PRO changefield, base, newfieldname, BOXZOOM = boxzoom
;
   widget_control, base, get_uvalue = top_uvalue
;
; changement de exextra :
   exextra = definedefaultextra(newfieldname)
   specifieid = widget_info(base,find_by_uname = 'specifie')
   widget_control, specifieid, set_value = exextra
; chamgement de variable -> devra-t-on changer de domaine verticale?
   oldzgrid = extractatt(top_uvalue, 'zgrid')
   currentfile = extractatt(top_uvalue, 'currentfile')
   listgrid = (*(extractatt(top_uvalue, 'fileparameters'))[currentfile]).listgrid
   listvar = (*(extractatt(top_uvalue, 'fileparameters'))[currentfile]).listvar
;   for i = 0,  n_elements(listvar)-1 do print,  listvar[i], '/', listgrid[i]
   indexvar = where(listvar EQ newfieldname) & indexvar = 0 > indexvar[0]
   vargrid = strupcase(listgrid[indexvar])
   IF vargrid EQ 'W' then zgrid = 'W' ELSE zgrid = 'T'
   if zgrid NE oldzgrid then BEGIN
      *top_uvalue[1, findline(top_uvalue, 'zgrid')] = zgrid
      if NOT keyword_set(boxzoom) THEN BEGIN
         widget_control, widget_info(base, find_by_uname = 'domain'), get_value = boxzoom
         widget_control, widget_info(base, find_by_uname = 'domain'), set_value = boxzoom
      endif
   endif
;
   return
end