Display a WFS layer

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Sample viewer app

Display a layer from a WFS service, requesting only features for the current extent.

Display a WFS layer sample

Use case

WFS is an open standard with functionality similar to ArcGIS feature services. Runtime support for WFS allows you to interoperate with open systems, which are often used in inter-agency efforts, like those for disaster relief.

How to use the sample

Pan and zoom to see features within the current map extent.

How it works

  1. Create an AGSWFSFeatureTable with a URL.
  2. Set the feature request mode to manualCache.
  3. Create an AGSFeatureLayer from the feature table and add it to the map.
  4. Whenever map's view point is changed, use AGSWFSFeatureTable.populateFromService(with:clearCache:outFields:completion:) to load the table with data for the current visible extent.

Relevant API

  • AGSFeatureLayer
  • AGSGeoView.viewpointChangeHandler
  • AGSWFSFeatureTable
  • AGSWFSFeatureTable.populateFromService

About the data

This service shows building footprints for downtown Seattle. For additional information, see the underlying service on ArcGIS Online.

Tags

browse, catalog, feature, interaction cache, layers, OGC, service, web, WFS

Sample Code

DisplayWFSViewController.swift
                                                                                                        
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// 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.

import UIKit
import ArcGIS

class DisplayWFSViewController: UIViewController {
    @IBOutlet private weak var mapView: AGSMapView!
    private var wfsFeatureTable: AGSWFSFeatureTable!
    private var lastQuery: AGSCancelable?

    override func viewDidLoad() {
        super.viewDidLoad()

        // Initialize a map with topographic basemap
        let map = AGSMap(basemapStyle: .arcGISTopographic)

        // A URL to the GetCapabilities endpoint of a WFS service
        let wfsServiceURL = URL(string: "https://dservices2.arcgis.com/ZQgQTuoyBrtmoGdP/arcgis/services/Seattle_Downtown_Features/WFSServer?service=wfs&request=getcapabilities")!

        // Name of the table to load
        let wfsTableName = "Seattle_Downtown_Features:Buildings"

        // Initialize a WFS feature table with service URL and uniquely identifying table name
        wfsFeatureTable = AGSWFSFeatureTable(url: wfsServiceURL, tableName: wfsTableName)

        // Set feature request mode to manual - only manual is supported at v100.5.
        // In this mode, you must manually populate the table - panning and zooming won't request features automatically.
        wfsFeatureTable.featureRequestMode = .manualCache

        // Initialize a feature layer from WFS feature table
        let wfsFeatureLayer = AGSFeatureLayer(featureTable: self.wfsFeatureTable)

        // Create a simple renderer
        let simpleLineSymbol = AGSSimpleLineSymbol(style: .solid, color: .red, width: 3.0)
        let renderer = AGSSimpleRenderer(symbol: simpleLineSymbol)

        // Apply renderer to feature layer
        wfsFeatureLayer.renderer = renderer

        // Add feature layer to the map
        map.operationalLayers.add(wfsFeatureLayer)

        // Query for features whenever map's viewpoint changes
        self.mapView.viewpointChangedHandler = { [weak self] in
            DispatchQueue.main.async {
                self?.populateFeaturesFromQuery()
            }
        }

        // Assign the map to the map view
        mapView.map = map
        mapView.setViewpoint(AGSViewpoint(targetExtent: AGSEnvelope(xMin: -122.341581, yMin: 47.613758, xMax: -122.332662, yMax: 47.617207, spatialReference: .wgs84())))

        // Add the source code button item to the right of navigation bar
        (navigationItem.rightBarButtonItem as! SourceCodeBarButtonItem).filenames = ["DisplayWFSViewController"]
    }

    private func populateFeaturesFromQuery() {
        // If there is an existing query request, cancel it
        if let lastQuery = self.lastQuery {
            lastQuery.cancel()
        }
        // Create query parameters
        let params = AGSQueryParameters()
        params.geometry = self.mapView.visibleArea?.extent
        params.spatialRelationship = .intersects

        // Show progress
        UIApplication.shared.showProgressHUD(message: "Querying")

        // Populate features based on query
        self.lastQuery = self.wfsFeatureTable.populateFromService(with: params, clearCache: true, outFields: ["*"]) { [weak self] (result: AGSFeatureQueryResult?, error: Error?) in
            // Check and get results
            if let result = result {
                // The resulting features should be displayed on the map
                // Print the count of features
                print("Populated \(result.featureEnumerator().allObjects.count) features.")
            }
            // Check for error. If it's a user canceled error, do nothing.
            // Otherwise, display an alert.
            else if let error = error {
                if (error as NSError).code != NSUserCancelledError {
                    self?.presentAlert(error: error)
                } else {
                    return
                }
            }
            // Hide Progress
            UIApplication.shared.hideProgressHUD()
        }
    }
}

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