Well, I didn't finish up extending the Spinner class. That's an exercise for another day. But I have managed to make the Save Game form in PCDB SuDoku Solver provide a pretty similar interface to a Windows ComboBox. Here's an example.
You can touch a field such as Source and select an item from the drop-list that drops down. If the entry you want isn't in the list, touch the "+" button and then you can type the new value into a field in the same place on the screen. Touch "Done" on the virtual keyboard and hey presto! The new item is added to the drop-down list and automatically selected as the value in the field.
It should be possible to package all of that up in a Class, and I may do that in the future once the app is out there in the market.
All the screen shots in the User Guide and Help Files are now up to date with the latest changes to PCDB SuDoku Solver, and the User Guide in PDF form is available on this website.