Calling an App Service from a WPF/WinForms Win32 App

I just put up a new sample at https://github.com/arunjeetsingh/SampleCode/tree/master/Win32AppServiceClient. My apologies to all the folks who have been waiting for this sample. I know I promised I’d put up this sample during my Build talk. Well, here it is now. Better late than never right! Who uses this feature? Well, the brand new Outlook 2016 desktop app uses it to talk to Cortana so you’re in good company. Before I dive any deeper into the sample I do want to point out a couple of important limitations of app services when they are called from a Win32 process:

1. The calling app must be running as the currently logged on user.
2. When the calling app is a Win32 app the app service background task can not run longer than 30 seconds.

The sample demonstrates a Windows Presentation Foundation (WPF) app calling a universal app service. App services are a new feature of universal Windows 10 apps that allow an app to provide services to other apps. These services can be accessed by other apps as well as Win32 apps such as WPF or WinForms apps.

This sample demonstrates how a WPF app can call into an app service. To run the sample you will need Visual Studio 2015 and the Windows SDK. Both of these can be found at http://developer.windows.com.

With Visual Studio, open the solution Win32AppServiceClient.sln. There are three projects in this solution:

• RandomNumberService – This project is a Windows Runtime component. It contains the code for the background task that implements the app service we use for the sample. RandomNumberGeneratorTask.cs contains the background task class. The background tasks’ main entrypoint is the Run method. In this method, the RandomNumberGeneratorTask sets itself up with a deferral so it can stay running and provide the app service. It also uses the incoming AppServiceTriggerDetails to attach an event handler to the AppServiceTriggerDetails.RequestReceived event. This enables the RandomNumberGeneratprTask to respond to requests from the app service client. The OnRequestReceived handler simply parses the input for minimum and maximum integer values. It then generates a random number between those values and returns it.
• AppServicesProvider – AppServicesProvider is the universal Windows app that contains RandomNumberService. The AppServicesProvider project contains a reference to RandomNumberService. The Package.appxmanifest file in AppServicesProvider also contains a windows.appService extension. This is how the AppServicesProvider app exposes the RandomNumberService to other apps. In the Package.appxmanifest’s uap:Extension element the EntryPoint attribute represents the type name of the background task providing the app service. The Name attribute in the uap:AppService element represents the name of the app service.
• Win32AppServiceClient – The Win32AppServicesClient is a WPF application. The project file of this WPF application (Win32AppServiceClient.csproj) has been modified to include references to the universal Windows 10 APIs. This enables us to use the Windows.ApplicationModel.AppService.AppServiceConnection class that lets an app connect to an app service. The MainWindow.xaml page of Win32AppServiceClient does exactly that. It presents the user the option to provide minimum and maximum integer values. The Click handler of the Generate Random Number button then calls the random number service exposed by AppServicesProvider with these values. The result is then displayed on screen.

Feel free to submit pull requests on this README.md or the code if you think it could use improvement. Happy hacking!

@aruntalkstech