public sealed class Inventory : IBackgroundTask { 
   public void Run(IBackgroundTaskInstance taskInstance) { 
      
   } 
}

private async void OnRequestReceived(AppServiceConnection sender, 
   AppServiceRequestReceivedEventArgs args) {
      // Get a deferral because we use an awaitable API below to respond to the message 
}

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Text; 
using System.Threading.Tasks; 

using Windows.ApplicationModel.AppService; 
using Windows.ApplicationModel.Background; 
using Windows.Foundation.Collections;  

namespace MyAppService{
   public sealed class Inventory : IBackgroundTask { 
    
      private BackgroundTaskDeferral backgroundTaskDeferral; 
      private AppServiceConnection appServiceconnection; 
        
      private String[] inventoryItems = new string[] { "Robot vacuum", "Chair" }; 
      private double[] inventoryPrices = new double[] { 129.99, 88.99 };
        
      public void Run(IBackgroundTaskInstance taskInstance) {
         this.backgroundTaskDeferral = taskInstance.GetDeferral(); 
         taskInstance.Canceled += OnTaskCanceled;  
         var details = taskInstance.TriggerDetails as AppServiceTriggerDetails;
            
         appServiceconnection = details.AppServiceConnection;
         appServiceconnection.RequestReceived += OnRequestReceived; 
      } 
        
      private async void OnRequestReceived(AppServiceConnection sender,
         AppServiceRequestReceivedEventArgs args) {
        
            var messageDeferral = args.GetDeferral(); 
            ValueSet message = args.Request.Message; 
            ValueSet returnData = new ValueSet();  
                
            string command = message["Command"] as string; 
            int? inventoryIndex = message["ID"] as int?;  
            if (inventoryIndex.HasValue && 
                
            inventoryIndex.Value >= 0 && 
            inventoryIndex.Value < inventoryItems.GetLength(0)) {
         
               switch (command) {
            
                  case "Price": {
                     returnData.Add("Result", inventoryPrices[inventoryIndex.Value]); 
                     returnData.Add("Status", "OK"); 
                     break; 
                  } 
                    
                  case "Item": {
                     returnData.Add("Result", inventoryItems[inventoryIndex.Value]); 
                     returnData.Add("Status", "OK"); 
                     break; 
                  }  
                    
                  default: {
                     returnData.Add("Status", "Fail: unknown command"); 
                     break; 
                  }
               } else {
                  returnData.Add("Status", "Fail: Index out of range"); 
               } 
            }            
            await args.Request.SendResponseAsync(returnData); 
            messageDeferral.Complete(); 
      } 
        
      private void OnTaskCanceled(IBackgroundTaskInstance sender,
         BackgroundTaskCancellationReason reason){ 
            if (this.backgroundTaskDeferral != null) {
               // Complete the service deferral. 
               this.backgroundTaskDeferral.Complete(); 
            } 
      } 
   } 
}

using System; 

using Windows.ApplicationModel.AppService; 
using Windows.Foundation.Collections;
 
using Windows.UI.Xaml; 
using Windows.UI.Xaml.Controls;
  
// The Blank Page item template is documented at 
   http://go.microsoft.com/fwlink/?LinkId=402352&clcid=0x409  

namespace ClientApp {

   /// 
 
      /// An empty page that can be used on its own or navigated to within a Frame. 
   /// 
 
    
   public sealed partial class MainPage : Page {
   
      private AppServiceConnection inventoryService; 
      
      public MainPage() {
         this.InitializeComponent(); 
      } 
        
      private async void button_Click(object sender, RoutedEventArgs e){
      
         // Add the connection. 
         if (this.inventoryService == null) {
         
            this.inventoryService = new AppServiceConnection(); 
            this.inventoryService.AppServiceName = "com.microsoft.inventory"; 
            this.inventoryService.PackageFamilyName = 
               "bb1a8478-8005-46869923-e525ceaa26fc_4sz2ag3dcq60a"; 
                    
            var status = await this.inventoryService.OpenAsync();
                
            if (status != AppServiceConnectionStatus.Success) {
               button.Content = "Failed to connect"; 
               return; 
            } 
         } 
            
         // Call the service. 
         int idx = int.Parse(textBox.Text); 
         var message = new ValueSet(); 
            
         message.Add("Command", "Item"); 
         message.Add("ID", idx); 
            
         AppServiceResponse response = await 
            this.inventoryService.SendMessageAsync(message); 
         string result = ""; 
            
         if (response.Status == AppServiceResponseStatus.Success) { 
            // Get the data  that the service sent  to us. 
            if (response.Message["Status"] as string == "OK") {
               result = response.Message["Result"] as string; 
            } 
         } 
            
         message.Clear(); 
         message.Add("Command", "Price"); 
         message.Add("ID", idx); 
            
         response = await this.inventoryService.SendMessageAsync(message);
            
         if (response.Status == AppServiceResponseStatus.Success){
            // Get the data that the service sent to us. 
            if (response.Message["Status"] as string == "OK") {
               result += " : Price = " + "$"+ response.Message["Result"] as string; 
            } 
         }
            
         textBlock.Text = result;  
      } 
   } 
}