Andrej Tozon's blog

In the Attic


Reactive Extensions #3: Windows Phone 7

Following the theme from my previous two posts, this post will be about using Reactive Extensions on Windows Phone 7. I'll use a similar scenario as before – gradually load a few tiles into an ItemsControl. Let’s get started.

Starting a project

Create a new “Windows Phone Application”. Add references to assemblies Microsoft.Phone.Reactive and System.Observable to add support for Rx, then Microsoft.Phone.Controls.Toolkit (found in Silverlight Toolkit for Windows Phone 7) and System.Windows.Interactivity (Expression Blend for Windows Phone 7 SDK, should be already installed if you installed WP7 tools / Expresion Blend 4 SP1).


Put a ListBox on the main, name it list and possibly change the control to an ItemsControl (we don’t need to select items).

<Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0">
    <ItemsControl Name="list" />

Create the ItemTemplate:

<DataTemplate x:Key="TileTemplate">
    <Grid Width="142"
          Background="{StaticResource PhoneAccentBrush}"
        <TextBlock Text="{Binding}"
                   FontSize="{StaticResource PhoneFontSizeExtraExtraLarge}"
                   Foreground="{StaticResource PhoneForegroundBrush}"
                   Margin="20,0,0,10" />

… use WrapPanel for the ItemsPanel:

<ItemsPanelTemplate x:Key="WrapItemsPanelTemplate">
    <toolkit:WrapPanel />

… and update the ItemsControl to use them:

<ItemsControl Name="list" 
              ItemTemplate="{StaticResource TileTemplate}"
              ItemsPanel="{StaticResource WrapItemsPanelTemplate}" />

Reactive Extensions

I copied the code from my previous post:

public partial class MainPage : PhoneApplicationPage
    public MainPage()

        Loaded += OnLoaded;

    private readonly string text = "reactive wp7";

    private void OnLoaded(object sender, RoutedEventArgs e)

    private void AddLetter(char letter)

Animating on appearance

Instead of using layout states as in Silverlight version (they are not supported in WP7’s ListBox), I was back on using a behavior to trigger the entrance animation:

public class LoadedBehavior : Behavior<FrameworkElement>
    protected override void OnAttached()
        AssociatedObject.Loaded += AssociatedObject_Loaded;

    void AssociatedObject_Loaded(object sender, System.Windows.RoutedEventArgs e)

    private Storyboard CreateStoryboard()
        Storyboard sb = new Storyboard();
        DoubleAnimation animation = new DoubleAnimation
            Duration = TimeSpan.FromMilliseconds(1000),
            From = -90,
            To = 0,
            EasingFunction = new CubicEase { EasingMode = EasingMode.EaseOut }
        Storyboard.SetTargetProperty(animation, new PropertyPath("(UIElement.Projection).(PlaneProjection.RotationY)"));


        animation = new DoubleAnimation
            Duration = TimeSpan.FromMilliseconds(1000),
            From = 0,
            To = 1,
            EasingFunction =
                new CubicEase() { EasingMode = EasingMode.EaseOut }
        Storyboard.SetTargetProperty(animation, new PropertyPath(UIElement.OpacityProperty));

        Storyboard.SetTarget(sb, AssociatedObject);
        return sb;

Wrapping up

The last thing to do was adding the behavior to the ItemTemplate and prettify the layout a bit.

That’s it, pretty easy – tiled letters are now gradually filling up the space on the main page, each letter appearing on the screen with a subtle animation. For more details on how that works check out my previous posts on Reactive Extensions.

The demo project can be downloaded from here. In the future I’ll look into using more Reactive Extensions on Windows Phone 7 – stay tuned.


Lost in time? Zip it!

In my last blog post I wrote about using Reactive Extensions together with layout states in Silverlight to gradually introduce collections of data to a ListBoxes. One small problem with code from that post is that I’m generating the sequence of data myself, whereas in real-world scenario would be pulling it from some data source like database or web service. It’s easy to turn an existing collection to an Observable by using the ToObservable() operator, but the generated sequence wouldn’t be time-based, as it would have been if we had used the GenerateWithTime() constructor.

So how do we turn an existing enumerable collection into a time-based observable sequence?

First, we need to convert the enumerable to a plain observable. Here’s the example of such conversion:

private readonly string text = "REACTIVE";

IObservable<char> letters = text.ToObservable();

[Reminder: a string is a collection/sequence of chars – turning this collection into an observable sequence results in IObservable<char>]

Next, we need to create an observable sequence that will serve as a “beat” – a time-based sequence that would define points in time at which we want to “release” (or trigger) the next item in our data collection. The following code will create a fast “beat”, “thumping” at every 300 ms:

IObservable<long> beat = Observable.Interval(TimeSpan.FromSeconds(.3));

Now we only need to lay the numbers from the enumerable collection over created beat and for that, there is a convenient combinator operator available in Reactive Extensions. It’s called – Zip.

