WPF ComboBox ItemTemplateSelector.Selecttemplate is never called - wpf

Question

Based on this answer I tried to use the following code to achieve a ComboBox with different templates depending on whether or not the drop down is open.
The ComboBox definition looks like this:
<ComboBox SelectedValuePath="Id"
DisplayMemberPath="Name">
<ComboBox.Resources>
<DataTemplate x:Key="SelectedTemplate">
<TextBlock Text="Abbreviation" />
</DataTemplate>
<DataTemplate x:Key="DropDownTemplate">
<ContentControl Content="{Binding}">
<ContentControl.Style>
<Style TargetType="{x:Type ContentControl}">
<Setter Property="ContentTemplate">
<Setter.Value>
<DataTemplate>
<Grid Width="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Border}}, Path=ActualWidth, Mode=OneTime}">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*" />
<ColumnDefinition Width="20" />
</Grid.ColumnDefinitions>
<TextBlock Grid.Column="0"
Text="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type ComboBox}}, Path=DisplayMemberPath}" />
<TextBlock Grid.Column="1"
Text="Abbreviation" />
</Grid>
</DataTemplate>
</Setter.Value>
</Setter>
</Style>
</ContentControl.Style>
</ContentControl>
</DataTemplate>
<infrastructure:ComboBoxItemTemplateSelector x:Key="ComboBoxItemTemplateSelector"
DropDownDataTemplate="{StaticResource DropDownTemplate}"
SelectedDataTemplate="{StaticResource SelectedTemplate}" />
</ComboBox.Resources>
</ComboBox>
and the ComboBoxItemTemplateSelector looks like this:
public class ComboBoxItemTemplateSelector : DataTemplateSelector
{
public DataTemplate DropDownDataTemplate { get; set; }
public DataTemplate SelectedDataTemplate { get; set; }
public override DataTemplate SelectTemplate(object item, DependencyObject container)
{
return DependencyObjectHelper.GetVisualParent<ComboBoxItem>(container) != null ? this.DropDownDataTemplate : this.SelectedDataTemplate;
}
}
Now the problem is that somehow SelectTemplate is never called, even although I checked all the DynamicResources and StaticResources.

Answer 1

You need to assign the ComboBoxItemTemplateSelector to the ComboBox like this:
<ComboBox ItemTemplateSelector="{DynamicResource ComboBoxItemTemplateSelector}">
and you cannot set the DisplayMemberPath or the SelectTemplate method will never be called.