I know what you are trying to do. Often the data shown is not what is stored in the table. I use arrays for my listbox and include an extra column (not displayed) to contain the key value. The listbox array is loaded by the init method and the validate method creates keys for new data entered. A listbox property is set to the column number that contains the key and an line has to be added to the save operation to get the listbox key value.

My listbox class has a few other methods for house keeping, I've used this approach for years.