IObservable<string> dancingLetters = numbers.Zip(beat, (letter, time) => letter);

Zip operator will take two observable sequences (letters and beat) and produce a new value pair when a new value is present in both sequences, kind of like a zipper. In our case, the letters sequence starts with 8 values and beat starts with zero. As the beat sequence starts producing new values (one every 0.3 seconds), these new values are paired (zipped) with values from letters, resulting in a new pair of data (letter, time) releasing every 0.3 seconds. As we’re only interested in numbers from the numbers sequence, we return only those values, ignoring values values from the beat sequence (=> letter).

dancingLetters is now a time-based observable sequence which we can subscribe to:


… and get the same result as in previous post, only with letters.

One great thing about Reactive Extensions is they are very extensible, meaning you can write your own operators by creating new extension methods. For frequent operations like the one we’ve just performed, it’s a perfect fit. Here’s an example of an OnTimeline() operator that would put an observable sequence on a live timeline:

public static class ObservableEx
    public static IObservable<TSource> OnTimeline<TSource>(this IObservable<TSource> source, TimeSpan period)
        return source.Zip(Observable.Interval(period), (d, t) => d);

With the new operator handy and in place, we could rewrite the previous snippet as (full code ahead):

private readonly string text = "REACTIVE";

private void OnLoaded(object sender, RoutedEventArgs e)

private void AddLetter(char letter)

This application in action can be observed through this link


In this post, I extended the code sample from previous post by creating a new extension method that puts an existing observable sequence on a timeline, with delayed item notification.

Download source code from here.

Silverlight Layout States with Reactive Extensions

I’ve been working on several applications where I needed to display several items in a ListBox (or an ItemsControl) at startup, but they had to appear on the screen one by one, with a short delay, not all at once. Using ListBoxItem’s layout states took care of handling how an individual item would appear in the list, but I still needed to handle a short pause between each item being added to the list. Usually I resorted to using a Timer, which sorted out that needed delay for me, but that really felt like hacking that had nothing to do with the real problem.

Reactive Extensions, however, offer a much elegant solution. The GenerateFromTime() construction operator is a close relative to the Generate() operator used in my previous blog entry, except GenerateFromTime() adds an important time dimension to generated sequence – the last parameter in this operator lets you specify a delay between each call to OnNext():

private readonly IObservable<string> numbers = Observable.GenerateWithTime(1, i => i <= 8, i => i + 1, i => i.ToString(), i => TimeSpan.FromSeconds(.3));

The above code snippet will produce an observable sequence of 8 strings, progressing through these strings with a 0.3 seconds delay.

The rest of the code:

private void OnLoaded(object sender, RoutedEventArgs e)

private void AddImage(string image)

Note the ObserveOnDispatcher() operator again – GenerateWithTime uses a timer operating on a background thread so we need to ensure the AddImage() method is called on the UI thread.

Layout states for this sample are kept really basic:

<VisualStateGroup x:Name="LayoutStates">
        <VisualTransition GeneratedDuration="0:0:1">
                <CubicEase EasingMode="EaseOut"/>
    <VisualState x:Name="AfterLoaded"/>
    <VisualState x:Name="BeforeLoaded">
            <DoubleAnimation Duration="0" To="-94" Storyboard.TargetProperty="(UIElement.Projection).(PlaneProjection.RotationY)" Storyboard.TargetName="grid" d:IsOptimized="True"/>
            <DoubleAnimation Duration="0" To="0" Storyboard.TargetProperty="(UIElement.Opacity)" Storyboard.TargetName="grid" d:IsOptimized="True"/>
    <VisualState x:Name="BeforeUnloaded"/>

And the final result can be observed by following this link.image

This post has shown how to use Reactive Extensions in Silverlight to gradually fill a ListBox, with a bonus of a nice item entry animation, provided by the layout states.

Download source code from here.

Reactive Extensions – from pull to push: where’s the block?

I’ve discussed Reactive Extensions with a few people after my Rx talk last week and thought I’d clear up some confusion by clarifying on this blog…

One thing to know about Reactive Extensions is that simply going from pull model (enumerating) to push model (observing) doesn’t give you immediate background thread processing – everything is still happening on the same thread.

For example, let’s look at the following code and put a few debugger breakpoints in it:


Right at the top, there’s an array of image names I’m adding to the ListBox (AddImage() method). In this WPF app, the OnLoaded() method handles the Loaded event, where foreach loop iterates through the array and calls the AddImage() method.

