I've been promising an example of the Model-View-ViewModel pattern for some time.  With the Feb CTP of WinFX out and the Feb CTP of Expression Interactive Designer close, I feel like I can post something that will work for awhile.  I had more ambitious plans for a complex, real-world example, but realized that 1)  I didn't have much time to write such a beast and 2)  It was hard to create a complex example that still clearly explained the principles. 

So, I came up with the idea of doing a toy contact database.  The core model classes looks like this:

public class Contact
{
      // Methods
      public Contact(string name, Gender gender, string favoriteColor);
      public override string ToString();

      // Properties
      public string FavoriteColor { get; }
      public Gender Gender { get; }
      public string Name { get; }
}

public class ContactDatabase
{
      // Events
      public event ContactsChangedEventHandler ContactDatabaseChanged;

      // Methods
      public ContactDatabase();
      public void AddContact(Contact newContact);
      private void OnContactDatabaseChanged(ContactsChangedType changeType, int index, Contact contact);
      public void RemoveContact(int index);

      // Properties
      public ReadOnlyCollection<Contact> Contacts { get; }
}

Notice the classes have no special WPF dependencies.  Imagine this is a pre-existing model, perhaps an interchange schema or a web-service with no UI or specific UI technology in mind.  What I will be demonstrating is how to wrap this Model in a ViewModel an then build a UI on that ViewModel, all without changing the Model and especially without mixing UI code into it.

But to start, I want to show how much you can do with WPF data binding to just bind directly to the model...without any additional code.  It turns out, quite alot.  Here's a scrap of XAML I created using Expression:

 <!-- The code will set the data context for this item -->
 <Grid  x:Name="MasterDetailContainer"
   Margin="28,25,28,11" RenderTransformOrigin="0.5,0.5">
  <Grid.ColumnDefinitions>
   <ColumnDefinition Width="0.45*"/>
   <ColumnDefinition Width="0.55*"/>
  </Grid.ColumnDefinitions>
  <Grid.RowDefinitions>
   <RowDefinition/>
  </Grid.RowDefinitions>
  
  <!-- The parent's data context is going to be of type ContactDatabase
       we bind the ListBox items to the ContactDatabase.Contacts property -->
  <ListBox x:Name="ContactsListBox"
    Margin="12,12,11,94" RenderTransformOrigin="0.5,0.5"
    ItemsSource="{Binding Path=Contacts}"
  
    IsSynchronizedWithCurrentItem="True"/>
    
  <ContentControl  x:Name="CurrentContactDetail"
    Margin="14,16,17,219" Grid.Column="1" RenderTransformOrigin="0.5,0.5"
    Content="{Binding Items.CurrentItem, ElementName=ContactsListBox, Mode=OneWay}"/>
    
    
  <Button x:Name="AddButton"
    HorizontalAlignment="Left" VerticalAlignment="Bottom" Margin="18,0,0,131"
    Width="86" Height="58" Grid.Column="1" RenderTransformOrigin="0.5,0.5"
    Content="Add"
    IsEnabled="false"/>
  <Button x:Name="RemoveButton"
    HorizontalAlignment="Stretch" VerticalAlignment="Bottom" Margin="135,0,93,131"
    Width="86" Height="58" Grid.Column="1" RenderTransformOrigin="1,0.48"
    Content="Remove"
    IsEnabled="false"/>
 </Grid>

The full project code at this point is attached.  Take a look at it.  In the next installment I will add a simple ViewModel.