1.  Created a package in Program Units called FLEXFIELDS:

PACKAGE FLEXFIELDS IS
  PROCEDURE Define(p_insert in varchar2, p_update in varchar2, p_read_only in varchar2);
  PROCEDURE Define_dff_for_quotation_tab(p_insert in varchar2, p_update in varchar2, p_read_only in varchar2);
  PROCEDURE Define_dff_item_master(p_insert in varchar2, p_update in varchar2, p_read_only in varchar2);
  PROCEDURE Define_dff_item_master_org(p_insert in varchar2, p_update in varchar2, p_read_only in varchar2);
END;

Package Body:  (I purposely left my commented code in so you can see what else can be added):

PACKAGE BODY FLEXFIELDS IS
PROCEDURE Define(p_insert in VARCHAR2, p_update in VARCHAR2, p_read_only in VARCHAR2) IS
  BEGIN
     FND_DESCR_FLEX.DEFINE(block => 'QP_LIST_LINES_V',
                field => 'DF',
                appl_short_name => 'QP',
                DESC_FLEX_NAME => 'QP_LIST_LINES'
--          ,
--          code => 'COST',
--          num => Structure_Number,
--          description => 'DESC_FLEX_DESCRIPTION',
--          id => 'COST_ALLOCATION_KEYFLEX_ID',
--          data_field => 'CONCATENATED_SEGMENTS',
--          validate =>'FULL',
--          vdate => to_char(sysdate),
--          required => 'Y',
--          allownulls => 'N',
--  usedbflds => 'Y',
--          query_security => 'N',
--          where_clause => 'summary_flag != ''Y''',
--          insertable=>p_insert,
--          updateable=>p_update,
--  displayable=>'ALL\\09\\010\\011',
--          title=>'Additional Info for List Lines'
);
  END;

PROCEDURE Define_dff_for_quotation_tab(p_insert in VARCHAR2,
   p_update in VARCHAR2,
   p_read_only in VARCHAR2) IS
  BEGIN
     FND_DESCR_FLEX.DEFINE(block => 'SUPPLIER_QUOTATION',
                field => 'DF',
                appl_short_name => 'PO',
                           DESC_FLEX_NAME => 'PO_LINES');
  END;

PROCEDURE Define_dff_item_master(p_insert in VARCHAR2,
    p_update in VARCHAR2,
    p_read_only in VARCHAR2) IS
  BEGIN
    FND_DESCR_FLEX.DEFINE(BLOCK=>'ITEM_FLEXFIELDS_GLO',
          FIELD=>'DF',
          APPL_SHORT_NAME=>'INV',
          DESC_FLEX_NAME=>'MTL_SYSTEM_ITEMS'
       );
  END;
 

PROCEDURE Define_dff_item_master_org(p_insert in VARCHAR2,
                                     p_update in VARCHAR2,
        p_read_only in VARCHAR2) IS
  BEGIN
    FND_DESCR_FLEX.DEFINE(BLOCK=>'ITEM_FLEXFIELDS_ORG',
          FIELD=>'DF',
          APPL_SHORT_NAME=>'INV',
          DESC_FLEX_NAME=>'MTL_SYSTEM_ITEMS'           );
  END;
END;

2. Added this code to form level WHEN-NEW-FORM-INSTANCE trigger:

DECLARE
  f_insert VARCHAR2(80);
  f_update VARCHAR2(80);
  f_read_only VARCHAR2(80);

BEGIN
f_insert := '';
f_update := '';
f_read_only := 'N';

flexfields.define(f_insert, f_update, f_read_only);
flexfields.Define_dff_for_quotation_tab(f_insert, f_update, f_read_only);
flexfields.Define_dff_item_master(f_insert, f_update, f_read_only);
flexfields.Define_dff_item_master_org(f_insert, f_update, f_read_only);

END;

3. Now the blocks and fields have to match what you set up in your procedures.

Example – the last procedure from above shows:

  BEGIN
    FND_DESCR_FLEX.DEFINE(BLOCK=>'ITEM_FLEXFIELDS_ORG',
          FIELD=>'DF',
         APPL_SHORT_NAME=>'INV',
          DESC_FLEX_NAME=>'MTL_SYSTEM_ITEMS'   (etc., etc.)

So In your data block, ITEM_FLEXFIELDS_ORG, you have to have a field called DF.  Add The following trigger to this item:
 
WHEN-VALIDATE-ITEM  (containing this code à fnd_flex.event('WHEN-VALIDATE-ITEM');)
WHEN-NEW-ITEM-INSTANCE (containing this code à fnd_flex.event('WHEN-NEW-ITEM-INSTANCE);)

4. Make the “DF” Item in your Data Block(s) visible on appropriate canvas/tab page.

With Compliments from: Matt Kelly

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