Query map image sublayer

<UserControl x:Class="ArcGIS.WinUI.Samples.MapImageSublayerQuery.MapImageSublayerQuery"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:esriUI="using:Esri.ArcGISRuntime.UI.Controls">
    <Grid>
        <esriUI:MapView x:Name="MyMapView" />
        <Border Style="{StaticResource BorderStyle}">
            <Grid>
                <Grid.RowDefinitions>
                    <RowDefinition />
                    <RowDefinition />
                    <RowDefinition />
                </Grid.RowDefinitions>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition />
                    <ColumnDefinition />
                </Grid.ColumnDefinitions>
                <TextBlock Grid.Row="0"
                           Grid.Column="0"
                           Margin="0,0,0,5"
                           HorizontalAlignment="Right"
                           VerticalAlignment="Center"
                           FontWeight="SemiBold"
                           Text="[POP2000] &gt; " />
                <TextBox x:Name="PopulationTextBox"
                         Grid.Row="0"
                         Grid.Column="1"
                         Margin="5,0,0,5"
                         HorizontalAlignment="Stretch"
                         VerticalAlignment="Center"
                         HorizontalContentAlignment="Right"
                         Text="1810000" />
                <Button x:Name="QuerySublayers"
                        Grid.Row="2"
                        Grid.Column="0"
                        Grid.ColumnSpan="2"
                        HorizontalAlignment="Stretch"
                        Click="QuerySublayers_Click"
                        Content="Query in extent" />
            </Grid>
        </Border>
    </Grid>
</UserControl>

// Copyright 2018 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 Microsoft.UI.Xaml;
using System;
using System.Drawing;

namespace ArcGIS.WinUI.Samples.MapImageSublayerQuery
{
    [ArcGIS.Samples.Shared.Attributes.Sample(
        name: "Query map image sublayer",
        category: "Layers",
        description: "Find features in a sublayer based on attributes and location.",
        instructions: "Specify a minimum population in the input field (values under 1810000 will produce a selection in all layers) and click the query button to query the sublayers in the current view extent. After a short time, the results for each sublayer will appear as graphics.",
        tags: new[] { "search and query" })]
    public partial class MapImageSublayerQuery
    {
        // Use a private variable to reference the graphics overlay for showing selected features.
        private GraphicsOverlay _selectedFeaturesOverlay;

        public MapImageSublayerQuery()
        {
            InitializeComponent();

            // Initialize the map to show the USA map image layer.
            Initialize();
        }

        private void Initialize()
        {
            // Create a new Map with a vector streets basemap.
            Map myMap = new Map(BasemapStyle.ArcGISStreets);

            // Create and set the map's initial view point.
            MapPoint initialLocation = new MapPoint(-12716000.00, 4170400.00, SpatialReferences.WebMercator);
            myMap.InitialViewpoint = new Viewpoint(initialLocation, 6000000);

            // Create the URI to the USA map service.
            Uri usaServiceUri = new Uri("https://sampleserver6.arcgisonline.com/arcgis/rest/services/USA/MapServer");

            // Create a new ArcGISMapImageLayer that uses the service URI.
            ArcGISMapImageLayer usaMapImageLayer = new ArcGISMapImageLayer(usaServiceUri);

            // Add the layer to the map.
            myMap.OperationalLayers.Add(usaMapImageLayer);

            // Assign the map to the MapView.
            MyMapView.Map = myMap;

            // Add a graphics overlay to show selected features.
            _selectedFeaturesOverlay = new GraphicsOverlay();
            MyMapView.GraphicsOverlays.Add(_selectedFeaturesOverlay);
        }

        private async void QuerySublayers_Click(object sender, RoutedEventArgs e)
        {
            // Clear selected features from the graphics overlay.
            _selectedFeaturesOverlay.Graphics.Clear();

