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I grew up in the nineties, that makes me awesome by default

Taking over MSDN BeLux

by Nico

The Belgian MSDN team started an initiative a few weeks ago. They give the password to the MSDNBeLux Twitter account to someone from the community, that person gets to tweet about his favorite Microsoft technology for an entire week.

This week it’s my turn, so if you follow the MSDN Belux Twitter account, expect to see some Windows Phone related tweets popping up!



Porting a real win8 app to WP8–part 3

by Nico

It’s been a good while since I last worked on porting Comic Cloud from Windows 8 to Windows Phone. If you can still remember, the goal was to maximize code reuse by using PCL wherever possible.

Part 3 will be the last part in this series, I’m currently holding a fully functional Windows Store app and a Windows Phone 8 app that can navigate pages and sent a search query to the api using a shared service layer. Theoretically everything is shared between the two platforms except the views, which makes sense. But it still required quite a lot of tinkering to get it to work.

PCL is improving

Microsoft is working hard on bringing as many libraries to PCL as they possibly can. In part 2 of the series I already mentioned the portable HttpClient, that library finally gave us a uniform way of doing HTTP requests on multiple platforms. Between part 2 and this part Microsoft has released the PCL version of their Azure Mobile Services SDK (beware! this one has breaking changes if you’re coming over from the platform specific SDK).

Changes in my project

I decided not to use the PCL version of WAMS yet because it has breaking changes and it doesn’t help me get rid of some platform specific projects, so no real use there yet.

What I wanted to achieve for demoing purpose was to get the search functionality working on the phone. The search function on the Windows Store app uses a BlockingCollection (MSDN link) This is a thread safe collection, meaning I can safely prefetch data from one thread while loading data on the other thread. My entire search service is relying on this class (it’s an implementation of the consumer/producer pattern by the way), only problem: Windows Phone doesn’t have the BlockingCollection class. So I could either abstract the search service, change it entirely or implement my own version of the BlockingCollection. The last option seemed like the hardest one to do so I went for it. I’m not entirely sure if I got the exact same functionality of the real BlockingCollection (it does lack some methods and properties, I only implemented what I needed for my app) but here it is

Code Snippet
  1. public class BlockingCollection<T> : Queue<T>
  2. {
  3.     private readonly object _locker = new object();
  4.     private readonly Queue<T> _itemQ;
  5.     private bool _canAddItems;
  7.     public BlockingCollection()
  8.     {
  9.         _itemQ = new Queue<T>();
  10.         _canAddItems = true;
  11.     }
  13.     public void EnqueueItem(T item)
  14.     {
  15.         lock (_locker)
  16.         {
  17.             _itemQ.Enqueue(item); // We must pulse because we're
  18.             Monitor.Pulse(_locker); // changing a blocking condition.
  19.         }
  20.     }
  22.     public bool TryTake(out T item, int millisecondsTimeout, CancellationToken cancellationToken)
  23.     {
  24.         cancellationToken.ThrowIfCancellationRequested();
  26.         if (_canAddItems)
  27.         {
  28.             lock (this)
  29.             {
  30.                 try
  31.                 {
  32.                     item = Dequeue();
  33.                     return true;
  34.                 }
  35.                 catch (Exception)
  36.                 {
  37.                     item = default(T);
  38.                     return false;
  39.                 }
  40.             }
  41.         }
  43.         item = default(T);
  44.         return false;
  45.     }
  47.     public bool TryAdd(T item, int millisecondsTimeout, CancellationToken cancellationToken)
  48.     {
  49.         cancellationToken.ThrowIfCancellationRequested();
  51.         if (_canAddItems)
  52.         {
  53.             lock (this)
  54.             {
  55.                 try
  56.                 {
  57.                     Enqueue(item);
  58.                     return true;
  59.                 }
  60.                 catch (Exception)
  61.                 {
  62.                     return false;
  63.                 }
  64.             }
  65.         }
  67.         return false;
  68.     }
  70.     public void CompleteAdding()
  71.     {
  72.         _canAddItems = false;
  73.     }
  74. }

It’s basically a Queue with some lock statements, it does work for me but I’m not responsible for any accidents that might occur Glimlach

Sharing ViewModels

All my viewmodels are in a PCL library, managed to get that to work in part 1. The ViewModelLocator can’t be made portable since some using statements are different and the WP8 version might need some other classes then the win8 version. I decided to add the Windows Store ViewModelLocator as a link into the Windows Phone 8 project, adding in some pre-processor directives made it work like a charm (I make this sound easy but it did take some time to get it just right).

Code Snippet
  1. using ComicDB.Framework;
  2. using ComicDB.SDKBroker;
  3. using ComicDB.View;
  4. using GalaSoft.MvvmLight;
  5. using GalaSoft.MvvmLight.Ioc;
  6. using Microsoft.Practices.ServiceLocation;
  9. using ComicDB.Framework.WinRT;
  10. using ComicDB.SDKBroker.WinRT;
  11. #else
  12. using ComicDB.Framework.WP8;
  13. using ComicDB.SDKBroker.WP8;
  14. #endif
  16. namespace ComicDB.ViewModel
  17. {
  18.     public class ViewModelLocator
  19.     {
  20.         public ViewModelLocator()
  21.         {
  22.             ServiceLocator.SetLocatorProvider(() => SimpleIoc.Default);
  24.             if (ViewModelBase.IsInDesignModeStatic)
  25.             {
  26.                 // Create design time view services and models
  27.                 //SimpleIoc.Default.Register<IDataService, DesignDataService>();
  28.             }
  29.             else
  30.             {
  31.                 // Create run time view services and models
  32. #if !WINDOWS_PHONE
  33.                 SimpleIoc.Default.Register<ComicDB.Framework.Interface.INavigationService, ComicDB.Framework.WinRT.NavigationService>();
  34. #else
  35.                 SimpleIoc.Default.Register<ComicDB.Framework.Interface.INavigationService, ComicDB.Framework.WP8.NavigationService>();
  36. #endif
  37.                 SimpleIoc.Default.Register<IService, Service>();
  38.                 SimpleIoc.Default.Register<IMessageApi, MessageApi>();
  39.                 SimpleIoc.Default.Register<IFrameworkApi, FrameworkApi>();
  40.                 SimpleIoc.Default.Register<IDispatcher, Dispatcher>();
  41.                 SimpleIoc.Default.Register<INetworkApi, NetworkApi>();
  42.             }
  44.             //register views
  45. #if !WINDOWS_PHONE
  46.             SimpleIoc.Default.Register<IMainPage, MainPage>();
  47.             SimpleIoc.Default.Register<IVolumeDetailPage, VolumeDetailPage>();
  48.             SimpleIoc.Default.Register<ICharacterDetailPage, CharacterDetailPage>();
  49.             SimpleIoc.Default.Register<ICollectionPage, CollectionPage>();
  50.             SimpleIoc.Default.Register<IDetailPage, DetailPage>();
  51.             SimpleIoc.Default.Register<IIssueDetailPage, IssueDetailPage>();
  52.             SimpleIoc.Default.Register<ILocationDetailPage, LocationDetailPage>();
  53.             SimpleIoc.Default.Register<INewsFeedPage, NewsFeedPage>();
  54.             SimpleIoc.Default.Register<IPersonDetailPage, PersonDetailPage>();
  55.             SimpleIoc.Default.Register<IStoryArcDetailPage, StoryArcDetailPage>();
  56.             SimpleIoc.Default.Register<ITeamDetailPage, TeamDetailPage>();
  57. #endif
  58.             //register viewmodels
  59.             SimpleIoc.Default.Register<MainViewModel>();
  60.             SimpleIoc.Default.Register<VolumeDetailViewModel>(true);
  61.             SimpleIoc.Default.Register<CharacterDetailViewModel>(true);
  62.             SimpleIoc.Default.Register<TeamDetailViewModel>(true);
  63.             SimpleIoc.Default.Register<IssueDetailViewModel>(true);
  64.             SimpleIoc.Default.Register<SearchViewModel>();
  65.             SimpleIoc.Default.Register<DetailViewModel>(true);
  66.             SimpleIoc.Default.Register<StoryArcDetailViewModel>(true);
  67.             SimpleIoc.Default.Register<LocationDetailViewModel>(true);
  68.             SimpleIoc.Default.Register<PersonDetailViewModel>(true);
  69.             SimpleIoc.Default.Register<CollectionViewModel>();
  70.             SimpleIoc.Default.Register<NewsFeedViewModel>(true);
  71.         }
  73.         public MainViewModel Main
  74.         {
  75.             get
  76.             {
  77.                 return ServiceLocator.Current.GetInstance<MainViewModel>();
  78.             }
  79.         }
  80.         //... all other VM properties follow here, left out for demo purpose