Red balls indicate the places where I’d put the breakpoints, and the number in it tells the order in which they would be hit. Following the track, it is obvious that the OnLoaded() method is blocking until all images in the array is added into the ListBox.

To transform this code to use the observer/pull model, the following changes are made:

  1. The array (now an IObservable<string>) is generated with the Generate() Observable constructor.
  2. foreach loop is removed from the OnLoaded() method and replaced with the Observable subscription, providing the methods for OnNext and OnCompleted.

The Subscribe() method looks harmless sitting alone on now shortened OnLoaded() method, but guess what – it’s still blocking it! Take a look at the execution path: the code would enter the method, and upon subscription, starts calling the AddImage() method. After that, it calls OnCompleted() and then, only then, continues the execution in the OnLoaded() method and finally exits.

The thing to be careful about here is the fact that even if the images.Subscribe() method looks innocent and instant, it may be executing a long(er) time, if an observable sequence is very long. Which also means that the current thread will be blocked for that time also. And we don’t want the UI thread blocked.


What we can do to achieve the behavior we want and expected (not blocking the UI) is forcing subscription on a new – background – thread and expect the observable to call us back on the UI thread. Note that the AddImage() method has to be called on the UI thread because the code accesses the ListBox and if called from a non-UI thread, the call would fail. The code below exercises these changes and results in a whole different flow: upon subscription, the UI thread exits the OnLoaded() method immediately, while the subscription processing is done in a new thread. ObserveOnDispatcher() operator ensures that for each element in the observable sequence, AddImage() method is safely called on the UI thread.


Bleeding Edge 2010: Reactive Extensions Slides and Demo

These are slides and demo from my talk on Reactive Extensions from Thursday’s Bleeding Edge conference:

Slides | Demo code

Thanks to all for attending the talk.

What's Wrong with *my* WCF Service?

While I was watching the Silverlight TV episode on common WCF service issues with Silverlight (Silverlight TV 46: What's Wrong with my WCF Service?) I remembered one more issue that bit my neck a while back and thought it was worth pointing it out again... It was one of those “Service returned ‘Not found’” issues, except nothing I would do seemed to help solving it.

My simple WCF service was returning an IEnumerable<T> and I was using a Linq query for filtering the results before returning them to the client. Can you guess where I’m going to?

Let’s step back and take a look at the symptoms I was facing: the original problem was that service call returned with the infamous “NotFound” exception.

I would try using Client Http Stack to get more info about the exception – nothing. Reverted to Browser Http Stack and implemented service stack to return Faults – still nothing. I wrapped my service method call into a try…catch statement inside service method – no errors would’ve been caught on the server side and the NotFound error would persist… Furthermore, stepping through the service code didn’t throw any exceptions and the error only happened when service call returned one or more records. When there was zero, it returned fine… Hmmm… Something happening on the wire? Fiddler wasn’t much of a help either.

What helped at last was a careful examination of the service method call. Facepalm! I was failing in materializing the Linq query by not forcing its evaluation with the .ToList() extension method (or similar) and data never made it to the other side.

Lesson learned – when your services return IEnumerable and you’re using Linq to query/transform data double check that you’re returning something that client would actually have a chance enumerating.

Watch Silverlight TV videos, pinned to full screen

One of the “annoyances” with Silverlight (and similar browser plugins) is with watching a video in a multi-monitor set up – you would pop out your Silverlight video player to full screen on one monitor and continue working on your other monitor – which would cause your video player to return to its normal size, ruining your watching experience. Well, that was the case until Silverlight 4 came out. Silverlight 4 supports “full-screen pinning” in a way that you can choose the Silverlight 4 app to remain pinned to full screen on one monitor even if you focus your work on the other.

Unfortunately, (the regular) Channel 9 still doesn’t use Silverlight 4 which means you don’t get this option of full-screen pinning, but guess what – Channel 9 is in a process of refurbishing and a preview of the new site is available at the This is good news for us because they’re using Silverlight 4 for their player, which basically means you can watch your Silverlight TV full-screen pinned simply by prefixing Silverlight TV show’s URL with the word preview. For example, show 40: You Are Already a Windows Phone Developer is available on

However, there seems to be a lag with publishing new content, resulting in shows not being available on the preview site at the same time as on the regular time. At the time of this writing, it appears that Show 40 is the last one available on the preview site, with shows 41 and 42 remaining on the regular site only. Anyway, it’s good to see Channel 9 going Silverlight 4 – hope to the new site up and running soon.

