(ArcGIS Runtime SDK for .NET) Practice of the .NET API. Buffering and using geometry engine

Sample.cs

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 System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WpfApplication4
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        private static FeatureLayer m_layer { get; set; }
        private static FeatureLayer c_layer { get; set; }
        private static string item;
        
        public MainWindow()
        {
            InitializeComponent();

            MyMapView.Loaded += async (sender, e)=>{
                
                var map = new Map(Basemap.CreateLightGrayCanvas());
                MyMapView.Map = map;
                MyMapView.Map.OperationalLayers.Add(new FeatureLayer(new Uri("https://sampleserver6.arcgisonline.com/arcgis/rest/services/USA/MapServer/2")));

                m_layer = new FeatureLayer(new Uri("https://sampleserver6.arcgisonline.com/arcgis/rest/services/USA/MapServer/3"));
                c_layer = new FeatureLayer(new Uri("https://sampleserver6.arcgisonline.com/arcgis/rest/services/USA/MapServer/3"));
                await m_layer.LoadAsync();
                m_layer.IsVisible = false;
                c_layer.IsVisible = false;
                MyMapView.Map.OperationalLayers.Add(m_layer);
                MyMapView.Map.OperationalLayers.Add(c_layer);


                var stateQuery = new ServiceFeatureTable(new Uri("https://sampleserver6.arcgisonline.com/arcgis/rest/services/USA/MapServer/2"));
                await stateQuery.LoadAsync();
                var results = await stateQuery.QueryFeaturesAsync(new QueryParameters(){WhereClause = "1=1"});
                //var list = new List<String>();
                //foreach (var item in results)
                //{
                //    Debug.WriteLine(item.Attributes["state_name"]);
                //    list.Add(item.Attributes["state_name"].ToString());

                //}

                //cbxState.ItemsSource = list;
                var items = results.Select(f => f.Attributes["state_name"]).ToList();
                items.Sort();
                cbxState.ItemsSource = items;

                cbxState.SelectedIndex = 0;

                

            };

            

            cbxState.SelectionChanged += async (sender, e) =>
            {
                try
                {
                     item = (sender as ComboBox).SelectedItem.ToString();
                    m_layer.DefinitionExpression = string.Format("state_name = '{0}'", item);

                    var layer = MyMapView.Map.OperationalLayers[0] as FeatureLayer;
                    var state = await layer.FeatureTable.QueryFeaturesAsync(new QueryParameters { WhereClause = string.Format("state_name = '{0}'", item) });

                    var extent = state.FirstOrDefault().Geometry.Extent;
                    if (extent != null)
                        await MyMapView.SetViewpointAsync(new Viewpoint(extent));

                    var counties = await m_layer.FeatureTable.QueryFeaturesAsync(new QueryParameters() { WhereClause = "1=1" });
                    var itemsCounties = counties.Select(f => f.Attributes["name"]).ToList();
                    itemsCounties.Sort();
                    cbxCounty.ItemsSource = itemsCounties;

                    //cbxState.SelectedIndex = 0;



                    if (!m_layer.IsVisible)
                        m_layer.IsVisible = true;
                }
                catch (Exception ex)
                {
                    Debug.WriteLine(ex.Message);
                    //throw;
                }

                cbxCounty.SelectionChanged += (sender2, e2) =>
                {
                    var item2 = (sender2 as ComboBox).SelectedItem.ToString(); //Grab the selected item from the ComboBox
                    c_layer.DefinitionExpression = string.Format("name = '{0}'",item2);
                    var sfs = new SimpleFillSymbol(SimpleFillSymbolStyle.Solid, Colors.DodgerBlue, new SimpleLineSymbol(SimpleLineSymbolStyle.Solid, Colors.Red, 2));
                    var renderer = new SimpleRenderer(sfs);
                    c_layer.Renderer = renderer;

                    if (!c_layer.IsVisible)
                        c_layer.IsVisible = true;

