HI,
AS suggested link by Eitan , refer below code
FORM toggle_mode .
* define local data
DATA: ld_mode TYPE i.
if ( gd_mode = cl_gui_textedit=>true ).
gd_mode = cl_gui_textedit=>false.
else.
gd_mode = cl_gui_textedit=>true.
endif.
CALL METHOD go_textedit->set_readonly_mode
EXPORTING
readonly_mode = gd_mode
EXCEPTIONS
error_cntl_call_method = 1
invalid_parameter = 2
others = 3.
IF sy-subrc <> 0.
* MESSAGE ID SY-MSGID TYPE SY-MSGTY NUMBER SY-MSGNO
* WITH SY-MSGV1 SY-MSGV2 SY-MSGV3 SY-MSGV4.
ENDIF.
ENDFORM. " TOGGLE_MODE