The pre-processor directives make the class look a bit dirty but it does get the job done.

At this point the WP8 app started and showed me the mainpage, with the mainviewmodel being its datacontext. Now I wanted to add an appbar with a searchbutton, a few problems there:

  • the default appbar is not bindable (solved with Cimbalino)
  • the mainviewmodel doesn’t have a command to navigate to the searchpage since Windows Store uses the Search charm

I decided to take the quick and dirty solution here so I added a normal appbar with a button and a navigation statement in code behind. The SearchPage has SearchViewModel as datacontext. In Windows Store it was normal for the SearchText property to be immediately holding a value since it came from the Search charm, not the case in WP8. Small change to the viewmodel so that it doesn’t fire its Search function when SearchText is empty or null. This was the result after all my hard work


Mission accomplished!


PCL still has a long way to go but it is improving, and for some cases it can actually already be very useful (for example to share model classes over different platforms).

I would however advice against going for maximum code reuse, it all sounds great but the reality is very different. I had to make a lot of decisions, change quite a lot of architecture and even add missing classes (like the BlockingCollection).

My advice if you want to build a multiplatform app: use PCL to share your model, maybe even some small framework with helper classes, but build a custom implementation of service layers and viewmodels for each platform, it will save you a lot of hassle and probably even time. If you do decide to go for maximum code reuse, make sure that you really really think about it when you design your architecture, make sure that every little thing has an abstraction better one interface too many than having to rewrite a class.

Here’s a comparing screenshot between the solution before and after adding the WP8 project and refactoring everything.


.Net | Devices | Metro | PCL | Patterns | WP8 | WinRT | Windows 8 | XAML

MSDN webcast SignalR and WP8 slides and demos

by Nico

I had the pleasure of presenting an MSDN webcast on SignalR and Windows Phone 8 yesterday. I had a great time presenting and believe it or not, all demos actually worked! (it was live coding)

The stream was recorded and will be available on Channel 9 soon, in the meantime you can download the demos here (the chat application in the download also has a Windows 8 client as an added bonus).

This slides are on SlideShare.


.Net | Community | MSDN | WP8 | signalr | Presenting

10 things you might have missed about MVVM Light

by Nico

Ever since I started playing with XAML based technologies (which actually isn’t that long ago) I’ve been looking into the MVVM (Model – View – ViewModel) pattern. I stumbled across MVVM Light pretty soon and liked the way it worked. Turns out I’m not the only one that likes it, there’s a whole set of developers, both hobby and professional, that really love this set of libraries. MVVM Light is, according to the author, not a framework but a set of libraries that take care of the plumbing to set up an MVVM structure and provide some extra helper classes to make life easier.

MVVM Light has changed a lot in its history, some elements were dragged out, others dragged in. Fact remains that it’s a fast, easy to use and lightweight framework. The author, Laurent Bugnion, does a great job of listening to the people that use MVVM Light, incorporating requested features and helping developers out. While talking to some of my fellow developers I’ve noticed a few times that there are certain elements of MVVM Light that others hadn’t heard of, and the same goes in the other direction. I’ve learned a lot of new things about MVVM Light just from talking with other users. Thinking about that gave me the idea of this blogpost and since those “10 things about…” posts seem to be popular, this was my chance. So here are my top 10 hidden gems of MVVM Light that you might have missed.

1. The MVVM Light installer

This one might seem a bit obvious, but in this NuGet driven world we would forget the added benefit of an installer. MVVM Light has an MSI installer that not only installs the binaries on your drive but it also provides project and itemtemplates in Visual Studio, along with a list of snippets. In case the Visual Studio 2012 update 2 removed your templates, reinstall the VSIX from C:\Program Files (x86)\Laurent Bugnion (GalaSoft)\Mvvm Light Toolkit\Vsix that should put the project templates back in place.

2. Constructor injection

This one is just awesome, and is actually a feature that can be found in most DI frameworks. MVVM Light uses SimpleIoc to register viewmodels and service classes at application launch (or during the app lifetime). Constructor injection means that you can specify a parameter in a class his constructor. When that class gets instantiated SimpleIoc will try to find a registered class of the same type as the parameter, when it finds one, that instance will get injected as the parameter of the constructor. Here’s an example, let’s say that in the ViewModelLocator, we register a navigation service.

Code Snippet
  1. SimpleIoc.Default.Register<INavigationService, NavigationService>();

We state here that we want to register an INavigationService in the IOC container, when it creates the instance we want it to be of type NavigationService. This “record” in the IOC container doesn’t have an instance yet, it gets instantiated when we fetch it from the container the first time. There are some occasions where you would want to create an instance of a class immediately when it gets registered. the Register<T> function of SimpleIoc has an overload to do just that.

