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WFS layer with features for the current extent

WFS layer


// 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:
// 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 Esri.ArcGISRuntime.Data;
using Esri.ArcGISRuntime.Geometry;
using Esri.ArcGISRuntime.Mapping;
using Esri.ArcGISRuntime.Symbology;
using Esri.ArcGISRuntime.UI.Controls;
using Foundation;
using System;
using System.Diagnostics;
using System.Drawing;
using UIKit;

namespace ArcGISRuntimeXamarin.Samples.DisplayWfs
        "Display a WFS layer",
        "Display a layer from a WFS service, requesting only features for the current extent.",
    public class DisplayWfs : UIViewController
        // Hold references to UI controls.
        private MapView _myMapView;
        private UIActivityIndicatorView _loadingProgressBar;

        // Hold a reference to the WFS feature table.
        private WfsFeatureTable _featureTable;

        // Constants for the service URL and layer name.
        private const string ServiceUrl = "";
        // Note that the layer name is defined by the service. The layer name can be accessed via WfsLayerInfo.Name. 
        private const string LayerName = "Seattle_Downtown_Features:Buildings";

        public DisplayWfs()
            Title = "Display a WFS layer";

        private async void Initialize()
            // Create the map with topographic basemap.
            _myMapView.Map = new Map(Basemap.CreateTopographic());

                // Create the feature table from URI and layer name.
                _featureTable = new WfsFeatureTable(new Uri(ServiceUrl), LayerName);

                // Set the 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.
                _featureTable.FeatureRequestMode = FeatureRequestMode.ManualCache;

                // Load the table.
                await _featureTable.LoadAsync();

                // Create a feature layer to visualize the WFS features.
                FeatureLayer wfsFeatureLayer = new FeatureLayer(_featureTable);

                // Apply a renderer.
                wfsFeatureLayer.Renderer = new SimpleRenderer(new SimpleLineSymbol(SimpleLineSymbolStyle.Solid, Color.Red, 3));

                // Add the layer to the map.

                // Use the navigation completed event to populate the table with the features needed for the current extent.
                _myMapView.NavigationCompleted += MapView_NavigationCompleted;

                // Zoom to a small area within the dataset by default.
                MapPoint topLeft = new MapPoint(-122.341581, 47.617207, SpatialReferences.Wgs84);
                MapPoint bottomRight = new MapPoint(-122.332662, 47.613758, SpatialReferences.Wgs84);
                await _myMapView.SetViewpointGeometryAsync(new Envelope(topLeft, bottomRight));
            catch (Exception e)
                new UIAlertView("Couldn't load sample.", e.ToString(), (IUIAlertViewDelegate) null, "OK", null).Show();

        private async void MapView_NavigationCompleted(object sender, EventArgs e)
            // Show the loading bar.

            // Get the current extent.
            Envelope currentExtent = _myMapView.VisibleArea.Extent;

            // Create a query based on the current visible extent.
            QueryParameters visibleExtentQuery = new QueryParameters();
            visibleExtentQuery.Geometry = currentExtent;
            visibleExtentQuery.SpatialRelationship = SpatialRelationship.Intersects;

                // Populate the table with the query, leaving existing table entries intact.
                // Setting outFields to null requests all features.
                await _featureTable.PopulateFromServiceAsync(visibleExtentQuery, false, null);
            catch (Exception exception)
                new UIAlertView("Couldn't populate table", exception.ToString(), (IUIAlertViewDelegate) null, "OK", null).Show();
                // Hide the loading bar.

        public override void LoadView()
            // Create the views.
            View = new UIView();

            _myMapView = new MapView();
            _myMapView.TranslatesAutoresizingMaskIntoConstraints = false;

            _loadingProgressBar = new UIActivityIndicatorView(UIActivityIndicatorViewStyle.WhiteLarge)
                HidesWhenStopped = true, 
                BackgroundColor = UIColor.FromWhiteAlpha(0, .6f),
                TranslatesAutoresizingMaskIntoConstraints = false

            UILabel helpLabel = new UILabel
                Text = "Pan and zoom to see features.",
                AdjustsFontSizeToFitWidth = true,
                TextAlignment = UITextAlignment.Center,
                BackgroundColor = UIColor.FromWhiteAlpha(0, .6f),
                TextColor = UIColor.White,
                Lines = 1,
                TranslatesAutoresizingMaskIntoConstraints = false

            // Add the views.
            View.AddSubviews(_myMapView, helpLabel, _loadingProgressBar);

            // Lay out the views.
            NSLayoutConstraint.ActivateConstraints(new []

        public override void ViewDidLoad()

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