Take a web map offline.
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
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.
How it works
- Create an
ArcGISMapwith aPortalItempointing to the web map. - Create
GenerateOfflineMapParametersspecifying the download area geometry, minimum scale, and maximum scale. - Create an
OfflineMapTaskwith the map. - Create the
OfflineMapJobwithOfflineMapTask.generateOfflineMap(params, downloadDirectoryPath)and start it withOfflineMapJob.start(). - When the job is done, get the offline map with
OfflineMapJob.result.offlineMap.
Relevant API
- GenerateOfflineMapJob
- GenerateOfflineMapParameters
- GenerateOfflineMapResult
- OfflineMapTask
- Portal
About the data
The map used in this sample shows the stormwater 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 parameter overrides for feature layers, or by using local basemaps to achieve more customised results. Also, this sample uses the GeoView-Compose Toolkit module to be able to implement a composable MapView.
Tags
download, geoview-compose, offline, save, web map
Sample Code
/* Copyright 2024 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. * */ package com.esri.arcgismaps.sample.generateofflinemap.components import android.app.Application import androidx.compose.material3.SnackbarHostState import androidx.compose.runtime.getValue import androidx.compose.runtime.mutableIntStateOf import androidx.compose.runtime.mutableStateOf import androidx.compose.runtime.setValue import androidx.compose.ui.unit.IntSize import androidx.lifecycle.AndroidViewModel import androidx.lifecycle.viewModelScope import com.arcgismaps.geometry.Envelope import com.arcgismaps.mapping.ArcGISMap import com.arcgismaps.mapping.PortalItem import com.arcgismaps.mapping.symbology.SimpleLineSymbol import com.arcgismaps.mapping.symbology.SimpleLineSymbolStyle import com.arcgismaps.mapping.view.Graphic import com.arcgismaps.mapping.view.GraphicsOverlay import com.arcgismaps.mapping.view.ScreenCoordinate import com.arcgismaps.portal.Portal import com.arcgismaps.tasks.offlinemaptask.GenerateOfflineMapJob import com.arcgismaps.tasks.offlinemaptask.GenerateOfflineMapParameters import com.arcgismaps.tasks.offlinemaptask.OfflineMapTask import com.arcgismaps.toolkit.geoviewcompose.MapViewProxy import com.esri.arcgismaps.sample.generateofflinemap.R import com.esri.arcgismaps.sample.sampleslib.components.MessageDialogViewModel import kotlinx.coroutines.Dispatchers import kotlinx.coroutines.launch import java.io.File class MapViewModel(private val application: Application) : AndroidViewModel(application) { // Create a symbol to show a box around the extent we want to download private val downloadArea: Graphic = Graphic( symbol = SimpleLineSymbol( style = SimpleLineSymbolStyle.Solid, color = com.arcgismaps.Color.red, width = 2F ) ) // Create graphic overlay to add graphics val graphicsOverlay = GraphicsOverlay() // Create a ViewModel to handle dialog interactions. val messageDialogVM: MessageDialogViewModel = MessageDialogViewModel() // Define button to take a map offline var takeMapOfflineButtonText by mutableStateOf(application.getString(R.string.take_map_offline)) private set // Defined to send messages related to offlineMapJob val snackbarHostState = SnackbarHostState() // Define map that returns an ArcGISMap var map by mutableStateOf(ArcGISMap()) private set // Determinate job progress loading dialog visibility state var showJobProgressDialog by mutableStateOf(false) private set // Determinate job progress percentage var offlineMapJobProgress by mutableIntStateOf(0) private set // Job used to run the offlineMap task on a service private var offlineMapJob: GenerateOfflineMapJob? = null // Create a MapViewProxy to handle MapView operations val mapViewProxy = MapViewProxy() // Create an IntSize to retrieve dimensions of the map private var mapViewSize by mutableStateOf(IntSize(0, 0)) init { // Set up the portal item to take offline setUpMap() } /** * Sets up a portal item and displays map area to take offline */ private fun setUpMap() { // Create a portal item with the itemId of the web map val portal = Portal(application.getString(R.string.portal_url)) val portalItem = PortalItem(portal, application.getString(R.string.item_id)) // Clear, then add the download graphic to the graphics overlay graphicsOverlay.graphics.clear() graphicsOverlay.graphics.add(downloadArea) map = ArcGISMap(portalItem) viewModelScope.launch(Dispatchers.Main) { map.load() .onFailure { messageDialogVM.showMessageDialog( title = it.message.toString() ) } .onSuccess { // Limit the map scale to the largest layer scale map.maxScale = map.operationalLayers[6].maxScale ?: 0.0 map.minScale = map.operationalLayers[6].minScale ?: 0.0 } } } /** * Generate an offline map job with the default [GenerateOfflineMapParameters] * */ fun createOfflineMapJob() { // Offline map path val offlineMapPath = application.getExternalFilesDir(null)?.path + File.separator + "offlineMap" // Delete any offline map already in the cache File(offlineMapPath).deleteRecursively() // Specify the extent, min scale, and max scale as parameters var minScale: Double = map.minScale ?: 0.0 val maxScale: Double = map.maxScale ?: 0.0 // Variable minScale must always be larger than maxScale if (minScale <= maxScale) { minScale = maxScale + 1 } // Get the geometry of the download area val geometry = downloadArea.geometry ?: return messageDialogVM.showMessageDialog( title = "Could not get geometry of the downloadArea" ) // Set the offline map parameters val generateOfflineMapParameters = GenerateOfflineMapParameters( areaOfInterest = geometry, minScale = minScale, maxScale = maxScale ).apply { // Set job to cancel on any errors continueOnErrors = false } // Create an offline map task with the map val offlineMapTask = OfflineMapTask(onlineMap = map) viewModelScope.launch(Dispatchers.Main) { offlineMapTask.load().getOrElse { messageDialogVM.showMessageDialog( title = it.message.toString(), description = it.cause.toString() ) } } // Create an offline map job with the download directory path and parameters and start the job offlineMapJob = offlineMapTask.createGenerateOfflineMapJob( parameters = generateOfflineMapParameters, downloadDirectoryPath = offlineMapPath ) runOfflineMapJob() } /** * Starts the [GenerateOfflineMapJob], shows the progress dialog and * displays the result offline map to the MapView */ private fun runOfflineMapJob() { offlineMapJob?.let { offlineMapJob -> // Show the Job Progress Dialog showJobProgressDialog = true with(viewModelScope) { // Create a flow-collection for the job's progress launch(Dispatchers.Main) { offlineMapJob.progress.collect { progress -> // Display the current job's progress value offlineMapJobProgress = progress } } launch(Dispatchers.IO) { // Start the job and wait for Job result offlineMapJob.start() offlineMapJob.result().onSuccess { // Set the offline map result as the displayed map and clear the red bounding box graphic map = it.offlineMap graphicsOverlay.graphics.clear() // Change the button text to Reset Map once job is done successfully takeMapOfflineButtonText = application.getString(R.string.reset_map) // Dismiss the progress dialog showJobProgressDialog = false // Show user where map was locally saved snackbarHostState.showSnackbar(message = "Map saved at: " + offlineMapJob.downloadDirectoryPath) }.onFailure { throwable -> messageDialogVM.showMessageDialog( title = throwable.message.toString(), description = throwable.cause.toString() ) showJobProgressDialog = false } } } } } fun cancelOfflineMapJob() { with(viewModelScope) { launch(Dispatchers.IO) { offlineMapJob?.cancel() } launch(Dispatchers.Main) { snackbarHostState.showSnackbar(message = "User canceled.") } } } fun updateMapViewSize(size: IntSize) { mapViewSize = size } /** * Clear the preview map and set up mapView again */ fun resetButtonClick() { // Add the download graphic to the graphics overlay graphicsOverlay.graphics.clear() // Change button text to Take Map Offline on reset takeMapOfflineButtonText = application.getString(R.string.take_map_offline) // Set up the portal item to take offline setUpMap() } /** * Use map view's size to determine dimensions of the map to get the download offline area * and use [MapViewProxy] to assist in converting screen points to map points */ fun calculateDownloadOfflineArea() { // Upper left corner of the area to take offline val minScreenPoint = ScreenCoordinate(200.0, 200.0) // Lower right corner of the downloaded area val maxScreenPoint = ScreenCoordinate( x = mapViewSize.width - 200.0, y = mapViewSize.height - 200.0 ) // Convert screen points to map points val minPoint = mapViewProxy.screenToLocationOrNull(minScreenPoint) val maxPoint = mapViewProxy.screenToLocationOrNull(maxScreenPoint) // Create an envelope to set the download area's geometry using the defined bounds if (minPoint != null && maxPoint != null) { val envelope = Envelope(minPoint, maxPoint) downloadArea.geometry = envelope } } }