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[Required(ErrorMessage = "Field 'FirstName' is required.")]
public string FirstName
{
    get
    {
        return this.firstName;
    }
    set
    {
        this.firstName = value;
        this.OnPropertyChanged("FirstName");
    }
}

Of course the article comes with a nice demo application:

You can read the full article here: Attributes-based validation in a WPF MVVM application

Here is a list of the changes in this new version:

• application updated to Silverlight 4
• support is now detailed for WPF, Silverlight and Windows Phone
• new frameworks added (MEFedMVVM…)
• framework’s logo added
• download count added (based on the information I found on CodePlex website)
• about window

As always, feel free to give feedback

Actually and as you already know if you can write XAML like Text={Binding …} it is only because Text is a Dependency Property. Also, dependency properties are defined in a static way (so that if you have 50 textboxes you don’t have to instantiate 50 times the Text property). The default behavior for the mode of the binding (TwoWay, OneWay, etc.) can be found in the static declaration of the dependency property. For example, in the case of the Text property of the TextBox we have:

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TextProperty = DependencyProperty.Register(
	"Text", 
	typeof(string), 
	typeof(TextBox), 
	new FrameworkPropertyMetadata(
		string.Empty, 
		FrameworkPropertyMetadataOptions.Journal 
		| FrameworkPropertyMetadataOptions.BindsTwoWayByDefault,
	new PropertyChangedCallback(TextBox.OnTextPropertyChanged), 
	new CoerceValueCallback(TextBox.CoerceText),
	true, 
	UpdateSourceTrigger.LostFocus));

The interesting part here if of course the BindsTwoWayByDefault option. Note that this is the only default option available (we can’t have a OneWayToSource binding by default).

I guess many Windows Phone 7 developers have been waiting for this news since many weeks. It’s finally official: the Beta build of the Windows Phone 7 tools is out. If you want to download the new version here is the link.

This new version has been released during WPC (Microsoft Worldwide Partner Conference). For more information, please check-out:

• the post on the Windows Phone Developer Tools blog.
• this post by Jaime Rodriguez about all breaking change between the April CTP Refresh and the Beta build
• this post by the Blend team about the new features available in Blend
• the release note

Here are a summary of the changes in this new version:

• Despite HW acceleration effects have been removed from the platform (DropShadow and Blur effects are now no-op). This feature might come back later.
• Compatibility with Blend 4 RTM
• API near final
• Various fixes

Note that panorama and pivot controls are coming in the next weeks… Grab you copy now and enjoy Windows Phone 7 development

This is the very first year I got the MVP award. I’m very proud to have this recognition from Microsoft and it is giving me new ideas for the future. I started this blog almost 2 years ago now and I’d never imagine I’d get so much feedback about it. My MVP award is also recognizing my work in the French community (on the developpez.com website) or for conferences I’m giving in my daily job.

The MVP award will be also for me the occasion to have pre-release of Microsoft software (but I’ll not be able to publicly give information about them since I’ve just signed an NDA) and also to enjoy a free MSDN-Premium subscription !

For more information about the MVP Award Program you can check-out:

• the home page of the program
• the blog the program

Thanks to all my readers also who are giving me feedback and support.  I’d also like to thank my co-workers who are helpful in my daily job. I’m very lucky to be part of this very nice team. By reading posts before they go public (Charlotte, Fred !) or discussion about software programming in general (the whole Pythagore group!) I get cool ideas about things I want to share. So thank you every one for supporting me

A similar event has just been launched for Windows Phone 7 development at challenge-windowsphone7.developpez.com

(tr: “Let’s go !” “World cup ?” “No… Windows Phone 7 challenge by developpez.com !”)

The challenge is made of 6 steps:

1. Tools : download and install the required tools
2. Quizz : first basic quizz
3. Silverlight development
4. Silverlight and push notifications
5. XNA
6. Quizz : advanced quizz

Each winner will have the following gifts:

This kind of challenge is really helpful to discover a new technology the funny way ! I hope I’ll get my “I Love Windows Phone” tee-shirt to wear it this summer

Windows Phone 7 SDK comes with a set of Task (in the Microsoft.Phone.Tasks namespace). A task can be launched from your application in order to perform some work. Currently available tasks are:

• Capture Camera (StartCameraTask)
• Choose Email Address (EmailAddressChooserTask)
• Compose Email (EmailComposeTask)
• Open Market Place (MarketplaceLauncher)
• Open Media Player (MediaPlayerLauncher)
• Make Phone Call (PhoneCallTask)
• Pick Phone Number (PhoneNumberChooserTask)
• Choose Photo (PhotoChooserTask)
• Save Email (SaveEmailAddressTask)
• Save Phone Number (SavePhoneNumberTask)
• Search (SearchTask)
• Compose SMS (SmsComposeTask)
• Browse Web (WebBrowserTask)

In order to launch a task from your application, all you need to do is to instantiate the associated type and call the Show() method.