Microsoft Silverlight 4 Data and Service Cookbook [Review]

It’s been a while since Silverlight 4 was released by Microsoft and while we’re patiently waiting for a few other books to be released, I would definitely recommend the "Microsoft Silverlight 4 Data and Service Cookbook” by Gill Cleeren and Kevin Dockx. It’s not an advanced book on Silverlight, nor is it a reference book, it’s compilation of useful, hands-on recipes to get you started on data scenarios using Silverlight 4. If you’re new to Silverlight, you’ll definitely appreciate the way this book is written: a short description of a problem will guide you through the provided code example and explanation of what and why, usually followed by the “There’s more…” section - and that’s the part that will be appreciated even by more advanced Silverlight developers, as it would reveal some hidden tricks and not-so-known secrets of Silverlight framework’s workings. As scenarios go, those seem to cover basic to intermediate type of problems, with advanced problems left out, which is kind of understandable, but at certain points in the book I still wished the authors would write more about an alternative implementation(s) of a solution, or point me to some (online) resource for further reading.

The book covers Silverlight data scenarios, starting with the essentials like Data Binding, moving its way through explaining the data controls and finally settle on explaining the ways Silverlight could talk to the data server through various services. Special chapters are dedicated to WCF RIA Services and converting existing applications to use Silverlight, the latter explaining a few of Microsoft technologies and APIs that are not directly associated to Silverlight, but which Silverlight applications could benefit a lot from by using them.

If you’re new to Silverlight and want to develop Line-of-Business applications, this book is definitely for you as it will get you started immediately and give you enough information to build on the provided code examples for yourself. If you’re an advanced Silverlight user, I think there are some high points in this book that will gain you additional knowledge on the subject, but be prepared to read a lot of code/XAML listings which you probably already know how they work and the problems they solve.

All in all, the “Microsoft Silverlight 4 Data and Service Cookbook” is a great Silverlight book to have – it’s available in print or digital edition (plus all code examples are available for download).

My NTK10 slide decks

Another NTK has ended, and in my opinion, this year’s conference was one of the greatest and most enjoyable for the past few years. This is a list of sessions I had (alone or with co-speakers), along with the PowerPoint slide decks (all in Slovenian Language):

Silverlight and MEF

[The Photo Gallery application I was showing is available on the CodePlex and will be updated with the latest bits shortly]

ASP.NET, WebForms, Silverlight – What to choose?

Having @dusanzu as a co-host, this was a Birds of Feather (BoF) session. And although not listed as such, it turned out great anyway. There wasn’t much slides since this was a discussion – the slide-deck will be available from the NTK site.

Silverlight and WCF RIA Services

[I built a basic NTK schedule viewer app from the scratch, using Silverlight Business project template and showing off different features of RIA Services in the process. If somebody is interested in seeing the code that was produced on the talk, please contact me]

Tips & Tricks: Expression Blend for Developers

Again, we (@krofdrakula and I) wanted to show as much useful information and show designer-developer workflow, so we concentrated on showing off Visual Studio, Expression Blend (through Team Foundation Server running in a cloud), and the result was only a two-slide PowerPoint slide-deck (which will be available for download from the NTK site as well). As it turned out, even those two slides were way too much for what we wanted to share in a 45-minute time slot.

What’s new in Silverlight 4?

[The source code accompanying this slide-deck is way overdue for publishing – stay tuned for my future blog posts, where I’ll cover all the features I put together in my Silverlight 4 demo app]

A big thanks to all that attended my talks, I hope to hear from you in the near future. Another big thanks goes to local Microsoft office, for organizing another great event.

Oh, and another thing – this year’s NTK conference was covered through twitter as well (significantly better than last year, but still, plenty of room to improve for the next year). I’ll sign off with the snapshot of Twedge, a Silverlight 4 widget, finding its way to the CodePlex later this week. To see it in action, visit http:/


See you next year!

NT Konferenca 2010 – Where you’ll find me

This year’s NT Konferenca is starting next week! Organized by local Microsoft, it will be held (for the 15th year in a row!) in beautiful Portoroz (Slovenia), that’s now become a traditional venue for this event. Over 130 sessions, labs and seminars will be delivered by over 130 speakers in only four days – that’s a lot of content.

I’ll be speaking (and discusing things) on the following conference sessions:

Tuesday, 25th

10:15 – 11:30 Silverlight and MEF
11:45 – 12:30 ASP.NET, WebForms, Silverlight – What to choose? [BoF session, co-hosting with @dusanzu]

Wednesday, 26th

10:15 – 11:30 Silverlight and WCF RIA Services
11:45 – 12:30 Tips & Tricks: Expression Blend For Developers [Tips & Tricks session, co-presenting with @krofdrakula]
13:30 – 14:15 What’s new in Silverlight 4?
16:30 – 17:30 MVP Panel [A panel discussion with all Slovenian MVPs]

See any theme/pattern here? ;)

You can follow me and my whereabouts next week through twitter [@andrejt], with the official conference hashtag being #ntk10.

See you next week…