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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:




Detecting duplicate instances of a running Silverlight application

This is a short tip for constraining your Silverlight applications to a single instance, something that’s quite popular in the desktop applications world. What you want to do is allow only the first instance of your application while rejecting all subsequent instances.

Silverlight 3 introduced a way for applications to communicate between each other, either on the same page or instantiated on a different browser instances (works even with Installed/OOB apps). The communication is performed by sender and receiver classes, which exchange messages through named channels. Each receiver must register a unique name for the channel or an exception will be thrown.

And that’s the trick. Listening on a specific named channel will act like a mutex. By catching the ListenFailed exception you get an option to display appropriate message or launch a different version of the application. All the work is done in App.Xaml.cs file:

private void Application_Startup(object sender, StartupEventArgs e)
{
    try
    {
        receiver = new LocalMessageReceiver("singleinstance");
        receiver.Listen();
        this.RootVisual = new MainPage();
    }
    catch (ListenFailedException)
    {
        this.RootVisual = new DuplicateInstancePage();
    }
}

The test project is available through here.



Halloween Live Gallery

With Halloween around the corner, it’s time for some scary photos… In this post I’ll explain how I built my demo application I showed at my Windows 7 Launch talk.

Expression Blend 3 shipped with a few interesting samples, available for immediate use. One of them is called Wall3D (Silverlight 3) and is a great example of one of the new Silverlight 3D features, called perspective transform.

image

This sample (perhaps a starter kit is a better description for it) features a 3D photo gallery, which sort of puts the viewer in the center of an oval “room”, full of photos, with an option to rotate the view to the left or right (flick / mouse click and pan), zoom in or out (mouse wheel), etc.. The kind of what people used to do in Flash; now it’s possible in Silverlight too. The sample serves also as a demonstration of yet another new Blend 3 feature, called Sample data – the photos on the above image were generated through this feature. Let’s explore the sample and see how we can push it further, shall we?

After opening Blend 3, switch to the Samples page and choose Wall3D (Silverlight 3) and the default project will be generated for you. image

You can test the application by hitting F5. You navigate through the gallery by flicking the view left or right and zoom in or out with your middle mouse button.

Examining the code that’s been created in the project will reveal the following:

  • the photos come from the sample data source (XML + photos, which are also included in the project – look into the SampleData folder)
  • “The wall” is driven by the CircularPanel3D control (a custom panel)

Knowing this, we’re ready to create our own 3D gallery. We’ll only need a single thing from this sample project, and that’s the CircularPanel3D.cs file, found in the root of the project. Copy and save that in some other folder for later reference, then start a new Silverlight 3 Application project in Blend.

I used an ItemsControl instead of ListBox to arrange and display the photos. Of course both will accept CircularPanel3D as their ItemsPanel, I just didn’t need item selection in this case. Here’s how it all looked in Blend designer:

Now what’s wrong with this picture? It’s hard to design something when you’ve got no visual feedback to help you with the layout and arrangements. I have already modified the ItemTemplate, but without the actual photos, it’s hard to do proper design work.  And that’s where the sample data comes in. To create a sample data source, open the Data panel and click on the second icon from the right image (Add sample data source). Choose Define New Sample Data, name the data source and click OK. You can shape the sample data source however you like – flat, hierarchical, with entities having simple or complex type properties, etc. For this gallery, I created the following source:

image

Bind this data source to the ItemsControl as its items source – voila!

Cool, much better. Modifying the ItemTemplate has just become a lot easier. Let’s add another element for displaying a bit more details about the photo (like the title and location where it was taken).

Photo view Details view

So we’ve got two views for the ItemTemplate, each view being represented with a separate element – one’s with the photo and the second one with details. We have to provide a way for user to switch between the two; how would we do this? Write code? Call the developer? Not necessarily. If we’re in luck, the appropriate piece of code may have already been written, waiting to be taken it used in Blend for declaratively specifying whatever we wanted to do to those elements and how. That piece of code is called a behavior. There are several places on the web to look for behaviors (as well as more info on what they are and how to produce them), but my first bets would be the Expression Gallery and Expression Blend Samples library on Codeplex; the letter containing some very handy behaviors.

I added a couple of behaviors to add interaction to gallery elements - FlipAction would switch the photo and details part through flip motion, triggered by DoubleClick trigger; and ScaleBehavior would enlarge the photo on mouse over. A couple of clicks for very cool-looking effect.

Let’s take a look at the data source... I decided to use Flickr to retrieve the photos, because it’s API is easy to use and can (amongst other things) return geo-location of the place where photo was taken (when available). This geo-location is then passed to the Bing Maps geocoding web serviceas an input parameter to retrieve the real-world address; these addresses can be seen on the bottom of the flipped photo.

image

Playing with geo-location was fun so I decided to take it a step further. I put together a special ShowMapAction, which is currently triggered by a mouse wheel over the photo (or details). The action simply shows the location on the interactive Bing Map (I used Bing Maps Silverlight Map Control for this).

image

Just a word of caution: Geo-encoded photos are cool, but be careful what you’re publishing on the net. The information may not always be used for good purposes.

The final result can be seen here (live). Right in time for keeping track with what’s going on on Halloween.