Code Snippet
  1. SimpleIoc.Default.Register<INavigationService, NavigationService>(true);

Just pass in true as a parameter and it will create an instance right there and then.

Now we want to use the NavigationService in the MainViewModel.

Code Snippet
  1. ///<summary>
  2. /// Initializes a new instance of the MainViewModel class.
  3. ///</summary>
  4. public MainViewModel(INavigationService navigationService)
  5. {
  7. }

SimpleIoc will search for a registered class of type INavigationService and will inject it in this constructor. This saves us the hassle of manually contacting the IOC container and requesting the correct instance.

WARNING: do be careful with this, the order in which you register your classes with the IOC container can be important, especially when using the overload to create instances. If I would create the MainViewModel before the NavigationService is registered I would get a nullreference exception. So be aware of that.

3. SimpleIoc to simple? replace it!

The SimpleIoc library works great and is a cool, lightweight addition to MVVM Light, but it is actually really lightweight. It is a very realistic scenario that for larger apps the SimpleIoc just won’t do (or you’re like me and want to try out how hard it is to replace it with another one). In this example I’m going to replace SimpleIoc with AutoFac, another well known and very powerful IOC service.

First of all, we’re going to need the AutoFac libraries and the extra library that allows us to use the ServiceLocator, just like SimpleIoc does. So either from the package manager console or from the UI, add the CommonServiceLocator extra for AutoFac, the AutoFac libraries are a dependency so they’ll get installed as well. I’m using a brand new Windows Phone 8 project for this, started from the MVVM Light project template.

Code Snippet
  1. Install-Package Autofac.Extras.CommonServiceLocator

The only place we’ll need to change some code is in the ViewModelLocator.

This is the new ViewModelLocator constructor, I’ve put the old SimpleIoc code in comments so it’s easy to compare

Code Snippet
  1. static ViewModelLocator()
  2. {
  3.     var container = newContainerBuilder();
  5.     //ServiceLocator.SetLocatorProvider(() => SimpleIoc.Default);
  6.     ServiceLocator.SetLocatorProvider(() => newAutofacServiceLocator(container.Build()));
  8.     if (ViewModelBase.IsInDesignModeStatic)
  9.     {
  10.         //SimpleIoc.Default.Register<IDataService, Design.DesignDataService>();
  11.         container.RegisterType<Design.DesignDataService>().As<IDataService>();
  12.     }
  13.     else
  14.     {
  15.         //SimpleIoc.Default.Register<IDataService, DataService>();
  16.         container.RegisterType<DataService>().As<IDataService>();
  17.     }
  19.     //SimpleIoc.Default.Register<MainViewModel>();
  20.     container.RegisterType<MainViewModel>();
  21. }

And that’s it, we declare a ContainerBuilder, set it as the LocatorProvider. The container is then used to register everything we need. The SimpleIoc overload that creates an instance upon registering would look something like this in AutoFac.

Code Snippet
  1. container.RegisterInstance(newDataService()).As<IDataService>();

That’s it, constructor injection should still work exactly like before with SimpleIoc.

4. Built-in messages

MVVM Light has something called the messenger, it registers classes as listeners and can send messages to them. This is commonly used to do communication between viewmodels. Generally I would create a message class for each type of message that I want to send, but MVVM Light has some build in messages that we can use.

GenericMessage<T>(T content) A message that can contain whatever of type T.

Code Snippet
  1. Messenger.Default.Send(newGenericMessage<string>("my message"));
NotificationMessage(string notification)a message that contains a notification. this might be
used to send a notification to a notification factory that will show the message in the preferred way.
Code Snippet
  1. try
  2. {
  3.     //try something
  4. }
  5. catch (Exception ex)
  6. {
  7.     Messenger.Default.Send(newNotificationMessage(ex.Message));
  8. }

There’s also a NotificationMessage<T>(T notification) should you need it.

The next one is NotificationMessageAction(string notification, Action callback) basically the same as the NotificationMessage but you can add a callback action that will fire once the message is received. This one also has the generic implementation just like NotificationMessage.

DialogMessage(string content, Action<MessageBoxResult> callback) 
This message is meant to ask the user to input something and it will return the result of that input in the
MessageBoxResult. MessageBoxResult is an enum that lives in System.Windows
Code Snippet
  1. publicenumMessageBoxResult
  2. {
  3.   None = 0,
  4.   OK = 1,
  5.   Cancel = 2,
  6.   Yes = 6,
  7.   No = 7,
  8. }


Code Snippet
  1. Messenger.Default.Send(newDialogMessage("Are you sure?", result =>
  2.     {
  3.         if (result == MessageBoxResult.Yes)
  4.         {
  5.             //do something
  6.         }
  7.     }));

The DialogMessage class inherits from GenericMessage<string>

PropertyChangedMessage(T oldValue, T newValue, string propertyName)
The PropertyChangedMessage is meant to use like the RaisePropertyChanged implementation. This is great when multiple 
viewmodels need to respond to a changed property.
Code Snippet
  1. publicstring WelcomeTitle
  2. {
  3.     get
  4.     {
  5.         return _welcomeTitle;
  6.     }
  8.     set
  9.     {
  10.         if (_welcomeTitle == value)
  11.         {
  12.             return;
  13.         }
  15.         Messenger.Default.Send(newPropertyChangedMessage<string>(_welcomeTitle, value, "WelcomeTitle"));
  17.         _welcomeTitle = value;
  18.         RaisePropertyChanged(WelcomeTitlePropertyName);
  19.     }
  20. }

Be careful when registering listeners, try to use as many different types of messages as makes sense. You don’t want a wrong listener to receive a message because it happens to listen to the same type of message. To register a listener do this:

Code Snippet
  1. Messenger.Default.Register<PropertyChangedMessage<string>>(this, message =>
  2.     {
  3.         var a = message.NewValue;
  4.         //do something
  5.     } );

5. Portable libraries

MVVM Light is available on every XAML based platform. And it comes with a portable version now. The portable version is a separate library on NuGet.

Code Snippet
  1. Install-Package Portable.MvvmLightLibs

If you decide to use the portable version, make sure that every project in your solution that needs the MVVM Light libraries references the portable version. It does not work together with the “normal” MVVM Light libraries. When you use the PCL version, you can put your viewmodels in a separate, portable library and share them over, for example, a Windows Store and a Windows Phone app.