Here is a sample code which launchs the StartCameraTask and then gets the capture images in order to use it in a standard Silverlight Image control:

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// launch the camera capture when the user touch the screen
this.MouseLeftButtonUp += (s, e) => new CameraCaptureTask().Show();
 
// this static event is raised when a task completes its job
ChooserListener.ChooserCompleted += (s, e) =>
{
    var taskEventArgs = (TaskEventArgs<PhotoResult>)e;
    var photoStream = taskEventArgs.Result.ChosenPhoto;
 
    var bitmapImage = new BitmapImage();
    bitmapImage.SetSource(photoStream);
 
    this.image.Source = bitmapImage;
};

The image is just a standard Silverlight Image control:

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<Image x:Name="image"/>

The emulator while the task is running:

The captured image (shown once the task has completed):

If you haven’t download the tool already, go ahead and grab them ! Everything is available for free in a single download at http://developer.windowsphone.com/windows-phone-7-series/.

Hope this helps

Note: even though the StartCameraTask is now working, this is not yet the case for all the tasks…

Note: this problem did not occur if you’re using the first CTP of the WP7 tools

To reproduce the bug:

• Create a new Windows Phone 7 application in VS2010
• Add a new page (use the default name: Page1)
• In the MainPage, add the following XAML code:

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<ListBox>
  <Button MouseLeftButtonDown="Handler"/>
</ListBox>

• In the code-behind, add the following handler:

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private void Handler(object sender, MouseButtonEventArgs mouseButtonEventArgs)
{
    this.NavigationService.Navigate(new Uri("/Page1.xaml", UriKind.Relative));
}

• Run the application and click on the TextBlock
• You’ll get an ArgumentException with the following StackTrace:

at MS.Internal.XcpImports.MethodEx(IntPtr ptr, String name, CValue[] cvData)
at MS.Internal.XcpImports.MethodPack(IntPtr objectPtr, String methodName, Object[] rawData)
at MS.Internal.XcpImports.UIElement_TransformToVisual(UIElement element, UIElement visual)
at System.Windows.UIElement.TransformToVisual(UIElement visual)
at System.Windows.Controls.ScrollViewer.OnManipulationStarted(ManipulationStartedEventArgs e)
at System.Windows.Controls.Control.OnManipulationStarted(Control ctrl, EventArgs e)
at MS.Internal.JoltHelper.FireEvent(IntPtr unmanagedObj, IntPtr unmanagedObjArgs, Int32 argsTypeIndex, String eventName)

Analysis:

It took me some time to reproduce this problem in a very simple application. At the very beginning, I though it has something do to with the EventToCommand behavior I was using (from the famous MVVM-Light framework of Laurent Bugnion) but after talking with Laurent it was clear it wasn’t the case.

The StackTrace seems to indicate a problem with the ScrollViewer of the ListBox…

Workaround:

Several possibilities seems to be working:

1. Change the ListBox to an ItemsControl
2. Or, change the event to ManipulationCompleted

I didn’t find the correct location in order to log this issue on Microsoft Connect. Pleas let me know if you have the URL

Then the resource is automatically created for you:

Note that it works with converter too:

R# 5.0 has been released a couple of weeks ago. Go ahead and grab your copy !

Without any doubt MVVM is now the most used framework to leverage WPF and Silverlight functionalities in the best way ! During the last Mix, 3 sessions were dedicated to this methodology (you can watch the videos online here).

As you already know one of the key advantage of the MVVM methodology is to improve the testability of the overall application by reducing the amount of code in the code-behind and producing ViewModel classes which are testable. We use to say that ViewModel classes are testable because:

• they are not coupled to UI concepts (controls, focus, keyboard input…)
• they can wrap model objects using interfaces (for instance a PersonViewModel wraps a IPerson object)
• they are not subclassing a UI control (such as Button or Window)

Today I’d like to share a technique I’m using to facilitate the unit tests of some properties of my ViewModel classes.

