Identify graphics

This sample demonstrates how to identify graphics in a graphics overlay. When you tap on a graphic on the map, you will see an alert message displayed.

Identify graphics

Code

// Copyright 2016 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.

using Esri.ArcGISRuntime.Data;
using Esri.ArcGISRuntime.Geometry;
using Esri.ArcGISRuntime.Mapping;
using Esri.ArcGISRuntime.Symbology;
using Esri.ArcGISRuntime.UI;
using Esri.ArcGISRuntime.UI.Controls;
using Foundation;
using System.Collections.Generic;
using UIKit;

namespace ArcGISRuntimeXamarin.Samples.IdentifyGraphics
{
    [Register("IdentifyGraphics")]
    public class IdentifyGraphics : UIViewController
    {
        // Constant holding offset where the MapView control should start
        private const int yPageOffset = 60;

        // Create and hold reference to the used MapView
        private MapView _myMapView = new MapView();

        // Graphics overlay to host graphics
        private GraphicsOverlay _polygonOverlay;

        public IdentifyGraphics()
        { 
            Title = "Identify graphics";
        }

        public override void ViewDidLoad()
        {
            base.ViewDidLoad();

            // Create the UI, setup the control references and execute initialization 
            CreateLayout();
            Initialize();
        }

        public override void ViewDidLayoutSubviews()
        {
            // Setup the visual frame for the MapView
            _myMapView.Frame = new CoreGraphics.CGRect(0, 0, View.Bounds.Width, View.Bounds.Height);
        }

        private void Initialize()
        {
            // Create a map with 'Imagery with Labels' basemap and an initial location
            Map myMap = new Map(Basemap.CreateTopographic());

            // Create graphics overlay with graphics
            CreateOverlay();

            // Hook into tapped event
            _myMapView.GeoViewTapped += OnMapViewTapped;

            // Assign the map to the MapView
            _myMapView.Map = myMap;
        }

        private void CreateOverlay()
        {
            // Create polygon builder and add polygon corners into it
            PolygonBuilder builder = new PolygonBuilder(SpatialReferences.WebMercator);
            builder.AddPoint(new MapPoint(-20e5, 20e5));
            builder.AddPoint(new MapPoint(20e5, 20e5));
            builder.AddPoint(new MapPoint(20e5, -20e5));
            builder.AddPoint(new MapPoint(-20e5, -20e5));

            // Get geometry from the builder
            Polygon polygonGeometry = builder.ToGeometry();

            // Create symbol for the polygon
            SimpleFillSymbol polygonSymbol = new SimpleFillSymbol(
                SimpleFillSymbolStyle.Solid,
                System.Drawing.Color.Yellow,
                null);

            // Create new graphic
            Graphic polygonGraphic = new Graphic(polygonGeometry, polygonSymbol);

            // Create overlay to where graphics are shown
            _polygonOverlay = new GraphicsOverlay();
            _polygonOverlay.Graphics.Add(polygonGraphic);

            // Add created overlay to the MapView
            _myMapView.GraphicsOverlays.Add(_polygonOverlay);
        }

        private async void OnMapViewTapped(object sender, GeoViewInputEventArgs e)
        {
            var tolerance = 10d; // Use larger tolerance for touch
            var maximumResults = 1; // Only return one graphic  
            var onlyReturnPopups = false; // Don't only return popups

            // Use the following method to identify graphics in a specific graphics overlay
            IdentifyGraphicsOverlayResult identifyResults = await _myMapView.IdentifyGraphicsOverlayAsync(
                 _polygonOverlay,
                 e.Position,
                 tolerance, 
                 onlyReturnPopups, 
                 maximumResults);

            // Check if we got results
            if (identifyResults.Graphics.Count > 0)
            {
                // Make sure that the UI changes are done in the UI thread
                InvokeOnMainThread(() =>
                {
                    var alert = new UIAlertView("", "Tapped on graphic", null, "OK", null);
                    alert.Show();
                });
            }
        }

        private void CreateLayout()
        {
            // Add MapView to the page
            View.AddSubviews(_myMapView);
        }
    }
}


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