            // If the population value entered is not numeric, warn the user and exit.
            double populationNumber = 0.0;
            if (!double.TryParse(PopulationTextBox.Text.Trim(), out populationNumber))
            {
                var dialog = new MessageDialog2("The population value must be numeric.", "Query error");
                _ = dialog.ShowAsync();
                return;
            }

            // Get the USA map image layer (the first and only operational layer in the map).
            ArcGISMapImageLayer usaMapImageLayer = (ArcGISMapImageLayer)MyMapView.Map.OperationalLayers[0];

            try
            {
                // Use a utility method on the map image layer to load all the sublayers and tables.
                await usaMapImageLayer.LoadTablesAndLayersAsync();

                // Get the sublayers of interest (skip 'Highways' since it doesn't have the POP2000 field).
                ArcGISMapImageSublayer citiesSublayer = (ArcGISMapImageSublayer)usaMapImageLayer.Sublayers[0];
                ArcGISMapImageSublayer statesSublayer = (ArcGISMapImageSublayer)usaMapImageLayer.Sublayers[2];
                ArcGISMapImageSublayer countiesSublayer = (ArcGISMapImageSublayer)usaMapImageLayer.Sublayers[3];

                // Get the service feature table for each of the sublayers.
                ServiceFeatureTable citiesTable = citiesSublayer.Table;
                ServiceFeatureTable statesTable = statesSublayer.Table;
                ServiceFeatureTable countiesTable = countiesSublayer.Table;

                // Create the query parameters that will find features in the current extent with a population greater than the value entered.
                QueryParameters populationQuery = new QueryParameters
                {
                    WhereClause = "POP2000 > " + PopulationTextBox.Text,
                    Geometry = MyMapView.GetCurrentViewpoint(ViewpointType.BoundingGeometry).TargetGeometry
                };

                // Query each of the sublayers with the query parameters.
                FeatureQueryResult citiesQueryResult = await citiesTable.QueryFeaturesAsync(populationQuery);
                FeatureQueryResult statesQueryResult = await statesTable.QueryFeaturesAsync(populationQuery);
                FeatureQueryResult countiesQueryResult = await countiesTable.QueryFeaturesAsync(populationQuery);

                // Display the selected cities in the graphics overlay.
                SimpleMarkerSymbol citySymbol = new SimpleMarkerSymbol(SimpleMarkerSymbolStyle.Circle, Color.Red, 16);
                foreach (Feature city in citiesQueryResult)
                {
                    Graphic cityGraphic = new Graphic(city.Geometry, citySymbol);

                    _selectedFeaturesOverlay.Graphics.Add(cityGraphic);
                }

                // Display the selected counties in the graphics overlay.
                SimpleLineSymbol countyLineSymbol = new SimpleLineSymbol(SimpleLineSymbolStyle.Dash, Color.Cyan, 2);
                SimpleFillSymbol countySymbol = new SimpleFillSymbol(SimpleFillSymbolStyle.DiagonalCross, Color.Cyan, countyLineSymbol);
                foreach (Feature county in countiesQueryResult)
                {
                    Graphic countyGraphic = new Graphic(county.Geometry, countySymbol);

                    _selectedFeaturesOverlay.Graphics.Add(countyGraphic);
                }

                // Display the selected states in the graphics overlay.
                SimpleLineSymbol stateLineSymbol = new SimpleLineSymbol(SimpleLineSymbolStyle.Solid, Color.DarkCyan, 6);
                SimpleFillSymbol stateSymbol = new SimpleFillSymbol(SimpleFillSymbolStyle.Null, Color.Cyan, stateLineSymbol);
                foreach (Feature state in statesQueryResult)
                {
                    Graphic stateGraphic = new Graphic(state.Geometry, stateSymbol);

                    _selectedFeaturesOverlay.Graphics.Add(stateGraphic);
                }
            }
            catch (Exception ex)
            {
                await new MessageDialog2(ex.ToString(), "Error").ShowAsync();
            }
        }
    }
}