6. Event to Command behavior

MVVM Light has an ICommand implementation called RelayCommand that can be used to bind commands to actions. Like for example a button in XAML has a Command property that can be bound to an ICommand on its datacontext, so that when the button is clicked the ICommand will fire. Unfortunately not every XAML UI element has a bindable command property for every event that they can trigger and that’s where EventToCommand comes into play. With EventToCommand you can bind any event from a XAML UI element to an ICommand in the viewmodel.

First we’ll need two namespaces in our XAML page

Code Snippet
  1. xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
  2. xmlns:command="clr-namespace:GalaSoft.MvvmLight.Command;assembly=GalaSoft.MvvmLight.Extras.WP8"

Let’s say that we want to use the Tap event on a stackpanel.

Code Snippet
  1. <StackPanel Grid.Row="0" Orientation="Horizontal">
  2.     <i:Interaction.Triggers>
  3.         <i:EventTrigger EventName="Tap">
  4.             <command:EventToCommand Command="{Binding GoToCommand}" CommandParameter="Edit" />
  5.         </i:EventTrigger>
  6.     </i:Interaction.Triggers>

Line 3 specifies the event that we want to handle, note that this is a string so be aware of typos. Line 4 binds the actual command and can even pass a parameter to the ICommand implementation.

Code Snippet
  1. privateRelayCommand<string> _goToCommand;
  2. publicRelayCommand<string> GoToCommand
  3. {
  4.     get { return _goToCommand jQuery15206875578026641675_1366095632942 (_goToCommand = newRelayCommand<string>(NavigateAway)); }
  5. }

The NavigateAway method has this signature

Code Snippet
  1. privatevoid NavigateAway(string parameter)

The parameter will be the word “Edit” in this case as that’s what we’ve specified in the XAML. We can even pass the eventargs from the event to the Command by changing line 4 from the XAML snippet to this

Code Snippet
  1. <command:EventToCommand PassEventArgsToCommand="True" Command="{Binding GoToCommand}" />

Windows Store applications don’t have these behaviors out of the box so you won’t be able to use EventToCommand there unless you install the Win8nl toolkit from NuGet. Joost Van Schaik has build his own implementation of behaviors in WinRT and thanks to his efforts (and of some other people that have helped in the project) we can now use EventToCommand in WinRT.

7. DispatcherHelper

Since .net 4.5 we have the await/async keywords and being the good little citizens that we are we do a lot of stuff async now. That means if we want to update something that lives on the UI thread we’ll need the Dispatcher class to marshall our action to that thread. Normally we don’t have access to the Dispatcher from our viewmodel classes. MVVM Light contains a DispatcherHelper that will execute an action on the UI thread when needed.

Code Snippet
  1. DispatcherHelper.CheckBeginInvokeOnUI(() =>
  2.     {
  3.         //do something
  4.     });

The DispatcherHelper gets initialized in the App.xaml.cs in the InitializePhoneApplication method (in a WP8 project that is).

DispatcherHelper also has a RunAsync method. The difference with the CheckBeginInvokeOnUI is that the CheckBeginInvokeOnUI will first check if it’s already on the UI thread, if it is it will just execute the action, if it isn’t it will call the RunAsync method.

8. Blendable

MVVM Light has complete Blend support, meaning you can drag and drop properties from the viewmodel onto the view to generate a binding, or you can generate design time data based on the datacontext and so on. I’m really not that good in Blend so I’m not going into detail about this one, just remember that MVVM Light was build with Blend in mind.

9. Open Source

This one you probably knew but MVVM Light is completely open source. is the place to be if you want to dive into the source code.

10. Laurent is on Twitter and he’s a nice guy Glimlach

Laurent Bugnion, the founder of MVVM Light, is on Twitter! he’s a great guy to chat with and very eager to help out anyone who needs help.



MVVM Light is a great library with a few hidden gems. In this article I’ve discussed 8 very interesting ones that can make your life as a developer easier. I’ve included two more extra items because 10 is a prettier number than 8 Glimlach




.Net | MVVM Light | Windows 8 | WinRT | WP7 | WP8 | XAML

WP8, Leap Motion and a glue called Sockets

by Nico

I’m one of the lucky few who got their hands on a Leap Motion developer device (check out the video above if you’ve never heard of the Leap Motion). It’s a pretty cool device that gives you motion tracking not unlike Kinect but limited to finger and hand movement instead of complete body tracking.

I had the device and needed something to play with and what’s cooler then combining a cool gadget with an awesome smartphone? So I decided to build a small proof-of-concept that would capture finger movement in a WPF application and translate that movement to a moving ellipse in a Windows Phone application.

The Leap Motion’s documentation got me to a moving ellipse in a WPF application pretty fast thanks to the samples and documentation found on their developer portal. It took me a bit more time to get the position of the ellipse send to the phone, I wanted to use Sockets for this (SignalR would be way easier but I didn’t want an extra service running, now I have peer to peer communication).

Here’s how I did it

WPF and the Leap Motion

First, the WPF project. This project will be the socket server and the app that captures the Leap Motion’s output. The application only has one page with this as XAML

Code Snippet
  1. <Window x:Class="LeapWpPoc.MainWindow"
  2.         xmlns=""
  3.         xmlns:x=""
  4.         Title="MainWindow"
  5.         Width="525"
  6.         Height="350">
  7.     <Canvas x:Name="TheCanvas">
  8.         <Ellipse x:Name="TheEllipse"
  9.                  Canvas.Left="211"
  10.                  Canvas.Top="118"
  11.                  Width="70"
  12.                  Height="70"
  13.                  Fill="#FFFF0C00"
  14.                  Stroke="Black" />
  15.         <TextBlock x:Name="TextBlockStatus"
  16.                    Canvas.Left="10"
  17.                    Canvas.Top="10"
  18.                    Foreground="Red"
  19.                    Text="Not connected"
  20.                    TextWrapping="Wrap" />
  21.     </Canvas>
  22. </Window>

Let’s have a look at how to interact with the Leap Motion first.

First thing you need when working with the Leap Motion (apart from the actual device that is) is a reference to LeapCSharp.NET4.0.dll however, you’ll also need Leap.dll and LeapCSharp.dll. Now I find this a bit dirty and I sincerely hope that the Leap Motion team will find a way to fix this but those two libraries aren’t referencable in our project but they need to be present in the application’s directory or it won’t work. What I did is add them as an existing item to the project, set their build action to Content and Copy if newer, at least this way they will always get copied into the build directory of the application.

