Andrej Tozon's blog

In the Attic


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…

Named & optional parameters in Silverlight 4

Named & optional parameters are a new C# language feature coming up with .NET FX 4.0 and guess what… it’s in Silverlight 4 as well!

Optional parameters will come very useful when defining complex APIs where you would usually have to provide several overloads for the same method for it to make sense to wide variety of usages. Let’s take a look at this basic example:

public void PositionWindow(bool isTopMost, double left = 0, double top = 0, double width = 800, double height = 600)
    Window window = Application.Current.MainWindow;
    window.TopMost = isTopMost;
    window.Left = left;
    window.Top = top;
    window.Width = width;
    window.Height = height;

isTopMost is the only parameter that’s required, all other parameter specify their default value, which makes them optional. Needless to say, the default values will be used for those parameters which the calling function doesn’t provide. One thing to know is that optional parameter must always be declared after required parameters.

The following calls are all valid:

PositionWindow(true); // position and size set to defaults
PositionWindow(true, 100); // top position and size set to defaults
PositionWindow(true, 100, 200); // sizes set to defaults
PositionWindow(true, 100, 200, 600, 200); // all parameters provided

But what if you wanted to provide the size only and leave the position to be set to defaults? Enter named parameters. The same method above can be called also with:

PositionWindow(isTopMost:true, width: 600, height: 200); // named parameters
PositionWindow(true, width: 600, height: 200); // naming is optional when positioned right
PositionWindow(true, height: 200, width: 600); // order doesn't matter
PositionWindow(height: 200, width: 600, isTopMost: true); // ... even with the required parameters

Simple, eh? The need for named and optional parameters may have come from the need to simplify COM automation, but they may prove just as useful in many other cases. But before you go start creating methods with tens of optional parameters, note that this is not the ultimate solution, and one thing worth noting is although the calls above look like they are passing the specified parameters only, the compiler in fact generates them with all parameters in place. This is how the Reflector sees that last batch of calls:

bool CS$0$0000 = true;
double CS$0$0001 = 600.0;
double CS$0$0002 = 200.0;
this.PositionWindow(CS$0$0000, 0.0, 0.0, CS$0$0001, CS$0$0002);
CS$0$0001 = 600.0;
CS$0$0002 = 200.0;
this.PositionWindow(true, 0.0, 0.0, CS$0$0001, CS$0$0002);
CS$0$0001 = 200.0;
CS$0$0002 = 600.0;
this.PositionWindow(true, 0.0, 0.0, CS$0$0002, CS$0$0001);
CS$0$0001 = 200.0;
CS$0$0002 = 600.0;
CS$0$0000 = true;
this.PositionWindow(CS$0$0000, 0.0, 0.0, CS$0$0002, CS$0$0001);

Potential architectural issues aside, I’m quite happy to see this feature come to Silverlight as well. How about you?

Putting Silverlight tweets on the map

Twitter Maps application was updated last night to allow embedding custom Twitter maps on web sites. The process of creating a custom Twitter map is fairly easy, these are the steps for creating a Silverlight tweets map.

1. Go to the Bing Maps site, click on the MAP APPS button and select the Twitter Maps application:


The Twitter Maps application will open, showing you the location of the most recent tweets in your area. Of course, only geotagged tweets will be shown on the map.

2. Click on the plus sign on the left side to open the Search Filters panel:


3. Type “silverlight” into the keywords field and click Submit:


4. Click the Embed in your site button, found at the bottom of the left column:


… and the embedding dialog window will show up.

5. Select Anywhere for the Map Location and check that the Current Filters is set to “silverlight”:

image6. Copy the provided HTML code into your site.

And this is how this Silverlight tweets map looks like:

Using different filters and settings will get you a whole lot of alternatives for creating your own Twitter map. With geotagging getting more popular by the day, your maps will be getting richer along the ride.

Add version 4 components to your Silverlight 3 application with MEF

Note: this post and accompanying source code was updated to reflect the latest MEF build on Codeplex. This build is much more aligned with the version of MEF that is available from Silverlight 4 Beta SDK.

The current Silverlight version is v3, with v4 in the making (in Beta 1 at the time of this posting). Silverlight 4 is bringing a lot of new features in the core framework and to use them, you would have to migrate your applications to the latest version, once it gets released. And that would require all the potential users to upgrade their machines to the latest version as well.

