Identify graphics

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# 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.

<img src="IdentifyGraphics.jpg" width="350"/>

Code

XAML

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"             
             xmlns:esriUI="clr-namespace:Esri.ArcGISRuntime.Xamarin.Forms;assembly=Esri.ArcGISRuntime.Xamarin.Forms"
             xmlns:mapping="clr-namespace:Esri.ArcGISRuntime.Mapping;assembly=Esri.ArcGISRuntime" 
             x:Class="ArcGISRuntime.Samples.IdentifyGraphics.IdentifyGraphics">
  <Grid>
    <esriUI:MapView x:Name="MyMapView"/>
  </Grid>
</ContentPage>

C#

// 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.Mapping;
using Esri.ArcGISRuntime.Symbology;
using Esri.ArcGISRuntime.Geometry;
using Esri.ArcGISRuntime.UI;
using Xamarin.Forms;
using Esri.ArcGISRuntime.Data;
using Colors = System.Drawing.Color;

namespace ArcGISRuntime.Samples.IdentifyGraphics
{
    [ArcGISRuntime.Samples.Shared.Attributes.Sample(
        "Identify graphics",
        "GraphicsOverlay",
        "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.",
        "")]
    public partial class IdentifyGraphics : ContentPage
    {
        // Graphics overlay to host graphics
        private GraphicsOverlay _polygonOverlay;

        public IdentifyGraphics()
        {
            InitializeComponent();

            Title = "Identify graphics";

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

        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,
               Colors.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, Esri.ArcGISRuntime.Xamarin.Forms.GeoViewInputEventArgs e)
        {
            var tolerance = 10d; // Use larger tolerance for touch
            var maximumResults = 1; // Only return one graphic  
            var onlyReturnPopups = false; // Don't return only 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
                Device.BeginInvokeOnMainThread(async () => {
                    await DisplayAlert("", "Tapped on graphic", "OK");
                });
            }
        }
    }
}