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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)
    {
        OnPictureSelected(dialog.File);
    }
}

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:

image

And the interface implementation:

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

    OnPictureSelected(files[0]);
}

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:

[MetadataAttribute]
[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))
        {
            panel.Children.Add(c);
            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();
    bi.SetSource(e.File.OpenRead());
    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();
    catalog.AddPackage(Package.Current);
    CompositionContainer container = new CompositionContainer(catalog);
    container.ComposeExportedValue(catalog);

    CompositionHost.InitializeContainer(container);

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

    PartInitializer.SatisfyImports(this);
}

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.

Conclusion

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:

image

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!

image

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 SilverlightShow.net (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

SilverlightShow.net 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 :)

Blend

The ViewModel is set through d:DataContext:

public class MainPageViewModel
{
    public MainPageViewModel()
    {
        SetLocalPictures();
    }

    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)
            ).ToArray();
    }

    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:

VS2010

A nice alternative for Blend’s sample data…



My articles on SilverlightShow

A few of my Silverlight articles were published on the SilverlightShow site this past two months. The first one is an introduction to Silverlight/(WPF)/Blend behaviors, where I create a Silverlight Halloween Sound Player without writing a single line of code – the application is composed entirely in Expression Blend, using various behaviors.

Halloween Sound Player

I also used behaviors for another article, to showcase some of the new Silverlight 4 features: WebCam capture support, printing, drag/drop, clipboard, commanding, some databinding enhancements and implicit styling support. The result is a nice doodling application, which can be used to entertain your kids.Camdoodle

The third article was about creating a Europe Weather Map with Silverlight, showing current weather conditions for some of the larger cities in Europe. It was mostly about using the Bing Maps Silverlight Control SDK, but fun anyway.

Europe Weather map

You can expect more articles appearing on SilverlightShow in the next days/months. Leave a comment if you find them useful.



Silverlight 4 WebCam zoom

Fooling around with Silverlight’s WebCam support. The application below will let you zoom in and out of WebCam capture and pan around. Nothing special, just a quick POC for the project I’m building. Silverlight 4 required.



Developers, please mind the locale!

I’m observing this really irritating trend with new software lately…

I followed up on a couple of tweets today to try the new Silverlight application everyone was RT’ing of. Clicked on the link and the loading animation began. Seconds later, it… stopped.

Huh?

Then I noticed an icon in IE’s left bottom corner…

image

The following detailed message confirmed my assumptions about what caused the error:

image

“Input string was not in a correct format”!

I’m sure that if you live outside US/UK and follow Silverlight community, you have encountered this error before. For example, I’ve been to at least two online events in the past year, with live streaming content delivered over a Silverlight player, which displayed this very same error when launched.

Here is the list of some other apps that I’ve worked with recently, that have been showing the same symptoms. To name just a few:

Silverlight Bing Maps, specifically the Twitter app – can you find the difference between these two links?

http://www.bing.com/maps/explore/#5872/style=auto&lat=46.037671&lon=14.533958&z=11&
pid=5874/5003/0.40326=s&o=&a=0&n=0

and

http://www.bing.com/maps/explore/#5872/style=auto&lat=46,037671&lon=14,533958&z=11&
pid=5874/5003/0.40326=s&o=&a=0&n=0

The first link uses a dot as a decimal separator and will work for English locales, while the second one uses commas and will work for non-English locales (speaking generally). Note that URL will be converted to the default format when application is loaded, probably throwing you somewhere in an ocean, if the numbers weren’t in the expected format.

Live Labs Pivot (desktop app) will crash on startup when locale is not set to English.

Six-Degrees Search is the application I’ve tried to run today. A Silverlight app, based on the EntityCube entity search engine and being developed by Microsoft Research. Regional settings need to be set to English locale for application to load correctly.

Mentioned software might be labeled Beta or prototype, but that hardly justifies the fact that developers didn’t support non-English locales from the very start. Therefore I’m taking this blog post to appeal to all Silverlight developers, especially those working with regional settings set to English natively:

Please, make your applications respect local regional settings as early in the development as possible. Silverlight may be cross-platform and cross-browser, but developers, not taking local regional settings into the account, don’t even make it cross-locale.

Just in case anyone encounters a weird behaving application, showing symptoms described at the very top of this post, this is one of the things to try first: The most likely cause for the above error is a wrong date or number format. Changing your local regional settings will probably help:

image



MVVM with WPF, Silverlight, and… Windows Forms

In my post-NTK09 conference blog post I mentioned one of my MVVM demos was about sharing a ViewModel between WPF, Silverlight and even Windows Forms application. I got a lot of requests for posting sample code online since then, which I intended to do earlier, but because the sample application code was closely related to the conference, I wanted to create a whole new sample application first and share that. Of course time passed and other things kept me busy from actually doing it. With Silverlight 4 Beta coming out recently, things progressed even further in so I decided to keep things as they were, and post the original sample code. I’ll explain it in few lines (and pictures) here, and the source code can be found here.

What’s it all about?