Finally I have to say I’m spending a lot more time in Blend since version 3 got out. It’s evolving into a great tool and behaviors are going to take a significant part in designer’s/integrator’s role in the future.

http://tozon.info/gallery/



Windows 7 Launch talk: Building cool applications with MS Expression tools

Windows 7 launch day was fun. I gave a talk on Expression tools (and related) – here’s the PowerPoint slide deck for those who asked for it:

I used Expression Blend 3 to build a photo viewer application, which I’ll blog about later; key points here were designer-developer workflow + using sample data and behaviors.

I blogged about the Microsoft ICE last year and I used that exact sample I’ve used in that blog post, but with one difference: did you know that by installing ICE on your desktop will, you can stitch panoramic (or large composite) photos right from your Windows Live Photo Gallery? It’s as easy as selecting the photos and click on the Extras menu item:

Create Image Composite...

Yet another option for stitching a bunch of photos together will give you the Deep Zoom Composer(free and not listed as an Expression tool, but sure looks and feels like it), which has similar features and much more compositing power (different zoom levels, layers, etc.)

And for closing I briefly showcased Expression Encoder 3 and IIS Smooth Streaming.

Yup, fun.



Slides and demo from Bleeding Edge’2009

On this year’s Bleeding Edge conference I had a talk on debugging with my fellow SQL Server MVP. While he covered some common pitfalls, awaiting developers on the SQL Server side, I focused on the Silverlight side of development and debugging:

  • possible issues with application deployment
  • options and strategies for returning WCF faults with Silverlight 3
  • using windbg with Silverlight application to track its execution
  • finding data binding failures and memory leaks

This was our sample application: Bleeding Edge Shoppe[opens in new window]

Bleeding Edge Shoppe

[The full source code will be available shortly.]

And the slide deck:



Silverlight LOB: Validation (#1)

When taking about data validation in applications, I usually describe the validation as the five-stage process or, put differently, five lines of defense against invalid data. In this post, I’ll write about the first line of defense – preventing the user entering the wrong data.

1. Preventing invalid input

This one’s logical, really. A user enters the data through input fields on some kind of input form, so naturally this would be the best place to put our first line of defense.

The first line of defense is about preventing user to enter invalid data into input fields. This doesn’t mean that if done proper and thorough, we wouldn’t need other places to check the data; it’s just the best place to filter out majority of faulty input that can happen during manual data entry. The goal here is to catch as many invalid data as possible, as soon as possible. This wouldn’t result only in better application responsiveness (no unnecessary trips to the server), the immediate feedback of invalid entry will provide a better user experience, possibly even educate the user to learn from her mistakes.

So, what are we talking about here?

A simple TextBox might not be the best solution for entering only numeric data. Seeing the TextBox on the input form, the user might expect she can enter anything she likes into the box, even if the label, put close by the input box, is saying to her: “Enter your age”. A kind of a NumericUpDown control visually gives user a much better idea of what should go into that box, plus she gets an option of manipulating that value; in this case, it’s adjusting the value with the Up and Down keys. In Windows Forms, for example, I liked to use a TextBox with a calculator dropdown for entering decimal data. Masked input boxes also work well, when you want the user to enter the data in a specific format.

If you don’t want to provide any visual clues that only numeric data should be entered in the input field and go for the standard TextBox, it’s very much recommended to handle the input for yourself and only allow numeric keys through. This is usually done by hooking into KeyDown event – either in codebehind class, or even better – with a custom TextBox behavior.

Yet another good example of filtering the data input to the underlying data type, is the DatePicker control. You can usually set the range of valid dates that can be selected and control whether or not date entry is required. With Silverlight DatePicker, it appears that date entry is always optional, even if bound to a non-nullable DateTime data type. Tabbing out of the DatePicker will leave the input box empty, but the bound property will still contain the old value. Hooking into DateValidationError or BindingValidationError event wouldn’t help so I tried to handle this case by manipulating the Selected date in the SelectedDateChanged event. Instead of doing it in the codebehind class, I created the following behavior:

public class RequiredDatePickerBehavior : Behavior<DatePicker>
{
    protected override void OnAttached()
    {
        base.OnAttached();
        AssociatedObject.SelectedDateChanged += OnSelectedDateChanged;
    }

    protected override void OnDetaching()
    {
        base.OnDetaching();
        AssociatedObject.SelectedDateChanged -= OnSelectedDateChanged;
    }

    private void OnSelectedDateChanged(object sender, SelectionChangedEventArgs e)
    {
        if (e.AddedItems.Count == 0 && e.RemovedItems.Count > 0)
        {
            AssociatedObject.SelectedDate = (DateTime)e.RemovedItems[0];
        }
    }
}

… which can be used as:

<controls:DatePicker SelectedDate="{Binding BirthDate, Mode=TwoWay}"
                     Grid.Row="1" Grid.Column="1">
    <i:Interaction.Behaviors>
        <local:RequiredDatePickerBehavior />
    </i:Interaction.Behaviors>
</controls:DatePicker>

Attaching this behavior to the DatePicker will revert the date to the last valid value in case of deleting the text from the input box and thus making the DatePicker non-nullable.

Behaviors in general are a great way to extend an existing type (or types) of control and can be used for a variety of things. In this post I’ve shown a way to enhance the Silverlight DatePicker control to prevent entering empty values in cases when date is required. Remember next time you’ll find yourself coding KeyDown or similar control event handler in page’s codebehind class: consider writing a behavior!

To be continued…

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