Next, you’ll needs a class that inherits from Listener (Listener is part of the Leap Motion SDK). Listener is a base class that provides a bunch of virtual methods like OnExit, OnDisconnect, OnConnect and OnFrame. Feel free to override those to add some logging or logic but I’m only using the OnFrame method here. Here’s my Listener class

Code Snippet
  1. class PocListener : Listener
  2. {
  3.     public event EventHandler<FrameDetectedEventArgs> FrameDetected;
  5.     public override void OnFrame (Controller controller)
  6.     {
  7.         // Get the most recent frame and report some basic information
  8.         Frame frame = controller.Frame ();
  10.         if (FrameDetected != null)
  11.         {
  12.             FrameDetected(this, new FrameDetectedEventArgs(frame));
  13.         }
  14.     }
  15. }

The OnFrame method fires constantly, passing all the movement information, if any, in a frame. If my listener implementation detects a frame the FrameDetected event will fire, passing in the detected frame as an eventarg, FrameDetectedEventArgs is a very basic class that only passes the frame data to whoever is listening to the event.

Code Snippet
  1. public class FrameDetectedEventArgs : EventArgs
  2. {
  3.     public Frame Frame { get; set; }
  5.     public FrameDetectedEventArgs(Frame frame)
  6.     {
  7.         Frame = frame;
  8.     }
  9. }

Notice that the OnFrame method needs a Controller as parameter? Controller is the class from the Leap Motion API that talks to the device. I create a new instance of Controller and my Listener in the MainWindow constructor.

Code Snippet
  1. private Frame _previousFrame;
  2. private Frame _currenFrame;
  3. private readonly PocListener _listener;
  4. private readonly Controller _controller;
  5. private readonly SocketFactory _socketFactory;
  7. public MainWindow()
  8. {
  9.     InitializeComponent();
  11.     _listener = new PocListener();
  12.     _controller = new Controller();
  14.     // Have the sample listener receive events from the controller
  15.     _controller.AddListener(_listener);
  17.     _listener.FrameDetected += ListenerOnFrameDetected;
  18. }

This is the constructor and some private fields, I need to keep track of both the current frame and the previous one to detect if there’s any change in the position of the hand or fingers. I also have an instance of PocListener (my own Listener class) and of Controller, both get instantiated in the constructor.Next I need to register my Listener in the Controller, that’s done on line 14 and then finally I attach an event handler to the FrameDetected event.

The event handler of the FrameDetected event will be responsible of checking if hands and fingers are detected.

Code Snippet
  1. private void ListenerOnFrameDetected(object sender, FrameDetectedEventArgs frameDetectedEventArgs)
  2. {
  3.     _currenFrame = frameDetectedEventArgs.Frame;
  5.     if (!_currenFrame.Hands.Empty)
  6.     {
  7.         // Get the first hand
  8.         Hand hand = _currenFrame.Hands[0];
  10.         // Check if the hand has any fingers
  11.         FingerList fingers = hand.Fingers;
  12.         if (!fingers.Empty)
  13.         {
  14.             if (_previousFrame == null) _previousFrame = _currenFrame;
  15.             //check if the current frame is different from the last frame
  16.             if (_currenFrame != _previousFrame)
  17.             {
  18.                 //we only need one finger so we'll take the first one that's detected
  19.                 Finger finger = fingers[0];
  21.                 float x = _previousFrame.Fingers[0].TipPosition.x - finger.TipPosition.x;
  22.                 float y = _previousFrame.Fingers[0].TipPosition.y - finger.TipPosition.y;
  24.                 //update the sphere's position
  25.                 Dispatcher.BeginInvoke((Action)(() =>
  26.                                                 {
  27.                                                     Canvas.SetTop(TheEllipse, Canvas.GetTop(TheEllipse) + y);
  28.                                                     Canvas.SetLeft(TheEllipse, Canvas.GetLeft(TheEllipse) - x);
  29.                                                 }));
  31.                 //set this frame as the previous one and get ready to receive a new frame
  32.                 _previousFrame = _currenFrame;
  33.             }
  34.         }
  35.     }
  36. }

First we check if the previous frame has the same information as the current frame, if it does there’s no need to update the ellipse’s position.

If a hand and fingers are detected I select the first detected finger, because that’s currently the only one I’m interested in. Since all the Leap Motion actions are happening on a separate thread I need to invoke the UI thread to update the ellipse’s position, that’s what’s happening on line 25. The position of a UIElement in a Canvas in XAML is set through attached properties (Canvas.Left=”177” for example) to set these in code we use Canvas.SetLeft. To determine the new location of the ellipse I take the X and Y positions of the first finger in the previous frame and substract the X and Y of the first finger in the current frame. The new Y value gets added to the Canvas.Top of the ellipse and the new X value gets subtracted  from the Canvas.Left value. Last but not least I set the previousframe to the currentframe.

That’s all the code you need to get an ellipse moving in a canvas with the Leap Motion. So part 1 is a great success. Now onto the bigger challenge, getting a similar ellipse to move in a Windows Phone project.

Windows Phone and sockets

Implementing sockets to make devices talk to each other over the wire can be challenging but it’s also very rewarding and just plain fun once it works. I haven’t worked with sockets before so I had a real blast trying to figure this out and I went through the roof once that ellipse started moving on the Windows Phone emulator Glimlach. Before we dive into the sockets, let’s have a quick look at the MainPage.

Code Snippet
  1. <Canvas x:Name="TheCanvas">
  2.     <Ellipse x:Name="TheEllipse"
  3.              Canvas.Left="302"
  4.              Canvas.Top="186"
  5.              Width="70"
  6.              Height="70"
  7.              Fill="#FFFF0C00"
  8.              Stroke="Black" />
  9.     <TextBlock x:Name="TextBlockStatus"
  10.                Canvas.Left="10"
  11.                Canvas.Top="10"
  12.                Foreground="Red"
  13.                Text="Not connected"
  14.                TextWrapping="Wrap" />
  15. </Canvas>

Exactly the same controls as in the WPF project, nothing spectacular here. Let’s have a look at the code behind the MainPage.

Code Snippet
  1. public partial class MainPage
  2. {
  3.     private SocketClient _client;
  4.     const int Port = 8000;
  5.     private const string IpAddress = "";
  7.     // Constructor
  8.     public MainPage()
  9.     {
  10.         InitializeComponent();
  11.         _client = new SocketClient();
  13.         _client.OnConnected += (sender, args) => Dispatcher.BeginInvoke(() =>
  14.             {
  15.                 TextBlockStatus.Text = "Connected";
  16.                 TextBlockStatus.Foreground = new SolidColorBrush(Colors.Green);
  17.             });
  18.         _client.OnMessageReceived += (sender, args) => Dispatcher.BeginInvoke(() => MoveBall(args.Response));
  19.         _client.Connect(IpAddress, Port);
  21.         _client.Receive();
  22.     }
  24.     private void MoveBall(string response)
  25.     {
  26.         response = response.Replace(',', '.');
  27.         var coordinates = response.Split(';');
  29.         float y = float.Parse(coordinates[0]);
  30.         float x = float.Parse(coordinates[1]);
  32.         Canvas.SetTop(TheEllipse, y);
  33.         Canvas.SetLeft(TheEllipse, x);
  34.     }
  35. }

First some fields, don’t worry about the SocketClient class, we’ll get to that in a minute. Some constants holding the IP address and the port of the server (don’t forget to change this IP address to the address of your own pc!)

