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
}
}
}