But there’s another way. By using MEF (Managed Extensibility Framework), you can extend your existing Silverlight 3 application with optional package, which would contain Silverlight 4 components only.

Here’s an example: user can select an image file from your local disk in Silverlight 3 only through an OpenFileDialog, while with the new drag/drop feature in Silverlight 4, she would be able drag a picture from the file system and drop it onto the application. Why not allow those with Silverlight 4 installed do it the easy way?

To make this work, the main application should be all Silverlight 3. We’d provide additional Silverlight 4 features in a separate XAP package, which would be downloaded later and tested for the right runtime version. In case user had the latest Silverlight runtime installed, we could bring in additional features in the application. For this post, I’m going to implement the abovementioned picture select feature by providing two controls:

  • a select button for choosing the picture through an OpenFileDialog (Silverlight 3 feature)
  • a drop canvas where user can drop the picture from the file system (Silverlight 4 feature)

Silverlight 3 control

Here’s how the BrowseForPictureControl would look like:

imageThis control would be contained in the main application. It exposes the PictureSelected event, with the FileInfo data passed as an event argument. Because the application is going to subscribe to this event for each control that exposes it, we need to make an interface for it and put that into a new project that would be shared among the both packages.

public interface IPictureControl
    event EventHandler<PictureSelectedEventArgs> PictureSelected;

public class PictureSelectedEventArgs : EventArgs
    public FileInfo File { get; set; }

    public PictureSelectedEventArgs(FileInfo file)
        File = file;

The control implements the this interface as:

private void OnBrowse(object sender, RoutedEventArgs e)
    OpenFileDialog dialog = new OpenFileDialog();
    bool result = dialog.ShowDialog() ?? false;
    if (result)

Silverlight 4 control

The improved Silverlight 4 control should be created in a new Silverlight 4 application project, that would be disconnected from the main project, but referencing the previously created shared project. The control looks simpler too:


And the interface implementation:

private void OnDrop(object sender, DragEventArgs e)
    IDataObject dataObject = e.Data as IDataObject;
    if (e.Data == null)
    FileInfo[] files = dataObject.GetData(DataFormats.FileDrop) as FileInfo[];


OK, controls done. Now, on to MEF.

Bringing in MEF

MEF for Silverlight 3 is available for download from Codeplex. You’ll need the following assemblies added as a reference in your main application:

  • System.ComponentModel.Composition
  • System.ComponentModel.Composition.Initialization.dll

The second assembly is only required to use from the main project, where composition is performed. The project that is shared between the SL3 and SL4 projects can reference just the first assembly from the list. Also, one downside of maintaining the compatibility with Silverlight 3 is that the Silverlight 4 project must reference the same System.ComponentModel.Composition assembly as other projects. No ‘native’ SL4 MEF there…

Attribute for version

Obviously, loading any Silverlight 4 based code into a Silverlight 3 application should be impossible, therefore we need to mark both of controls with information about the Silverlight runtime they require. Something in a way of:

[ExportablePictureSelector(RequiredVersion = "3.0")]
public partial class BrowseForPictureControl : UserControl, IPictureControl

for Silverlight 3 control, and:

[ExportablePictureSelector(RequiredVersion = "4.0")]
public partial class DragDropPictureControl : UserControl, IPictureControl

for Silverlight 4 control.

The ExportableSelector attribute is derived from MEF’s ExportAttribute and is declared as:

[AttributeUsage(AttributeTargets.Class, AllowMultiple = false)]
public class ExportablePictureSelectorAttribute : ExportAttribute, IPictureSelectorMetadata
    public ExportablePictureSelectorAttribute()
        : base(typeof(IPictureControl))

    public string RequiredVersion { get; set; }

Putting it all together

The main application provides a catalog of all the controls that were discovered:

[ImportMany(AllowRecomposition = true)]
public ObservableCollection<Lazy<IPictureControl, IPictureSelectorMetadata>> PictureControls { get; set; }

The PictureControls collection will change whenever a new export is discovered by MEF. When that happens, the newly discovered control will be added to the main form:

private void OnPictureControlsCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    foreach (Lazy<IPictureControl, IPictureSelectorMetadata> view in Views)
        Control c = view.Value as Control;
        if (!panel.Children.Contains(c) && Application.Current.Host.IsVersionSupported(view.Metadata.RequiredVersion))
            view.Value.PictureSelected += OnPictureSelected;

The above code shows that the main criteria for adding the control on the form is that it’s RequiredVersion is supported by the runtime – and that is checked with the interop IsVersionSupported method of the plugin host.

