How to override PreviewKeyDown on a TextBox? - wpf

Question

I have a handler for the PreviewKeyDown event on a TextBox inside a control I made, which checks to see if the user has pressed the down key. The event handler correctly handles the key press when the control sits inside a layout container like a grid. If however, I place the control inside a DataGrid's DataGridTempalteColumn, the control does not do what I need it to do.
I think the issue is that because the PreviewKeyDown is on a Tunneling strategy, the host DataGrid gets to handle the down arrow key press before my control does. For the down arrow the DataGrid moves the focus to the next row. The DataGrid doesn't seem to be setting the IsHandled to true, because it the event eventually gets down to my control, but it does nevertheless do its own thing on the event, which breaks things for me.
The issue isn't really with the DataGrid, but with the fact that my control has a tunneling PreviewKeyDown event from the TextBox. I'm looking for a way to override this default event on the TextBox. Perhaps there's something I can do with attached behaviors? Maybe I need to inherit from the TextBox and then override? So far I've not found anything that indicates how to handle a situation like this.
Below is the original text for this question that didn't yield any answers
I'm having difficulty using a custom autocomplete text box I made as a DataTemplate in a DataGridTemplateColumn.
<DataGrid.Columns>
<DataGridTemplateColumn Header="Material" Width="300">
<DataGridTemplateColumn.CellEditingTemplate>
<DataTemplate>
<local:actextbox Text="{Binding Path=Description, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}"
MatchList="{Binding Path=DataContext.LaborTemplatesList, RelativeSource={RelativeSource AncestorType=UserControl, AncestorLevel=2}}"/>
</DataTemplate>
</DataGridTemplateColumn.CellEditingTemplate>
<DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<TextBlock Text="{Binding Path=Description}"/>
</DataTemplate>
</DataGridTemplateColumn.CellTemplate>
</DataGridTemplateColumn>
</DataGrid.Columns>
The actextbox class derives from user control and has event handlers to respond to certain key presses like so
private void myTextBox_PreviewKeyDown(object sender, KeyEventArgs e)
{
if (e.Key == Key.Down & myPopup.IsOpen == true)
{
myPopUpList.SelectedIndex = 0;
ListBoxItem lbi = (ListBoxItem)myPopUpList.ItemContainerGenerator.ContainerFromItem(myPopUpList.SelectedItem);
lbi.Focus();
e.Handled = true;
}
}
The intent is that when an autocomplete popup is displayed, pressing down and up allows the user to navigate its contents. This works as expected when the control is placed in a hierarchy of layout containers; however, when it is part of the cell in a datagrid the expected behaviour is lost. Looks like the previewKeyDown is used by the DataGrid to apply its own interpretation of the down or up arrows, and while it does not set the event as handled, by the time the event gets down to my control focus is lost, and different row is selected.
I've looked online all over, and wasn't able to find any clues on how to handle this. Certainly, I've seen controls inside DataGridTemplateColumns handle all sorts of inputs, but how they accomplish this is lost on me.

Answer 1

OK, following some advice to use Snoop I figured out what was happening. In fact the issue was not that the DataGrid was doing something with the PreviewKEyDown event, but that I was moving focus away from the data grid cell that was presently being edited triggering a CellEditEnding event. This resulted in the behaviour I was observing.