Return Code	Significance
0	all OK
1	old button-listener function was overwritten
-1	no button area Id passed

With the help of the button-listener callback function you can react on changes to the local button area structure. The button-listener function is automatically invoked by all functions that change button areas, such as dal_but_cre_sel.

The button-listener function must correspond to the specification void fnc(idb, typ, fnc_nam, par). The parameters are:

• DtvLong idb: Button area Id
• DTV_LAY_LNR_TYP typ: Enumeration type, for button areas DTV_LAY_BUT
• char *fnc_nam: Name of the calling function changing button areas
• DtvLong par: Row of the calling function or 0

If the same listener function is used for all objects (menus, button areas, masks), the enumeration type DTV_LAY_LNR_TYP can be used to determine from which object the listener function was called.