ListBox ItemTemplateSelector doesn't work - wpf

Question

I am attempting to use an ItemTemplateSelector on a WPF ListBox and have looked at several examples online. Seemed simple enough but I cannot get it to work. I am hoping that someone can tell me where I've gone wrong:
Fist, I have an DataTemplateSelector class defined as follows:
Public Class DocketDataTemplateSelector
Inherits DataTemplateSelector
Public Overrides Function SelectTemplate(ByVal item As Object, ByVal container As DependencyObject) As DataTemplate
Return DataDocketHeaderTemplate
End Function
Private _DataDocketHeaderTemplate As DataTemplate
Public Property DataDocketHeaderTemplate() As DataTemplate
Get
Return _DataDocketHeaderTemplate
End Get
Set(ByVal value As DataTemplate)
_DataDocketHeaderTemplate = value
End Set
End Property
Private _DataDocketDataTemplate As DataTemplate
Public Property DataDocketDataTemplate() As DataTemplate
Get
Return _DataDocketDataTemplate
End Get
Set(ByVal value As DataTemplate)
_DataDocketDataTemplate = value
End Set
End Property
End Class
Very simple - just returns the DataDocketHeaderTemplate datatemplate for the time being until I can get it to work.
I then have my user control with the following as its resource definition:
<UserControl.Resources>
<DataTemplate x:Key="docketHeaderTemplate">
<TextBlock Text="Header Row Test" Background="Yellow"/>
</DataTemplate>
<DataTemplate x:Key="docketDataTemplate">
<TextBlock Text="Data Row Test" Background="Green"/>
</DataTemplate>
<local:DocketDataTemplateSelector DataDocketHeaderTemplate="{StaticResource docketHeaderTemplate}" DataDocketDataTemplate="{StaticResource docketDataTemplate}" x:Key="myDataTemplateSelector"/>
</UserControl.Resources>
The ListBox in the user control is simply defined like this:
<ListBox ItemsSource="{Binding TestData}" ItemTemplateSelector="{StaticResource myDataTemplateSelector}"/>
Then finally, my TestData list is defined in my bound viewmodel like so:
Private _listTestData As ObservableCollection(Of String) = Nothing
Public Property TestData As ObservableCollection(Of String)
Get
If _listTestData Is Nothing Then
_listTestData = New ObservableCollection(Of String)
_listTestData.Add("Row 1")
_listTestData.Add("Row 2")
_listTestData.Add("Row 3")
End If
Return _listTestData
End Get
Set(ByVal value As ObservableCollection(Of String))
_listTestData = value
NotifyPropertyChanged("TestData")
End Set
End Property
Now, I expect I would see a list of 3 rows in my listbox all saying 'Header Row Test' (since my datatemplateselector is always returning DataDocketHeaderTemplate). But instead I see my core data of
Row 1
Row 2
Row 3
This seems to indicate that my overriding datatemplateselector is not being hit (indeed if I set a breakpoint in DocketDataTemplateSelector, at no time do I see it being hit). Where am I going wrong with this?
Thanks

Answer 1

Sorry i can not post this as comment, i haven't got enough score.
I just tried your example code (my first VB project) and guess what, it works as expected: three times "Header Row Test" on yellow background. I've put the ListBox in a Grid in the UserControl, then put the UserControl in a Grid in a Window, then set the DataContext of the UserControl to a ViewModel object with your TestData property.
Something must be wrong that is not demonstrated by your example code, maybe you can provide more info.