In field definitions, validation tab, select "Member of a Value List" and select the value list in the dropdown. This will make it so that users cannot enter any data in the field that is in the value list.
Hope this helps.
Set a script trigger on the dropdown using On Object Keystroke - have it run a one-line script that says:
Exit Script[Result: False]
The cursor will still show up, but you won't be able to type anything with this trigger active.
All FMP dropdowns have what I consider to be a bug which is if you select a value from the list, then click the cursor into the middle of that value, and then select a different value from the list, the 2 values will get concatenated at the cursor's location. Better to use popups.
Tried both, with the "On Object Keystroke Script". It's is exactly what I was looking for. The script prevents any entering of non drop down list data.....
Prior to the change, there were several occasions where the data would be accidentally entered and a cross between the drop down list value and accidental key stokes. It looked very untidy...