Event-based Asynchronous Pattern (EAP) Online

This sample demonstrates using the Event-based Asynchronous Pattern (EAP) for a QueryTask.

XAML

<UserControl x:Class="ArcGISWPFSDK.EventBasedAsync"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    xmlns:esri="http://schemas.esri.com/arcgis/client/2009">
    <Grid>
    <Grid.Resources>
        <esri:SimpleFillSymbol x:Key="RedFillSymbol"
                                   Fill="#66FF0000"
                                   BorderBrush="Red"
                                   BorderThickness="2" />
        <esri:SimpleRenderer x:Key="FillRenderer"
                                 Symbol="{StaticResource RedFillSymbol}" />
    </Grid.Resources>
        <esri:Map x:Name="MyMap" UseAcceleratedDisplay="True" WrapAround="True" Background="#FFE3E3E3">
            <esri:ArcGISTiledMapServiceLayer ID="MyLayer" 
                Url="http://services.arcgisonline.com/ArcGIS/rest/services/World_Street_Map/MapServer" />
            <esri:GraphicsLayer ID="MyGraphics"
                                Renderer="{StaticResource FillRenderer}"/>
    </esri:Map>
        <Border HorizontalAlignment="Right" VerticalAlignment="Top" Margin="0,10,131,0" Padding="5" Background="White" 
                BorderBrush="Black" BorderThickness="1" Width="231">
            <Border.Effect>
                <DropShadowEffect />
            </Border.Effect>
            <StackPanel Orientation="Horizontal" VerticalAlignment="Top" HorizontalAlignment="Left" 
                    Width="330" Height="50" Margin="5">
                <Button Content="QueryTask using Event Based Async" Margin="5" Width="196" Click="Button_Click_1" />       
            </StackPanel>
        </Border>
    </Grid>
</UserControl>

C#

using System.Windows.Controls;
using ESRI.ArcGIS.Client;
using ESRI.ArcGIS.Client.Tasks;
using System.Collections.Generic;
using System.Windows;

namespace ArcGISWPFSDK
{
    public partial class EventBasedAsync : UserControl
    {
        public EventBasedAsync()
        {
            InitializeComponent();
        }

        private void Button_Click_1(object sender, System.Windows.RoutedEventArgs e)
        {         
            ClearResults();
            QueryTask queryTask = new QueryTask("http://sampleserver6.arcgisonline.com/arcgis/rest/services/Census/MapServer/3");
            queryTask.ExecuteCompleted += QueryTask_ExecuteCompleted;
            queryTask.Failed += QueryTask_Failed;
            ESRI.ArcGIS.Client.Tasks.Query query = new ESRI.ArcGIS.Client.Tasks.Query();
            query.Where = "1=1";
            query.ReturnGeometry = true;
            query.OutSpatialReference = MyMap.SpatialReference;
            queryTask.ExecuteAsync(query, "initial");
        }

        // Explicit named event handles QueryTask Execute Completed Event.
        private void QueryTask_ExecuteCompleted(object sender, ESRI.ArcGIS.Client.Tasks.QueryEventArgs args)
        {
            FeatureSet featureSet = args.FeatureSet;
            AddResultsToMap(featureSet.Features);
        }

        // Explicit named event handles QueryTask Failed Event.
        private void QueryTask_Failed(object sender, TaskFailedEventArgs args)
        {
            MessageBox.Show("Query failed: " + args.Error);
        }

        private void ClearResults()
        {
           GraphicsLayer graphicsLayer = MyMap.Layers["MyGraphics"] as GraphicsLayer;
           graphicsLayer.Graphics.Clear();
        }

        private void AddResultsToMap(IList<Graphic> features)
        {
            GraphicsLayer graphicsLayer = MyMap.Layers["MyGraphics"] as GraphicsLayer;
            graphicsLayer.Graphics.AddRange(features);
            MyMap.ZoomTo(graphicsLayer.FullExtent);
        }
    }
}

VB.NET

Imports System.Windows.Controls
Imports ESRI.ArcGIS.Client
Imports ESRI.ArcGIS.Client.Tasks
Imports System.Collections.Generic
Imports System.Windows

Namespace ArcGISWPFSDK
    Partial Public Class EventBasedAsync
        Inherits UserControl
        Public Sub New()
            InitializeComponent()
        End Sub

        Private Sub Button_Click_1(sender As Object, e As System.Windows.RoutedEventArgs)
            UsingEventBased()
        End Sub

        Private Sub UsingEventBased()
            ClearResults()
            Dim t As New QueryTask("http://sampleserver6.arcgisonline.com/arcgis/rest/services/Census/MapServer/3")
            AddHandler t.ExecuteCompleted, AddressOf QueryTask_ExecuteCompleted
            AddHandler t.Failed, AddressOf QueryTask_Failed
            Dim query As New ESRI.ArcGIS.Client.Tasks.Query()
            query.Where = "1=1"
            query.ReturnGeometry = True
            query.OutSpatialReference = MyMap.SpatialReference
            t.ExecuteAsync(query, "initial")
        End Sub

        Private Sub QueryTask_ExecuteCompleted(sender As Object, args As ESRI.ArcGIS.Client.Tasks.QueryEventArgs)
            Dim featureSet As FeatureSet = args.FeatureSet
            AddResultsToMap(featureSet.Features)
        End Sub

        Private Sub QueryTask_Failed(sender As Object, args As TaskFailedEventArgs)
            MessageBox.Show("Query failed: " & Convert.ToString(args.[Error]))
        End Sub

        Private Sub ClearResults()
            Dim l = TryCast(MyMap.Layers("MyGraphics"), GraphicsLayer)
            l.Graphics.Clear()
        End Sub

        Private Sub AddResultsToMap(features As IList(Of Graphic))
            Dim l = TryCast(MyMap.Layers("MyGraphics"), GraphicsLayer)
            l.Graphics.AddRange(features)
            MyMap.ZoomTo(l.FullExtent)
        End Sub
    End Class
End Namespace