In the constructor we instantiate the SocketClient instance and handle its two events. The OnConnected event is going to change the text of the TextBlock to “Connected” and the OnMessageReceived event handler will move the ellipse.

The MoveBall() method will do the actual moving. The message that we will receive will be a string that has the Y and X of the ellipse in the WPF application seperated by a semicolon. The problem I had here was that instead of a dot to separate the decimals .NET had changed it into a comma (which is the default decimal sign in Belgium) so I need to change that back. I then split up the string using the semicolon as split character, parse the values into a float and set the ellipse to its new position. Let’s get serious and dive into the socket stuff now.

Sockets provide us with TCP and UDP communication, next to a whole bunch of other features. This app will use a TCP connection between WPF and a Windows Phone application. Since we’re currently looking at the Windows Phone app, let’s continue there. I’ve added a class called SocketClient that takes care of connection a socket, sending and receiving messages. Let’s start with the fields and constructor.

Code Snippet
  1. // Cached Socket object that will be used by each call for the lifetime of this class
  2. Socket _socket;
  4. // Signaling object used to notify when an asynchronous operation is completed
  5. static ManualResetEvent _clientDone;
  7. // Define a timeout in milliseconds for each asynchronous call. If a response is not received within this
  8. // timeout period, the call is aborted.
  9. const int TimeoutMilliseconds = 5000;
  11. // The maximum size of the data buffer to use with the asynchronous socket methods
  12. const int MaxBufferSize = 2048;
  14. public event EventHandler<MessageReceivedEventArgs> OnMessageReceived;
  15. public event EventHandler OnConnected;
  17. public SocketClient()
  18. {
  19.     _clientDone = new ManualResetEvent(false);
  20. }

First field is the actual socket that we’ll be using, second one is a reset event that we can use to make a thread block while waiting for an event to fire. The timeout is the max amount of time that the reset event will block a thread. The buffersize is the size of the buffer for socket messages. The two events are fired when the app receives a socket message or when a socket connects.

The most important function of the SocketClient class that I’m building here is to connect two sockets.

Code Snippet
  1. public string Connect(string hostName, int portNumber)
  2. {
  3.     string result = string.Empty;
  5.     // Create DnsEndPoint. The hostName and port are passed in to this method.
  6.     DnsEndPoint hostEntry = new DnsEndPoint(hostName, portNumber);
  8.     // Create a stream-based, TCP socket using the InterNetwork Address Family.
  9.     _socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
  11.     // Create a SocketAsyncEventArgs object to be used in the connection request
  12.     SocketAsyncEventArgs socketEventArg = new SocketAsyncEventArgs {RemoteEndPoint = hostEntry};
  14.     socketEventArg.Completed += (sender, args) =>
  15.                                         {
  16.                                             // Retrieve the result of this request
  17.                                             result = args.SocketError.ToString();
  19.                                             // Signal that the request is complete, unblocking the UI thread
  20.                                             _clientDone.Set();
  22.                                             if (OnConnected == null) return;
  24.                                             OnConnected(this, new EventArgs());
  25.                                         };
  27.     // Sets the state of the event to nonsignaled, causing threads to block
  28.     _clientDone.Reset();
  30.     // Make an asynchronous Connect request over the socket
  31.     _socket.ConnectAsync(socketEventArg);
  33.     // Block the UI thread for a maximum of TIMEOUT_MILLISECONDS milliseconds.
  34.     // If no response comes back within this time then proceed
  35.     _clientDone.WaitOne(TimeoutMilliseconds);
  37.     return result;
  38. }

The connect method takes in two parameters, the hostname (or IP address) and the portnumber of the socket we want to connect to. Based on these two parameters we create a DnsEndPoint that will be passed to the server socket as being the remote endpoint so that the server socket knows where to send his messages. Next we instantiate the Socket, stating that it’s using an internal IPv4 network, a stream socket and the TCP protocol. Now that we have a socket and an endpoint we’ll need some eventargs, those args will be passed onto the server. Once the connection succeeds (or fails) the Completed event on the SocketAsyncEventArgs will fire, in that event handler we’ll trigger the OnConnected event. With that in place we call the Reset() method on the ManualResetEvent to set the event to nonsignaled, call the ConnectAsync() method on the Socket and pass in the eventargs and finally blocking the thread for a certain time to allow the socket time to connect.

So now that our client can connect to a socket, let’s build something to send messages to the connected socket. From the Windows Phone 8 version it looks like this

Code Snippet
  1. public void Send(string data)
  2. {
  3.     data = data + "<EOF>";
  5.     if (_socket != null)
  6.     {
  7.         SocketAsyncEventArgs socketEventArg = new SocketAsyncEventArgs
  8.             {
  9.                 RemoteEndPoint = _socket.RemoteEndPoint,
  10.                 UserToken = null
  11.             };
  13.         socketEventArg.Completed += (sender, args) =>
  14.                                         {
  15.                                             _clientDone.Set();
  16.                                         };
  18.         // Add the data to be sent into the buffer
  19.         byte[] payload = Encoding.UTF8.GetBytes(data);
  20.         socketEventArg.SetBuffer(payload, 0, payload.Length);
  22.         // Sets the state of the event to nonsignaled, causing threads to block
  23.         _clientDone.Reset();
  25.         // Make an asynchronous Send request over the socket
  26.         _socket.SendAsync(socketEventArg);
  28.         // Block the UI thread for a maximum of TIMEOUT_MILLISECONDS milliseconds.
  29.         // If no response comes back within this time then proceed
  30.         _clientDone.WaitOne(TimeoutMilliseconds);
  31.     }
  32. }

We get in the message as a parameter, at the end of the message I add “<EOF>” just to make sure that I only get the part that I need at the server side and that the message has been delivered in full. If at this point the socket is null then it isn’t connected yet. If it isn’t we once again instantiate SocketAsyncEventArgs. The data gets serialized into a byte array and set as a buffer in the eventargs. Set the ManualResetEvent to nonsignaled, start sending the message over the socket async and block the thread.

And last but not least there’s the code to receive messages on the socket.

