Setting User Control's DataContext from Code-Behind

This should be pretty easy, but it throws VS2008 for a serious loop.

I'm trying out WPF with MVVM, and am a total newbie at it although I've been developing for about 15 years, and have a comp. sci. degree. At the current client, I am required to use VB.Net.

I have renamed my own variables and removed some distractions in the code below, so please forgive me if it's not 100% syntactically perfect! You probably don't really need the code to understand the question, but I'm including it in case it helps.

I have a very simple MainView.xaml file:

<Window x:Class="MyApp.Views.MainView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Main Window" Height="400" Width="800" Name="MainWindow">

<Button Name="Button1">Show Grid</Button>
<StackPanel Name="teststack" Visibility="Hidden"/>

</Window>

I also have a UserControl called DataView that consists of a DataGrid:

<UserControl x:Class="MyApp.Views.DataView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:WpfToolkit="http://schemas.microsoft.com/wpf/2008/toolkit" >
<Grid>
    <WpfToolkit:DataGrid 
        ItemsSource="{Binding Path=Entries}" SelectionMode="Extended">
    </WpfToolkit:DataGrid>
</Grid>
</UserControl>

The constructor for the DataView usercontrol sets up the DataContext by binding it to a view model, as shown here:

Partial Public Class DataView

    Dim dataViewModel As ViewModels.DataViewModel

    Public Sub New()
        InitializeComponent()

        dataViewModel = New ViewModels.DataViewModel
        dataViewModel.LoadDataEntries()
        DataContext = dataViewModel
    End Sub

End Class

The view model for DataView looks like this (there isn't much in ViewModelBase):

Public Class DataViewModel
    Inherits ViewModelBase

Public Sub New()
End Sub

Private _entries As ObservableCollection(Of DataEntryViewModel) = New ObservableCollection(Of DataEntryViewModel)
Public ReadOnly Property Entries() As ObservableCollection(Of DataEntryViewModel)
    Get
        Return _entries
    End Get
End Property

Public Sub LoadDataEntries()

    Dim dataEntryList As List(Of DataEntry) = DataEntry.LoadDataEntries()
    For Each dataentry As Models.DataEntry In dataEntryList
        _entries.Add(New DataEntryViewModel(dataentry))
    Next

    End Sub
End Class

Now, this UserControl works just fine if I instantiate it in XAML. When I run the code, the grid shows up and populates it just fine.

However, the grid takes a long time to load its data, and I want to create this user control programmatically after the button click rather than declaratively instantiating the grid in XAML. I want to instantiate the user control, and insert it as a child of the StackPanel control:

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs) Handles Button1.Click

    Dim dataView As New DataView
    teststack.Children.Add(dataView)

End Sub

When I do this, as soon as the Button1_Click finishes, my application locks up, starts eating RAM, and hits the CPU about 50%.

Am I not instantiating my UserControl properly? It all seems to come down to the DataContext assignment in DataEntry's constructor. If I comment that out, the app works as expected (without anything in the grid, of course).

If I move this code block into Button1_Click (basically moving DataEntry's constructor code up a level), the app still fails:

dataViewModel = New ViewModels.DataViewModel
dataViewModel.LoadDataEntries()
dataView.DataContext = dataViewModel

I'm stumped. Can anybody give me some tips on what I could be doing wrong, or even how to debug what infinite loop my app is getting itself into?

Many thanks.

I eventually gave up on trying to get the DataContext on the UserControl set during instantiation of the UserControl (either in XAML or code). Now I load up the data and set the DataContext of the UserControl in an event in the UserControl (IsVisibleChanged, I believe). When I instantiate the UserControl in XAML, I have it's Visibility set to Hidden. When Button1 is clicked, I set the UserControl's Visibility to Visible. So the UserControl pops into view, and it loads up its data and DataContext is set. Seems to work, but also seems very kludgey. :-( Thanks for the help, folks!