When picture is selected, the PictureSelected event is fired by the control and handled to display the picture:

private void OnPictureSelected(object sender, PictureSelectedEventArgs e)
    BitmapImage bi = new BitmapImage();
    image.Source = bi;

Of course, BrowseForPictureControl control being included in the main project, it will immediately be picked by MEF and inserted in the PictureControls collection. For Silverlight 4 based XAP package, however, we need to download it first. Here’s the InitializeContainer method, which initializes a new composition container and triggers the package download:

private void InitializeContainer()
    PackageCatalog catalog = new PackageCatalog();
    CompositionContainer container = new CompositionContainer(catalog);


    Package.DownloadPackageAsync(new Uri("CrossVersioning.Version4Enhancements.xap", UriKind.Relative), (e, p) =>
        if (p != null)


The Silverlight 4 package is asynchronously downloaded from the server and added to the package catalog. The last line is there to start the initial composition, causing the v3 control to immediately show up.


There… the application is set up. Users, having the Silverlight 3 runtime installed, will see the it as:image… and Silverlight 4 users will also see that additional feature:


This approach will let you gradually update your applications to use Silverlight 4, not forcing the users to update to the latest runtime immediately (although there would probably be no reason not to ;))

You can test the application right here:

Or download the source code from here. Enjoy.

Shidonni - Silverlight-based creative playground for your children

I stumbled upon this really nice Silverlight application today – Shidonni is a sort of social networking application for creative children – it lets them create their own animals, put them in a world that they’ve created, feed them with the food they’ve drawn and share them with their friends on the internet. A wide range of games is available, where children play with their own creations and compete with each other.

The application seems to be around for over a year now, but there was this extra which caught my attention. Since last November, Shidonni offers a service of making real plush toys from your child’s creations!


Shidonni appears to be one of the larger freely available Silverlight applications out there on the net, its features making it a good use case for Silverlight.

My MEF articles published on SilverlightShow

My two-part article on rebuilding an existing Silverlight application to use MEF (Managed Extensibility Framework) for “selective composition” is now live on (part 1, part 2). I took my Halloween Gallery application and made it pluggable so I can pull in different themes throughout the whole year (current themes include Halloween and Christmas).

Halloween Live Gallery Christmas gallery 

The original features are still there – geotagged photos are retrieved from Flickr API and the location where they were shot is shown on the Bing Map. If you’re interested in MEF, take a look at let me know what you think. The application will be released to Codeplex soon.

SilverlightShow Eco Contest is running a SilverlightShow Eco Contest! Write a Silverlight-based application that helps support and promote environment-friendly activities, and you can win great prizes, including a trip to MIX10 event in Las Vegas (MIX10 pass, 3-night hotel stay at Mandalay Bay Hotel and 1,000 USD for travel expenses included).

Read official rules here. But hurry, the contest ends on February 15th, 2010.

Display “My Pictures” in Silverlight application at design time

Following up on The ultimate hack for Silverlight in Blend post from Josh Smith, I tried to make Blend display pictures from the My Pictures folder right in my Silverlight application. Needless to say, it worked as advertised :)


The ViewModel is set through d:DataContext:

public class MainPageViewModel
    public MainPageViewModel()

    private void SetLocalPictures()
        string folder = Environment.GetFolderPath(Environment.SpecialFolder.MyPictures);
        IEnumerable<string> pictures = Directory.EnumerateFiles(folder);
        Pictures = (
            from p in pictures 
            select new Uri(string.Format("file://{0}", p.Replace('\\', '/')), UriKind.Absolute)

    public Uri[] Pictures { get; set; }

The thing is that this code wouldn’t work with Silverlight application running in a non-trust mode – it would throw a security exception. However, setting this ViewModel as the run-time DataContext and running with elevated permissions, the pictures would get displayed as well.

And of course this works in Visual Studio 2010 designer too:


A nice alternative for Blend’s sample data…