Code Snippet
  1. public void Receive()
  2. {
  3.     if (_socket != null)
  4.     {
  5.         SocketAsyncEventArgs socketEventArg = new SocketAsyncEventArgs
  6.             {
  7.                 RemoteEndPoint = _socket.RemoteEndPoint
  8.             };
  10.         // Setup the buffer to receive the data
  11.         socketEventArg.SetBuffer(new Byte[MaxBufferSize], 0, MaxBufferSize);
  13.         socketEventArg.Completed += (sender, args) =>
  14.             {
  15.                 if (args.SocketError == SocketError.Success)
  16.                 {
  17.                     // Retrieve the data from the buffer
  18.                     string response = Encoding.UTF8.GetString(args.Buffer, args.Offset, args.BytesTransferred);
  19.                     response = response.Trim('\0');
  21.                     if (response.Contains("<EOF>"))
  22.                     {
  23.                         response = response.Substring(0, response.IndexOf("<EOF>"));
  24.                         if (OnMessageReceived != null)
  25.                             OnMessageReceived(this, new MessageReceivedEventArgs(response));
  26.                     }
  28.                     Receive();
  29.                 }
  31.                 _clientDone.Set();
  32.             };
  34.         // Sets the state of the event to nonsignaled, causing threads to block
  35.         _clientDone.Reset();
  37.         // Make an asynchronous Receive request over the socket
  38.         _socket.ReceiveAsync(socketEventArg);
  40.         // Block the UI thread for a maximum of TIMEOUT_MILLISECONDS milliseconds.
  41.         // If no response comes back within this time then proceed
  42.         _clientDone.WaitOne(TimeoutMilliseconds);
  43.     }
  44. }

So the same story with the null check on the socket and creating of the SocketEventArgs. Once the Completed event fires we’ll check if the receive was successful  and if the received message contains “<EOF>”, if it does we take everything before <EOF> and pass it in the MessageReceivedEventArgs that go with the MessageReceived event.

Code Snippet
  1. public class MessageReceivedEventArgs : EventArgs
  2. {
  3.     public string Response { get; set; }
  5.     public MessageReceivedEventArgs(string response)
  6.     {
  7.         Response = response;
  8.     }
  9. }

Once everthing is handled we call the Receive method again so it’s ready to start receiving the next message.

And that’s basically all the logic for a socket connection on the Windows Phone side of things. The only thing left to do in the app is change the MainPage’s constructor to initialize the SocketClient and add some fields.

Code Snippet
  1. private SocketClient _client;
  2. const int Port = 8000;
  3. private const string IpAddress = "";
  5. // Constructor
  6. public MainPage()
  7. {
  8.     InitializeComponent();
  9.     _client = new SocketClient();
  11.     _client.OnConnected += (sender, args) => Dispatcher.BeginInvoke(() =>
  12.         {
  13.             TextBlockStatus.Text = "Connected";
  14.             TextBlockStatus.Foreground = new SolidColorBrush(Colors.Green);
  15.         });
  16.     _client.OnMessageReceived += (sender, args) => Dispatcher.BeginInvoke(() => MoveBall(args.Response));
  17.     _client.Connect(IpAddress, Port);
  19.     _client.Receive();
  20. }

The constructor instantiates the SocketClient, attaches an handler to the OnConnected event to update the textbox with the connection status and handle the OnMessageReceived event to update the position of the ellipse. Don’t forget to update the IP address to the one from your own pc!

Back to WPF!

Now that our Windows Phone app is ready, it’s time to implement the socket server. As mentioned before, the WPF app that gets input from the Leap Motion will serve as socket server.

I’ve added a class to the WPF project called SocketFactory, it serves the same function as the SocketClient class in the Windows Phone project but from a server point of view. The way to build and use a socket in full blown .net 4.5 differs a bit from how we did it in Windows Phone. First we’ll need a state class, this contains a socket, the buffersize, a byte array to function as the buffer and a stringbuilder to recompose the message.

Code Snippet
  1. // State object for reading client data asynchronously
  2. public class StateObject
  3. {
  4.     // Client  socket.
  5.     public Socket WorkSocket = null;
  6.     // Size of receive buffer.
  7.     public const int BufferSize = 1024;
  8.     // Receive buffer.
  9.     public byte[] Buffer = new byte[BufferSize];
  10.     // Received data string.
  11.     public StringBuilder Sb = new StringBuilder();
  12. }

Next, we’ll need some fields in the SocketFactory class

Code Snippet
  1. // Thread signal.
  2. public static ManualResetEvent AllDone = new ManualResetEvent(false);
  3. private StateObject _state;
  4. public event EventHandler OnConnected;

And here’s the function to receive a connection request

Code Snippet
  1. public void Start()
  2. {
  3.     IPHostEntry ipHostInfo = Dns.GetHostEntry(Dns.GetHostName());
  4.     IPAddress ipAddress = ipHostInfo.AddressList[3];
  5.     IPEndPoint localEndPoint = new IPEndPoint(ipAddress, 8000);
  7.     Socket listener = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
  9.     // Bind the socket to the local endpoint and listen for incoming connections.
  10.     try
  11.     {
  12.         listener.Bind(localEndPoint);
  13.         listener.Listen(100);
  15.         while (true)
  16.         {
  17.             // Set the event to nonsignaled state.
  18.             AllDone.Reset();
  20.             // Start an asynchronous socket to listen for connections.
  21.             Console.WriteLine("Waiting for a connection...");
  22.             listener.BeginAccept(AcceptCallback, listener);
  24.             // Wait until a connection is made before continuing.
  25.             AllDone.WaitOne();
  27.             if (OnConnected == null) return;
  29.             OnConnected(this, new EventArgs());
  30.         }
  32.     }
  33.     catch (Exception e)
  34.     {
  35.         Console.WriteLine(e.ToString());
  36.     }
  37. }

We declare a socket called listener, pass it the same parameters as we did for Windows Phone, stating that it’s local network, streaming and using the TCP protocol. We need to bind this socket to an IPEndPoint, to create an IPEndPoint we need an IPAddress and a port. Lines 3 and 4 are used to getting the computer’s IP address from its hostname. Once we have that we can bind the socket to the endpoint. Make sure that the port you set here is the same port you try to connect to in the Windows Phone app. Once the socket connects the callback fires, in the callback we start receiving data from the connected client.

