Determine whether a layer is currently visible.
Use case
The view status includes information on the loading state of layers and whether layers are visible at a given scale. You might change how a layer is displayed in a layer list to communicate whether it is being viewed in the map. For example, you could show a loading spinner next to its name when the view status is loading
, gray out the name when notVisible
or outOfScale
, show the name normally when active
, or with an error icon when the state is warning
or error
.
How to use the sample
When the feature layer is loaded, pan and zoom around the map. Note how the AGSLayerViewState
flags change; for example, outOfScale
becomes true when the map is scaled outside of the layer's min and max scale range. Tap the toggle to hide the layer and observe the view state change to notVisible
.
Disconnect from the network and pan around the map to see the warning
status of the different layers when they cannot fetch online data. Reconnect to the network to see the warning disappear.
How it works
- Create an
AGSMap
with some operational layers. - Set the map on an
AGSMapView
. - Assign a closure to
layerViewStateChangedHandler
of the map view, which get executed every time a layer's view status changes. - Get the
AGSLayer
and the current viewstatus
of typeAGSLayerViewState
defining the new state.
Relevant API
- AGSLayer
- AGSLayerViewState
- AGSMap
- AGSMapView
About the data
The Satellite (MODIS) Thermal Hotspots and Fire Activity layer presents detectable thermal activity from MODIS satellites for the last 48 hours. MODIS Global Fires is a product of NASA’s Earth Observing System Data and Information System (EOSDIS), part of NASA's Earth Science Data. EOSDIS integrates remote sensing and GIS technologies to deliver global MODIS hotspot/fire locations to natural resource managers and other stakeholders around the World.
Additional information
The following are members of the AGSLayerViewState
enum:
active
: The layer in the view is active.notVisible
: The layer in the view is not visible.outOfScale
: The layer in the view is out of scale. A status ofoutOfScale
indicates that the view is zoomed outside of the scale range of the layer. If the view is zoomed too far in (e.g. to a street level), it is beyond the max scale defined for the layer. If the view has zoomed too far out (e.g. to global scale), it is beyond the min scale defined for the layer.loading
: The layer in the view is loading. Once loading has completed, the layer will be available for display in the view. If there was a problem loading the layer, the status will be set to error.error
: The layer in the view has an unrecoverable error. When the status iserror
, the layer cannot be rendered in the view. For example, it may have failed to load, be an unsupported layer type, or contain invalid data.warning
: The layer in the view has a non-breaking problem with its display, such as incomplete information (e.g. by requesting more features than the max feature count of a service) or a network request failure.
Tags
layer, load, map, status, view, visibility
Sample Code
// Copyright 2015 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.
import UIKit
import ArcGIS
class LayerStatusViewController: UIViewController {
// MARK: Instance properties and methods
/// The map view managed by the view controller.
@IBOutlet weak var mapView: AGSMapView! {
didSet {
mapView.map = makeMap(featureLayer: featureLayer)
mapView.setViewpoint(AGSViewpoint(center: AGSPoint(x: -11e6, y: 45e5, spatialReference: .webMercator()), scale: 2e7))
mapView.layerViewStateChangedHandler = { [weak self] layer, state in
guard let self = self else { return }
// Only check the view state of the feature layer.
guard layer == self.featureLayer else { return }
DispatchQueue.main.async {
if let error = state.error {
self.presentAlert(error: error)
}
self.setStatus(message: self.viewStatusString(state.status))
}
}
}
}
/// The label to display layer view status.
@IBOutlet weak var statusLabel: UILabel!
/// The feature layer loaded from a portal item.
let featureLayer: AGSFeatureLayer = {
let portalItem = AGSPortalItem(url: URL(string: "https://runtime.maps.arcgis.com/home/item.html?id=b8f4033069f141729ffb298b7418b653")!)!
let featureLayer = AGSFeatureLayer(item: portalItem, layerID: 0)
featureLayer.minScale = 1e8
featureLayer.maxScale = 6e6
return featureLayer
}()
/// Create a map with an `AGSFeatureLayer` added to its operational layers.
///
/// - Parameter featureLayer: An `AGSFeatureLayer` object.
/// - Returns: An `AGSMap` object.
func makeMap(featureLayer: AGSFeatureLayer) -> AGSMap {
let map = AGSMap(basemapStyle: .arcGISTopographic)
map.operationalLayers.add(featureLayer)
return map
}
// MARK: UI
func setStatus(message: String) {
statusLabel.text = message
}
/// Get a string for current statuses.
///
/// - Parameter status: An `AGSLayerViewStatus` OptionSet that indicates the layer's statuses.
/// - Returns: A comma separated string to represent current statuses.
func viewStatusString(_ status: AGSLayerViewStatus) -> String {
var statuses = [String]()
if status.contains(.active) {
statuses.append("Active")
}
if status.contains(.notVisible) {
statuses.append("Not Visible")
}
if status.contains(.outOfScale) {
statuses.append("Out of Scale")
}
if status.contains(.loading) {
statuses.append("Loading")
}
if status.contains(.error) {
statuses.append("Error")
}
if status.contains(.warning) {
statuses.append("Warning")
}
if !statuses.isEmpty {
return statuses.joined(separator: ", ")
} else {
return "Unknown"
}
}
// MARK: Actions
@IBAction func layerVisibilitySwitchValueChanged(_ sender: UISwitch) {
featureLayer.isVisible = sender.isOn
}
// MARK: UIViewController
override func viewDidLoad() {
super.viewDidLoad()
// Add the source code button item to the right of navigation bar.
(self.navigationItem.rightBarButtonItem as? SourceCodeBarButtonItem)?.filenames = ["LayerStatusViewController"]
// Avoid the overlap between the status label and the map content.
mapView.contentInset.top = 2 * statusLabel.font.lineHeight
}
}