If they type in 1.5 and then come back into edit mode, when XamMultiColumnComboEditor calls Loaded, I pipe the text into the SpecializedTextBox for the XamMultiColumnComboEditor editor.

As for your sample, I see things working correctly in the sample and now I need to get it working properly in my real project.

Were you able to find out what was going on with the weird blue box that would show up in the popup when typing when a footer is present?

Thanks for explaining that.  It makes sense that you would have to reassign the ItemsSource if the values in it are dependent on other columns.  I'm not sure how you plan to handle persisting newly added items though.  For example if I type in 1.5 and then tab to the next column but then go back to the previous column and enter edit mode again, I would expect to still see 1.5 in the dropdown list since that's what CustomValueEnteredAction="Add" would do.  Unless you just need that setting to allow users to type whatever they want into the textbox and not actually need the value to be persisted.  In which case then forget everything I was confused about.

Thanks for getting back to me.

I haven't looked at your sample yet, but to answer your question:

DropDownValues is created based on what the values are in other columns, so it needs to be recreated whenever a value changes anywhere in the row.  So I suppose I could persist it and try to be smarter about when the other values are dirty, but even then I would need one for each cell, so having those always ready would increase my program's memory footprint.  I am just adding them to the collection so it is a valid selection that gets sent back to the textbox mode when the cell is not in edit mode, so if you have a better solution for that I am all ears.  

Hi Jon,

The editor's value was not getting set for some reason so I modified the code to handle the combo editor's SelectionChanged event.  This event is firing when you press Enter/Tab or click away from the editor when there is text in the combo editor (since the "Add" modifier is on).  Once a selection is made I am getting the cell and setting it's Value directly.  One thing I'm confused about is the way that you are setting the DropDownValues collection.  The code is currently setting this every time edit mode is started on the cell so I would think that any additions you add to the dropdown list would be lost when you entered edit mode on that cell again.  Wouldn't you want to persist the collection rather than resetting it constantly?