Code Snippet
  1. public void AcceptCallback(IAsyncResult ar)
  2. {
  3.     // Signal the main thread to continue.
  4.     AllDone.Set();
  6.     // Get the socket that handles the client request.
  7.     Socket listener = (Socket)ar.AsyncState;
  8.     Socket handler = listener.EndAccept(ar);
  10.     // Create the state object.
  11.     _state = new StateObject { WorkSocket = handler };
  13.     handler.BeginReceive(_state.Buffer, 0, StateObject.BufferSize, 0, ReadCallback, _state);
  14. }

Once data is received, the ReadCallback fires

Code Snippet
  1. public void ReadCallback(IAsyncResult ar)
  2. {
  3.     StateObject state = (StateObject)ar.AsyncState;
  4.     Socket handler = state.WorkSocket;
  6.     int bytesRead = handler.EndReceive(ar);
  8.     if (bytesRead > 0)
  9.     {
  10.         // There  might be more data, so store the data received so far.
  11.         state.Sb.Append(Encoding.ASCII.GetString(
  12.             state.Buffer, 0, bytesRead));
  14.         // Check for end-of-file tag. If it is not there, read
  15.         // more data.
  16.         string content = state.Sb.ToString();
  17.         if (content.IndexOf("<EOF>") > -1)
  18.         {
  19.             Console.WriteLine("Read {0} bytes from socket. \n Data : {1}",
  20.                 content.Length, content);
  21.         }
  22.         else
  23.         {
  24.             // Not all data received. Get more.
  25.             handler.BeginReceive(state.Buffer, 0, StateObject.BufferSize, 0, ReadCallback, state);
  26.         }
  27.     }
  28. }

We can get the stateobject and socket from the IAsyncResult and we start reading until we encounter “<EOF>”, once everything is received we write it out in the output window. Now in this example the server won’t actually be receiving any messages, I’ve just put in this method in case you want to enhance it or have some use for the code.

What is important in this sample is the Send method, this will send a message over the connected socket to the client.

Code Snippet
  1. public void Send(string data)
  2. {
  3.     Send(_state.WorkSocket, data);
  4. }
  6. private void Send(Socket handler, string data)
  7. {
  8.     data = data + "<EOF>";
  9.     // Convert the string data to byte data using ASCII encoding.
  10.     byte[] byteData = Encoding.ASCII.GetBytes(data);
  12.     // Begin sending the data to the remote device.
  13.     handler.BeginSend(byteData, 0, byteData.Length, 0, SendCallback, handler);
  14. }

I’ve split up the Send into two methods, the public one just receives the message we want to send and passes it trough to the private one, also passing in the socket to use. This way the application itself doesn’t need to worry about selecting a socket, let the socketFactory deal with that. The Send method adds the end of file part to the message, serializes it into a byte array and sends it over the socket. Once the send is complete, the callback will fire.

Code Snippet
  1. private void SendCallback(IAsyncResult ar)
  2. {
  3.     try
  4.     {
  5.         // Retrieve the socket from the state object.
  6.         Socket handler = (Socket)ar.AsyncState;
  8.         handler.EndSend(ar);
  9.     }
  10.     catch (Exception e)
  11.     {
  12.         Console.WriteLine(e.ToString());
  13.     }
  14. }

I’m not really doing anything in the callback, but this would be the perfect place to check for successful delivery and maybe notifying the UI thread to show a confirmation or something similar.

Now that our socket infrastructure is in place and we have a client updating a UI based on the received messages, it’s time to finish this sample by letting the server send the coordinates of the ellipse. In the MainWindow add a field for the socket factory. (line 5 is the extra field)

Code Snippet
  1. private Frame _previousFrame;
  2. private Frame _currenFrame;
  3. private readonly PocListener _listener;
  4. private readonly Controller _controller;
  5. private readonly SocketFactory _socketFactory;

With the new field in place, replace (or update) the constructor to this

Code Snippet
  1. public MainWindow()
  2. {
  3.     InitializeComponent();
  5.     _socketFactory = new SocketFactory();
  6.     _socketFactory.OnConnected += (sender, args) => Dispatcher.BeginInvoke((Action) (() =>
  7.         {
  8.             TextBlockStatus.Text = "Connected";
  9.             TextBlockStatus.Foreground = new SolidColorBrush(Colors.Green);
  10.         }));
  12.     Task.Run(() => _socketFactory.Start());
  14.     _listener = new PocListener();
  15.     _controller = new Controller();
  17.     // Have the sample listener receive events from the controller
  18.     _controller.AddListener(_listener);
  20.     _listener.FrameDetected += ListenerOnFrameDetected;
  22.     Timer timer = new Timer(200);
  23.     timer.Elapsed += (sender, args) => Dispatcher.BeginInvoke((Action)(() =>
  24.         _socketFactory.Send(string.Format("{0};{1}", Canvas.GetTop(TheEllipse), Canvas.GetLeft(TheEllipse)))));
  26.     timer.Start();
  27. }

We instantiate the SocketFactory, attach an handler for the OnConnected event to update the UI. The SocketFactory’s Start method is queued on the thread pool to run async, this way the UI thread will remain responsive. The Leap Motion get’s initialized and we start a timer. This timer will make sure that every 200 milliseconds the coordinates of the ellipse are send over the socket to the client. The sending of the message needs to be done on the UI thread because we need the ellipse’s coordinates, and that ellipse lives on the UI thread.

Now, why use a timer? In the first version of this sample a message was send every time the ellipse moved, this resulted in really really really poor performance, messages were being send faster than they arrived causing all kinds of weird behavior. Sending it every 200 milliseconds makes it move quite well.

Everything is in place now, so run it and move the ellipse around with the Leap Motion!


In this post I’ve explained my adventure of connecting the Leap Motion to a Windows Phone application by using sockets. While not the easiest thing to set up or use, sockets are a really powerful way of communicating between applications no matter what platform they’re on (as long as that platform supports sockets).

The Leap Motion is a great device. It’s small, light, has a very small footprint on your system and is just plain fun to mess around with. I could’ve used anything for a socket example but making something move on screen, on two devices at the same time by just moving your hand has something magically. The Leap Motion is definitely on my list of awesome gadgets.

The code for this post can be found on my Skydrive


NUI | LeapMotion | .Net | Devices | WP8 | WPF

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About the author


My name is Nico, I’m an MVP Windows Platform Development living in Belgium.
I’m currently employed as a .NET consultant at RealDolmen, one of Belgium’s leading IT single source providers.

I'm also founding member and board member of the Belgian Metro App Developer Network, a user group focussed on Windows 8 and Windows Phone development. If you're in Belgium feel free to drop by if we're doing an event.

Since June 2012 I'm a proud member of Microsoft's Extended Experts Team Belgium. And in February 2013 I became a member of DZone's Most Valuable Bloggers family.

In 2013 I became a book author and wrote "Windows 8 app projects, XAML & C# edition".

In 2014 I received the MVP award for the very first time.

I hope to get feedback from my readers either through comments, mail (, twitter, facebook, …












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