The purpose of the sample (and my NTK09 talk in general) was about the MVVM pattern principle and how it can be used to totally separate the User Interface from the business logic and data. The application I built was a conference session schedule viewer / editor. Technically, there are three application flavors: WPF, Silverlight and WinForms. They share the same data access (WCF service) and ViewModel. The only thing different between the three is their UI implementation.

imageimageimage

Notice the small arrow overlay over the C# icon on Silverlight and WinForms PageViewModel.cs? That’s because both project are linking the original file from the WPF project, which I created first. That means that ViewModel is exactly the same across all three projects when they are compiled. And with all three project, this is the ViewModel that serves up the main page.

The WPF project

I created the WPF project to ‘just work’. I didn’t bother with styling and the looks, I intentionally left it ugly. I used Prism for commanding and WCF based web service for communicating the data.

image

The ‘Dan’ (Day) and ‘Kategorija’ (Category) serve as the filter for the session list on the left. Each combo box change results in a server request which returns new data for filling the session list. Other fields are editable session details fields. Three buttons on the top left correspond to New, Edit and Delete, in that order.

The Silverlight project

The Silverlight project differ from WPF in that that it’s in color :)

Silverlight

Prism is still used for commanding, but the UI is quite different. I even provided the View (above) and Edit (bottom) screens.

Silverlight Edit

As said, the difference between the WPF and Silverlight applications is just and only different XAML. And both have zero code-behind code. Moving on to…

The Windows Forms project

I  didn’t bother much with making Windows Forms project to work. I last coded anything in WinForms 2+ years ago so I suspect I won’t have to go there again… However, this is the UI I put together:

Windows Forms

It’s very similar to WPF, but data bindings perform much slower. Data bindings? There’s data bindings in WinForms too?

LOL. Sometimes I really do get questions like that. Anyway, let’s see the ‘code behind’. [There’s actually quite a few lines of code behind in Windows Forms because it’s used to instantiate and initialize all controls on the screen. That code is stored in the .designer file and I’m ignoring it as the code behind]

private void MainForm_Load(object sender, EventArgs e)
{
    PageViewModel viewModel = new PageViewModel();

    dayBox.DataBindings.Add("DataSource", viewModel, "Days");
    categoryBox.DataBindings.Add("DataSource", viewModel, "Categories");
    categoryBox.DisplayMember = "Name";
    speakerBox.DataBindings.Add("DataSource", viewModel, "Speakers");
    speakerBox.DisplayMember = "FullName";
    speakerBox.ValueMember = "Id";
    startTimeBox.DataBindings.Add("DataSource", viewModel, "TimeValues");
    endTimeBox.DataBindings.Add("DataSource", viewModel, "TimeValues");
    sessionList.DataBindings.Add("DataSource", viewModel, "Sessions");
    sessionList.DisplayMember = "Title";

    dayBox.DataBindings.Add("SelectedValue", 
        viewModel, "SelectedDay", true, DataSourceUpdateMode.OnPropertyChanged);
    categoryBox.DataBindings.Add("SelectedValue", 
        viewModel, "SelectedCategory", true, DataSourceUpdateMode.OnPropertyChanged);
    sessionList.DataBindings.Add("SelectedValue", 
        viewModel, "SelectedSession", true, DataSourceUpdateMode.OnPropertyChanged);
    speakerBox.DataBindings.Add("SelectedValue", 
        viewModel, "SelectedSession.SpeakerId", true, DataSourceUpdateMode.OnPropertyChanged);

    startTimeBox.DataBindings.Add("Text", 
        viewModel, "SelectedSession.StartTime", true, DataSourceUpdateMode.OnValidation);
    endTimeBox.DataBindings.Add("Text", 
        viewModel, "SelectedSession.EndTime", true, DataSourceUpdateMode.OnValidation);
    titleBox.DataBindings.Add("Text", 
        viewModel, "SelectedSession.Title", true, DataSourceUpdateMode.OnValidation);
    descriptionBox.DataBindings.Add("Text", 
        viewModel, "SelectedSession.Description", true, DataSourceUpdateMode.OnValidation);

    newButton.Click += (s, ev) => 
        { viewModel.NewSessionCommand.Execute(null); };
    editButton.Click += (s, ev) => 
        { viewModel.EditSessionCommand.Execute(viewModel.SelectedSession); };
    deleteButton.Click += (s, ev) => 
        { viewModel.DeleteSessionCommand.Execute(viewModel.SelectedSession); };
    saveButton.Click += (s, ev) => 
        { viewModel.EndEditSessionCommand.Execute(viewModel.SelectedSession); };
    cancelButton.Click += (s, ev) => 
        { viewModel.CancelEditSessionCommand.Execute(viewModel.SelectedSession); };
}

This is all the code for the main form. You’ll notice it’s all used for binding controls to various properties on the ViewModel. I could also get rid of some of the lines by setting the properties on the WinForms designer (thus moving them to the .designer file). The last section wires button clicks to execute commands in the ViewModel.

There is absolutely no business logic in this code which makes it very similar to declarative XAML in WPF and Silverlight projects. I was toying with the idea of making an Extender Provider to get rid of the above lines completely and do it all just with the Windows Forms designer – I made a working prototype, but wasn’t generic enough to include it in the sample.

