In the Free text invoice form (CustFreeInvoice) there is an interesting GUI trick that I would like to completely understand and perhaps replicate.
The Number sequence group field in the Header's General tab first appears as a FormStringControl, but when it is selected for editing it transforms to a ComboBox to properly serve the corresponding foreign key field.
I guess this is happening for performance reasons, i.e. to avoid unnecessary ComboBox lookup initialization when the field is not going to be used; is that right?
I found the FormStringControl created under TabMain / TabPageDetails / TabDetails / HeaderViewTabPage / FastTab / InvoiceFastTab / GroupPosting group; but I wasn't able to locate the ComboBox definition.
Any idea on how the ComboBox control is instantiated, how this mechanism works and how to replicate it?
