#807f7f7f"
              IsVisible="True">
            <Grid HorizontalOptions="Center" VerticalOptions="Center">
                <Grid.RowDefinitions>
                    <RowDefinition Height="auto" />
                    <RowDefinition Height="auto" />
                </Grid.RowDefinitions>
                <Label Text="Loading online map..."
                       TextColor="White" FontSize="18"
                       Margin="10" />
                <ProgressBar Grid.Row="1"
                             IsEnabled="True"
                             WidthRequest="100" HeightRequest="10"
                             HorizontalOptions="Center" VerticalOptions="Center" />
            </Grid>
        </Grid>
    </Grid>
</ContentPage>
See Also
Additional Examples
Hyperlink to ExampleDescription
GenerateOfflineMapTake a web map offline.
GenerateOfflineMapWithOverridesTake a web map offline with additional options for each layer.
OfflineBasemapByReferenceUse the `OfflineMapTask` to take a web map offline, but instead of downloading an online basemap, use one which is already on the device.