Source code

Bellow is the full source for all three main and related projects. Also included is the Test project with a few Silverlight Unit Test Framework tests. Database is not included so you’ll not be able to actually run any of the applications. Sorry. I’ll post the Silverlight version online when time permits.



Silverlight LOB: Validation (#2 – Annotations and shared classes)

In my previous post, I wrote about “the first line of defense” against inputting invalid data in Silverlight applications (or any kind of application, for that matter) – preventing the user from entering invalid data through some an input form. Input form fields are commonly directly bound to the underlying object’s properties – either directly or through a of value converter – in both cases the entered value gets assigned to the bound object’s property; and this is exactly the place where we would want to put our second line of defense.

Silverlight 3 supports data validation. The majority of controls now feature new visual states for presenting themselves whenever they are associated with invalid data. Putting a control into the invalid state is as easy as throwing an exception in its bound property’s setter code:

public DateTime BirthDate
{
    get { return birthDate; }
    set
    {
        if (birthDate == value)
        {
            return;
        }

        if (birthDate > DateTime.Today)
        {
            throw new ArgumentException("The birth date is invalid.");
        }

        birthDate = value;
        OnPropertyChanged("BirthDate");
    }
}

When the property is set to an invalid date, the exception gets thrown. This exception is then caught by the data binding engine, which in turn triggers the BindingValidationError event, prompting the control to go to invalid state:

 image

This kind of notification can be enabled by setting binding’s ValidatesOnExceptions and NotifyOnValidationError properties to true.

System.ComponentModel.DataAnnotation

There is another way to perform validation over entity’s properties:  by using validators from the System.ComponentModel.DataAnnotation assembly. What you do is put an appropriate attribute above the property definition, describing the kind of validation to performed over property value.

[Required(ErrorMessage = "The date of birth is required.")]
public DateTime BirthDate
{
    get { return birthDate; }
    set
    {
        if (birthDate == value)
        {
            return;
        }

        birthDate = value;
        OnPropertyChanged("BirthDate");
    }
}

You can even write your own validation attributes by deriving from the ValidationAttribute class and overriding the validation method. Here’s an example to match my first method of validation (throwing an exception in property setter):

public class BirthDateValidationAttribute : ValidationAttribute
{
    protected override ValidationResult IsValid(object value, 
ValidationContext validationContext) { if (value == null) { return ValidationResult.Success; } DateTime date = (DateTime)value; if (date > DateTime.Today) { return new ValidationResult("The birth date is invalid."); } return ValidationResult.Success; } }

Let’s put this to work. Say we’re using shared entity classes in our project; a kind of a real world scenario. When projects are set up as described in my previous blog entry, we immediately bump into a problem – decorating the Person’s BirthDate property with the new BirthDateValidationAttribute results with the compilation error: it’s just that full .NET framework’s ValidationAttribute implementation differs form how Silverlight’s version is implemented and therefore above BirthDateValidationAttribute can’t be shared between both entity projects:

Client side: protected abstract ValidationResult IsValid(object value, ValidationContext validationContext)
Server side: public abstract bool IsValid(object value)

To work around this, we need to create a dummy validator attribute class in the server side entity project, having the same name as its client counterpart, except always returning true as the validation result:

public class BirthDateValidationAttribute : ValidationAttribute
{
    public override bool IsValid(object value)
    {
        return true;
    }
}

Validation

Instead of throwing an exception from the property trigger as in the previous example, we can now simply call the validation method, which would validate against every ValidationAttribute defined for the property.

Modified Property definition (Validate() method is called instead of throwing an exception):

[DataMember]
[BirthDateValidation]
public DateTime BirthDate
{
    get { return birthDate; }
    set
    {
        if (birthDate == value)
        {
            return;
        }

        Validate("BirthDate", value);
        birthDate = value;
        OnPropertyChanged("BirthDate");
    }
}

Because we only want to validate properties on the client, we need to implement the Validate() method just on the client side. But since the Person class is shared, we really have to include this method on both sides, except we would implement it differently.

In the end, Validate() method on the client is defined as:

private void Validate(string propertyName, object value)
{
    Validator.ValidateProperty(value, new ValidationContext(this, null, null)
    {
        MemberName = propertyName,
    });
}

… while the server side method can be left empty:

private void Validate(string propertyName, object value)
{
}

Single base class for entities?

To avoid having duplicate validation methods for all entities, it’s best to put it in a single base page, where you would put all the common entity code (like INotifyPropertyChanged etc.). In this case, partial methods are going to prove themselves very useful:

Main base class part:

partial void ValidateProperty(string propertyName, object value);
protected void Validate(string propertyName, object value)
{
    ValidateProperty(propertyName, value);
}

Client side base class part:

public partial class EntityBase
{
    partial void ValidateProperty(string propertyName, object value)
    {
        Validator.ValidateProperty(value, new ValidationContext(this, null, null)
        {
            MemberName = propertyName,
        });
    }
}

We can just leave the server side base class part out and forget about it. The best thing with with partial methods is that you don’t have to provide any implementation if you don’t want to – in which case the method simply won’t be called.

Source code for this project is available: