Problem while setting the webdynpro alv table column set size

Dear Dynpro guru's,

  i'm facing problem while setting the fix length of the alv Webdynpro table that one is my table column is not visible while i'm using the below code.

  LO_CMP_USAGE =   WD_THIS->WD_CPUSE_ALV( ).

    IF LO_CMP_USAGE->HAS_ACTIVE_COMPONENT( ) IS INITIAL.

     LO_CMP_USAGE->CREATE_COMPONENT( ).

    ENDIF.

   LO_INTERFACECONTROLLER =   WD_THIS->WD_CPIFC_ALV( ).

   LV_VALUE = LO_INTERFACECONTROLLER->GET_MODEL( ).

   LV_VALUE->IF_SALV_WD_TABLE_SETTINGS~SET_WIDTH( '500' ).

LR_TABLE_SETTINGS ?= LV_VALUE.

LR_COLUMN = LV_VALUE->IF_SALV_WD_COLUMN_SETTINGS~GET_COLUMN( 'SNO' ).

LR_COLUMN->SET_WIDTH( '20' ) .

LR_TABLE_SETTINGS->SET_FIXED_TABLE_LAYOUT( ABAP_TRUE ).

Please help me to this situation .

Thanks & Regards,

Suresh Reddy