SharpGIS

#GIS from a .NET developer's perspective

Using Windows 10’s Extended Execution

Disclaimer: This article is written based on Windows 10 Tech Preview – Build 10041. Things might change completely in the future.

On Windows Phone Silverlight 8.0 it was possible to continue run an while the app wasn’t foregrounded. This was useful for Turn-by-turn or run-tracker type of apps. So even if you got a phone call or turned the screen off, the app would continue to run. Unfortunately that functionality was removed (well not removed, but rejected in certification) from Windows Phone Silverlight 8.1, and it was never added to Windows Runtime apps. That meant you were pretty much stuck on Silverlight 8.0 if you were building any of these apps.

However, in Windows 10 the functionality is finally here with the Windows Runtime! There’s not a lot of doc on it, and especially on phone it seems rather buggy, but I’ll try and explain the gist of it here.

First let’s create a new app, and add some basic location tracking to it.

private Geolocator locator;
private ObservableCollection<string> coordinates = new ObservableCollection<string>();
public MainPage()
{
    this.InitializeComponent();
    locator = new Geolocator();
    locator.DesiredAccuracy = PositionAccuracy.High;
    locator.DesiredAccuracyInMeters = 0;
    locator.MovementThreshold = 0;
    locator.PositionChanged += Locator_PositionChanged;
    coords.ItemsSource = coordinates;
}
 
private void Locator_PositionChanged(Geolocator sender, PositionChangedEventArgs args)
{
    var coord = args.Position;
    string position = string.Format("{0},{1}",
        args.Position.Coordinate.Point.Position.Latitude, //yeah it's this deep! Surprised smile
        args.Position.Coordinate.Point.Position.Longitude);
    var _ = Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
    {
        coordinates.Insert(0, position);
    });
}

And add the following ListView to the main page:

<ListView x:Name="coords" />

When you run this app, you’ll start seeing coordinates getting added to the list about once every second.

Now if you were to minimize the app (if you run as a desktop app – not a phone app), and return to the app, you might notice that the app still got coordinates added while it was minimized. That’s probably because you had the debugger attached. Try running the app without Visual Studio debugging, and you’ll notice the app will completely pause when it’s minimized. That means the app will stop tracking you if it’s not active. So first lesson: The Visual Studio debugger lies to you and prevents the app from suspending.

If we want to continue running the app while another app is active (or on a phone get an unexpected phone call), we now have a new “Extended Execution” session that we can start.

private ExtendedExecutionSession session;
 
private async void StartLocationExtensionSession()
{
   session = new ExtendedExecutionSession();
   session.Description = "Location Tracker";
   session.Reason = ExtendedExecutionReason.LocationTracking;
   session.Revoked += ExtendedExecutionSession_Revoked;
   var result = await session.RequestExtensionAsync();
   if (result == ExtendedExecutionResult.Denied)
   {
       //TODO: handle denied
   }
}

This tells the app that we’d like to continue even if the app is backgrounded. So you would usually call this API when you start running or doing your route.

Similarly we can stop the execution by disposing the session:

if (session != null)
{
    session.Dispose();
    session = null;
}

You would typically call this at the end of the run or when you reach your destination.

The only piece we’re missing is the Revoked event – I’m not entirely sure when this fires (there’s no documentation available yet), but on the Windows Phone emulator it fires the moment you leave the app, so I haven’t been able to get this working there.

private void ExtendedExecutionSession_Revoked(ExtendedExecutionSession sender, ExtensionRevokedEventArgs args)
{
    //TODO: clean up session data
    StopLocationExtensionSession();
}

Now add this to your app and call the StartLocationExtensionSession method and minimize your app. Wait a little and come back to it – note that points have been collected while the app wasn’t active. So now you can go write your run tracker app for Windows Desktop and take your desktop computer for a run… or wait for a Windows Phone 10 build where it’s working Smile

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