[TYPO3] Processing input in extension backend form

[Matthias Kurz]

Hi list,

In my extension backend form I have an upload file which name contains
information that I want to analyse and store in different fields of my table
(something like year_title_department.pdf). I understand that I can write a
custom class which evaluates a certain field and changes its value with the
method evaluateFieldValue(). But how do I access the value of another field
of my form before saving? Or am I on the wrong way altogether?

Matthias