Handling Appservice connections in a multiple instance of fulltrust process

Hello @DotNET Fan ,

This is my test code for your reference. I use WPF project as fulltrust process. Appservice can be used normally.

In WPF(.net 7.0),

 private AppServiceConnection connection = null;
 public MainWindow()
 {
     InitializeComponent();
     InitializeAppServiceConnection();
 }
 private async void InitializeAppServiceConnection()
 {
     connection = new AppServiceConnection();
     connection.AppServiceName = "SampleInteropService";
     connection.PackageFamilyName = Package.Current.Id.FamilyName;
     connection.RequestReceived += Connection_RequestReceived;
     connection.ServiceClosed += Connection_ServiceClosed;
     AppServiceConnectionStatus status = await connection.OpenAsync();
     if (status != AppServiceConnectionStatus.Success)
     {
         // something went wrong ...
         MessageBox.Show(status.ToString());
         this.IsEnabled = false;
     }
 }

Add Extensions in WAPP Package.appxmanifest.

   <Extensions>
     <desktop:Extension Category="windows.fullTrustProcess" 
                           Executable="WPFfulltrust\WPFfulltrust.exe"/>
     <uap:Extension Category="windows.appService">
        <uap:AppService Name="SampleInteropService" />
     </uap:Extension>
   </Extensions>  

In UWP App.xaml.cs, activate the UWP in the background and establish the AppServiceConnection.

 public static BackgroundTaskDeferral AppServiceDeferral = null;
 public static AppServiceConnection Connection = null;
 public static event EventHandler AppServiceDisconnected;
 public static event EventHandler<AppServiceTriggerDetails> AppServiceConnected;
 public static bool IsForeground = false;
 /// <summary>
 /// Initializes the singleton application object.  This is the first line of authored code
 /// executed, and as such is the logical equivalent of main() or WinMain().
 /// </summary>
 public App()
 {
     this.InitializeComponent();
     this.Suspending += OnSuspending;
     this.EnteredBackground += App_EnteredBackground;
     this.LeavingBackground += App_LeavingBackground;
 }
 private void App_LeavingBackground(object sender, LeavingBackgroundEventArgs e)
 {
     IsForeground = true;
 }
 private void App_EnteredBackground(object sender, EnteredBackgroundEventArgs e)
 {
     IsForeground = false;
 }
 protected override void OnBackgroundActivated(BackgroundActivatedEventArgs args)
 {
     base.OnBackgroundActivated(args);
     if (args.TaskInstance.TriggerDetails is AppServiceTriggerDetails details)
     {
         // only accept connections from callers in the same package
         if (details.CallerPackageFamilyName == Package.Current.Id.FamilyName)
         {
             // connection established from the fulltrust process
             AppServiceDeferral = args.TaskInstance.GetDeferral();
             args.TaskInstance.Canceled += OnTaskCanceled;
             Connection = details.AppServiceConnection;
             AppServiceConnected?.Invoke(this, args.TaskInstance.TriggerDetails as AppServiceTriggerDetails);
         }
     }
 }
 private void OnTaskCanceled(IBackgroundTaskInstance sender, BackgroundTaskCancellationReason reason)
 {
     AppServiceDeferral?.Complete();
     AppServiceDeferral = null;
     Connection = null;
     AppServiceDisconnected?.Invoke(this, null);
 }

In UWP MainPage, send message.

protected async override void OnNavigatedTo(NavigationEventArgs e)
{
    base.OnNavigatedTo(e);
    if (ApiInformation.IsApiContractPresent("Windows.ApplicationModel.FullTrustAppContract", 1, 0))
    {
        App.AppServiceConnected += MainPage_AppServiceConnected;
        App.AppServiceDisconnected += MainPage_AppServiceDisconnected;
        await FullTrustProcessLauncher.LaunchFullTrustProcessForCurrentAppAsync();
    }
}
/// <summary>
/// When the desktop process is connected, get ready to send/receive requests
/// </summary>
private async void MainPage_AppServiceConnected(object sender, AppServiceTriggerDetails e)
{
    App.Connection.RequestReceived += AppServiceConnection_RequestReceived;
    await Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
    {
        // enable UI to access  the connection
        btnRegKey.IsEnabled = true;
    });
}

 private async void btnClick_ReadKey(object sender, RoutedEventArgs e)
 {
     ValueSet request = new ValueSet();
     request.Add("KEY", tbKey.Text);
     AppServiceResponse response = await App.Connection.SendMessageAsync(request);
     // display the response key/value pairs
     tbResult.Text = "";
     foreach (string key in response.Message.Keys)
     {
         tbResult.Text += key + " = " + response.Message[key] + "\r\n";
     }
 }

This code refers to StefanWick's blog and code.

Feel free to comment on how there are other questions.

Thank you.

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