Let’s use a very simple ViewModel class as example:

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public class PersonViewModel : ViewModelBase
{
  private IPerson person;
  private bool isSelected;
 
  public string Name 
  {
     get
     {
        return this.person.Name;
     }
     set
     {
        this.person.Name = value;
        this.OnPropertyChanged("Name");
     }
  }
 
  public bool IsSelected
  {
    get
    {
      return this.isSelected;
    }
    set
    {
      this.isSelected = value;
      this.OnPropertyChanged("IsSelected");
    }
  }
 
  // rest of the code omitted for simplicity
}

The Name property, as usually with the MVVM pattern gets its value from the wrapped model object. The easiest way to unit test this property is to use a mocking library. Here is a example using MOQ (my favourite mocking library):

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[Test]
public void TestName()
{
  var mockPerson = new Mock<IPerson>();
 
  var vm = new PersonViewModel(mockPerson.Object);
 
  vm.Name = "Jeremy";
 
  // verify that the Name property of the IPerson interface has been set
  mockPerson.VerifySet(p => p.Name = "Jeremy");
}

The Selected property is different because it doesn’t wrap a model property. It’s an information that is added to the ViewModel layer in order to control a UI-related property (for example the IsSelected property of a ListBoxItem). This technique is heavily used to have ViewModel classes interact with the WPF or Silverlight TreeView or ListBox control (you can check out this excellent article of Josh Smith for more detail).

In order to unit test this property, we must:
1/ ensure the PropertyChanged event of the INotifyPropertyChanged is raised properly
2/ ensure we can write a value and read back the correct value

Here is a sample code which does this unit test:

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[Test]
public void TestName()
{
var vm = new  PersonViewModel();
bool propertyChanged = false;
 
vm.PropertyChanged += (s, e) => propertyChanged = e.PropertyName ==  "Name";
vm.Name = "newName";
 
Assert.IsTrue(propertyChanged);
Assert.AreEqual("newName", vm.Name);
}

It quickly become cumbersome to copy/paste this unit test for all the ViewModel properties we have. That’s the reason I started thinking about another way to do it…

Here is the feature I’m proposing:

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[Test]
public void TestName()
{
var vm = new PersonViewModel();
TestHelper.TestProperty(vm, v => v.IsSelected);
}

In this sample, I’m telling I want to test the IsSelected property of the PersonViewModel type. The advantages are:
1/ less code involved : 1 line to test 1 property
2/ intellisense support in order to prevent typing error and no more “magic” string to give the name of the property
3/ refactoring the name of the property will refactor this sample code too
4/ automatic generation of default test values behind the scene

How does it works ?

• TestProperty treats the second parameter as an Expression<Func> and not as a Func directly
• Using expression tree (the “v => v.IsSelected” part),  I’m able to retrieve the name of the property and its type
• Using reflection, I’m able to get and set the value
• Depending on the type of the property (string, bool, int, double), I have default values write and read back (with a test to ensure that the PropertyChanged event has been raised properly).

Here is the code of the TestPropertyMethod:

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public static void TestProperty<T, U>(T viewmodel, Expression<Func<T, U>> expression)
    where T : INotifyPropertyChanged
{
    if(expression.Body is MemberExpression)
    {
        MemberExpression memberExpression = (MemberExpression) expression.Body;
 
        if (expression.Body.Type == typeof(bool))
        {
            TestViewModelProperty(viewmodel, memberExpression.Member.Name, true, false);
        }
        else if (expression.Body.Type == typeof(string))
        {
            TestViewModelProperty(viewmodel, memberExpression.Member.Name, "value1", "value2");
        } 
        else if (expression.Body.Type == typeof(int))
        {
            TestViewModelProperty(viewmodel, memberExpression.Member.Name, 1, 99);
        }
        else if (expression.Body.Type == typeof(double))
        {
            TestViewModelProperty(viewmodel, memberExpression.Member.Name, 1.0, 99.0);
        }
        else
        {
            throw new NotSupportedException("Type is not supported");
        }
   }
}

And the TestViewModelProperty:

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private static void TestViewModelProperty<T, U>(T viewModel, string propertyName, U value1, U value2)
    where T : INotifyPropertyChanged
{
    bool propertyChanged;
    viewModel.PropertyChanged += (s, e) => propertyChanged = e.PropertyName == propertyName;
 
    propertyChanged = false;
    viewModel.SetValue(propertyName, value1);
    Assert.IsTrue(propertyChanged);
    Assert.IsTrue(viewModel.GetValue<U>(propertyName).Equals(value1));
 
    propertyChanged = false;
    viewModel.SetValue(propertyName, value2);
    Assert.IsTrue(propertyChanged);
    Assert.IsTrue(viewModel.GetValue<U>(propertyName).Equals(value2));
}

I’m using 2 extensions methods in order to get and set value from the ViewModel object using reflection. Here they are:

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private static T GetValue<T>(this object obj, string propertyName)
{
    var propertyInfo = obj.GetType().GetProperty(propertyName);
    return (T)propertyInfo.GetValue(obj, null);
}
 
private static void SetValue<T>(this object obj, string propertyName, T value)
{
    var propertyInfo = obj.GetType().GetProperty(propertyName);
    propertyInfo.SetValue(obj, value, null);
}

Please feel free to download the source code of the ViewModelTestHelper class.