Identify graphics

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage x:Class="ArcGIS.Samples.IdentifyGraphics.IdentifyGraphics"
             xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:esriUI="clr-namespace:Esri.ArcGISRuntime.Maui;assembly=Esri.ArcGISRuntime.Maui">
    <Grid>
        <esriUI:MapView x:Name="MyMapView" />
    </Grid>
</ContentPage>

// Copyright 2022 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 Colors = System.Drawing.Color;

namespace ArcGIS.Samples.IdentifyGraphics
{
    [ArcGIS.Samples.Shared.Attributes.Sample(
        name: "Identify graphics",
        category: "GraphicsOverlay",
        description: "Display an alert message when a graphic is clicked.",
        instructions: "Select a graphic to identify it. You will see an alert message displayed.",
        tags: new[] { "graphics", "identify" })]
    public partial class IdentifyGraphics : ContentPage
    {
        // Graphics overlay to host graphics
        private GraphicsOverlay _polygonOverlay;

        public IdentifyGraphics()
        {
            InitializeComponent();

            // 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(BasemapStyle.ArcGISTopographic);

            // 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.Maui.GeoViewInputEventArgs e)
        {
            double tolerance = 10d; // Use larger tolerance for touch
            int maximumResults = 1; // Only return one graphic
            bool onlyReturnPopups = false; // Don't return only popups

            try
            {
                // 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
                    Microsoft.Maui.ApplicationModel.MainThread.BeginInvokeOnMainThread(async () =>
                    {
                        await Application.Current.Windows[0].Page.DisplayAlert("", "Tapped on graphic", "OK");
                    });
                }
            }
            catch (Exception ex)
            {
                await Application.Current.Windows[0].Page.DisplayAlert("Error", ex.ToString(), "OK");
            }
        }
    }
}