                    //Call the buffer method on button click
                    btnBuffer.Click += (sender3, e3) =>
                    {
                        Buffer(item2);
                    };
                   
                    


                };
            };
        }

        async public static void Buffer (string itemGeo)
        {
            try
            {
                //Create the Query table
                var countyQuery = new ServiceFeatureTable(new Uri("https://sampleserver6.arcgisonline.com/arcgis/rest/services/USA/MapServer/3"));

                //Store the result of the Query in geometryResult
                var geometryResult = await countyQuery.QueryFeaturesAsync(new QueryParameters() { WhereClause = string.Format("name = '{0}'", itemGeo), ReturnGeometry = true });

                //Call GeometryEngine to buffer the geometry result by 2 meters
                var buffer = GeometryEngine.Buffer(geometryResult.FirstOrDefault().Geometry, 1);

                //Use the Difference tool to get the geometry of the (buffer - geometryResult)
                var cutBuffer = GeometryEngine.Difference(buffer, geometryResult.FirstOrDefault().Geometry);

                //Create a Simple Fill Symbol
                var symbol = new SimpleFillSymbol(SimpleFillSymbolStyle.Solid, Colors.Red, new SimpleLineSymbol(SimpleLineSymbolStyle.Solid, Colors.Black, 2));

                //Create a new graphic object with the cutBuffer and the symbol
                var graphic = new Graphic(cutBuffer, symbol);

                //Create a new Graphic Overlay
                GraphicsOverlay overlay = new GraphicsOverlay();

                //Add the graphic to the overlay 
                overlay.Graphics.Add(graphic);

                //Grab the window from the Application Namespace and cast it as MainWindow
                var window = (Application.Current.MainWindow) as MainWindow;

                //Reference the GraphicsOverlays to add the Overlay to the MapView
                window.MyMapView.GraphicsOverlays.Add(overlay);

                //Set the ViewPoint of the buffer extent
                if (buffer != null)
                    await window.MyMapView.SetViewpointAsync(new Viewpoint(buffer.Extent));

                //Referene the window instance to hook into the button click event
                window.btnClear.Click += (sender, e ) =>
                {
                    //overlay.IsVisible = false;
                    
                    
                };
                
                
            }
            catch (Exception ex)
            {
                Debug.WriteLine(ex.Message);
                //throw;
            }
           
        }
    }
}

Sample.xaml

<Window x:Class="WpfApplication4.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApplication4"
          xmlns:esri="http://schemas.esri.com/arcgis/runtime/2013" 
        mc:Ignorable="d"
        Title="MainWindow" Height="500" Width="700">

    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"/>
            <RowDefinition Height="125"/>
            <RowDefinition Height="40"/>
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition />
            <ColumnDefinition />
        </Grid.ColumnDefinitions>
        <Grid Grid.Row="1" Grid.ColumnSpan="2"> 
            <Grid.ColumnDefinitions>
                <ColumnDefinition />
                <ColumnDefinition />
                <ColumnDefinition />
                <ColumnDefinition />
            </Grid.ColumnDefinitions>
            <ComboBox  Grid.Column="1" x:Name="cbxState" Margin="10" />
            <ComboBox  Grid.Column="3" x:Name="cbxCounty" Margin="10" />
            <Label Grid.Column="0" Content="State" HorizontalAlignment="Center" VerticalAlignment="Center"></Label>
            <Label Grid.Column="2" Content="County" HorizontalAlignment="Center" VerticalAlignment="Center"></Label>
        </Grid>
        <esri:MapView Grid.ColumnSpan="4" x:Name="MyMapView"></esri:MapView>
        <Button x:Name="btnBuffer" Grid.Row="2" Grid.ColumnSpan="1" Content="Buffer"></Button>
        <Button x:Name="btnClear" Grid.Row="2" Grid.Column="2" Content="Clear Cut"></Button>
    </Grid>
</Window>