TreeView.SelectedItemChanged Event (System.Windows.Controls)

Partial Public Class MainPage
    Inherits UserControl
    ' Create the topics collection. 
    Public Shared Topics As New ObservableCollection(Of Topic)()
    Public Sub New()
        InitializeComponent()

        ' Add some topics to the collection. 
        Topics.Add(New Topic("Using Controls and Dialog Boxes", Guid.NewGuid()))
        Topics.Add(New Topic("Getting Started with Controls", Guid.NewGuid()))
        Dim DataGridTopic As New Topic("DataGrid", Guid.NewGuid())
    DataGridTopic.ChildTopics.Add(New Topic( _
            "Default Keyboard and Mouse Behavior in the DataGrid Control", Guid.NewGuid()))
    DataGridTopic.ChildTopics.Add(New Topic( _
        "How to: Add a DataGrid Control to a Page", Guid.NewGuid()))
    DataGridTopic.ChildTopics.Add(New Topic( _
        "How to: Display and Configure Row Details in the DataGrid Control", _
         Guid.NewGuid()))
        Topics.Add(DataGridTopic)
        myTreeView.DataContext = Topics

End Sub

Private Sub myTreeView_SelectedItemChanged(ByVal sender As Object, _
    ByVal e As RoutedPropertyChangedEventArgs(Of Object)) _
    Handles myTreeView.SelectedItemChanged
    ' Set the data context of the text block to the selected value. 
    Dim myTreeView As TreeView = TryCast(sender, TreeView)
    idTextBlock.DataContext = myTreeView.SelectedValue
End Sub
End Class

' Simple business object. 
Public Class Topic
    Private titleValue As String
    Public Property Title() As String
        Get
            Return titleValue
        End Get
        Set(ByVal value As String)
            titleValue = value
        End Set
    End Property
    Private idValue As Guid
    Public Property Id() As Guid
        Get
            Return idValue
        End Get
        Set(ByVal value As Guid)
            idValue = value
        End Set
    End Property
    Private childTopicsValue As ObservableCollection(Of Topic)
    Public Property ChildTopics() As ObservableCollection(Of Topic)
        Get
            Return childTopicsValue
        End Get
        Set(ByVal value As ObservableCollection(Of Topic))
            childTopicsValue = value
        End Set
    End Property
    Private Sub New()
        ChildTopics = New ObservableCollection(Of Topic)()
    End Sub
    Public Sub New(ByVal title1 As String, ByVal id1 As Guid)
        Me.New()
        Title = title1
        Id = id1
    End Sub
End Class

public partial class MainPage : UserControl
{
    // Create the topics collection.
    static public ObservableCollection<Topic> Topics = 
        new ObservableCollection<Topic>();
    public MainPage()
    {
        InitializeComponent();

        // Add some topics to the collection.
        Topics.Add(new Topic("Using Controls and Dialog Boxes", Guid.NewGuid()));
        Topics.Add(new Topic("Getting Started with Controls", Guid.NewGuid()));
        Topic DataGridTopic = new Topic("DataGrid", Guid.NewGuid());
        DataGridTopic.ChildTopics.Add(
            new Topic("Default Keyboard and Mouse Behavior in the DataGrid Control", 
                Guid.NewGuid()));
        DataGridTopic.ChildTopics.Add(
            new Topic("How to: Add a DataGrid Control to a Page", 
                Guid.NewGuid()));
        DataGridTopic.ChildTopics.Add(
            new Topic("How to: Display and Configure Row Details in the DataGrid Control", 
                Guid.NewGuid()));
        Topics.Add(DataGridTopic);
        myTreeView.DataContext = Topics;

        //Associated a handler with the item changed event.
        myTreeView.SelectedItemChanged += 
            new RoutedPropertyChangedEventHandler<object>(myTreeView_SelectedItemChanged);
    }

    void myTreeView_SelectedItemChanged(object sender, 
        RoutedPropertyChangedEventArgs<object> e)
    {
        // Set the data context of the text block to the selected value.
        TreeView myTreeView = sender as TreeView;
        idTextBlock.DataContext = myTreeView.SelectedValue;
    }
}

// Simple business object.
public class Topic
{
    public string Title { get; set; }
    public Guid Id { get; set; }
    public ObservableCollection<Topic> ChildTopics { get; set; }
    private Topic()
    {
        ChildTopics = new ObservableCollection<Topic>();
    }
    public Topic(string title, Guid idValue) : this()
    {
        Title = title;
        Id = idValue;
    }
}

    <StackPanel x:Name="LayoutRoot" Background="White">
        <StackPanel.Resources>
            <sdk:HierarchicalDataTemplate x:Key="ChildTemplate" >
                <TextBlock FontStyle="Italic" Text="{Binding Path=Title}" />
            </sdk:HierarchicalDataTemplate>
            <sdk:HierarchicalDataTemplate x:Key="NameTemplate" 
                ItemsSource="{Binding Path=ChildTopics}" 
                ItemTemplate="{StaticResource ChildTemplate}">
                <TextBlock Text="{Binding Path=Title}" FontWeight="Bold" />
            </sdk:HierarchicalDataTemplate>
        </StackPanel.Resources>
        <sdk:TreeView Width="400"  Height="200" ItemsSource="{Binding}" 
            ItemTemplate="{StaticResource NameTemplate}" x:Name="myTreeView" 
	    SelectedValuePath="Id" />
        <StackPanel Orientation="Horizontal" >
            <TextBlock Margin="5" Text="Selected topic GUID:" />
            <TextBlock FontWeight="Bold" Margin="5" Text="{Binding}" x:Name="idTextBlock" />
        </StackPanel>
            </StackPanel>