Hi,
have you tried something like this:
DATA lo_barc_control TYPE REF TO cl_gui_barchart.
DATA lo_gui_control TYPE REF TO cl_gui_control.
DATA lv_height TYPE i.
lo_barc_control->get_parent( IMPORTING parent = lo_gui_control ).
lo_gui_control->get_height( IMPORTING height = lv_height ).
Thx.