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METHOD HandleEvent( nMsg, nWParam, nLParam ) CLASS TComboBox

   local hWndComboList

   if nMsg == FM_CLOSEUP
      return ::CloseUp()
   endif

   if nMsg == FM_DROPDOWN
      return ::DropDown()
   endif

   if ::hWndComboList == nil .and. IsWindow( hWndComboList := hWndComboList( ::hWnd ) )
      ::hWndComboList = hWndComboList 
      // SetWindowProc( hWndComboList, { || nil } )   // probando la nueva función SetWindowProc()
   endif   

return ::Super:HandleEvent( nMsg, nWParam, nLParam )

#include <windows.h>
#include <hbapi.h>
#include <hbapiitm.h>
#include <hbvm.h>

#if ( defined( _MSC_VER )  && ( _MSC_VER < 1500 ) ) // VC98
   #define GWLP_USERDATA    -21 
   #define GWLP_WNDPROC      -4
   LONG_PTR GetWindowLongPtr( HWND hWnd, int nIndex );
   LONG_PTR SetWindowLongPtr( HWND hWnd, int nIndex, LONG_PTR dwNewLong );
#endif

typedef struct
{
   PHB_ITEM pBlock;
   WNDPROC  pOldProc;
} HB_SUBCLASSED, * PHB_SUBCLASSED;

static LRESULT CALLBACK HB_SubclassedProc( HWND hWnd, UINT message,
                                           WPARAM wParam, LPARAM lParam )
{
   PHB_SUBCLASSED pSubclassed = ( PHB_SUBCLASSED ) GetWindowLongPtr( hWnd, GWLP_USERDATA );

   if( pSubclassed && pSubclassed->pBlock )
   {
      PHB_ITEM pReturn;
      #ifndef _WIN64
         PHB_ITEM phWnd = hb_itemPutNL( NULL, ( long ) hWnd );
         PHB_ITEM pMessage = hb_itemPutNL( NULL, ( long ) message );
         PHB_ITEM pwParam = hb_itemPutNL( NULL, ( long ) wParam );
         PHB_ITEM plParam = hb_itemPutNL( NULL, ( long ) lParam );      
      #else   
         PHB_ITEM phWnd = hb_itemPutNLL( NULL, ( HB_LONGLONG ) hWnd );
         PHB_ITEM pMessage = hb_itemPutNLL( NULL, ( HB_LONGLONG ) message );
         PHB_ITEM pwParam = hb_itemPutNLL( NULL, ( HB_LONGLONG ) wParam );
         PHB_ITEM plParam = hb_itemPutNLL( NULL, ( HB_LONGLONG ) lParam );      
      #endif   
      hb_evalBlock( pSubclassed->pBlock, phWnd, pMessage, pwParam, plParam, NULL );
      hb_itemRelease( phWnd );
      hb_itemRelease( pMessage );
      hb_itemRelease( pwParam );
      hb_itemRelease( plParam );
      pReturn = hb_param( -1, HB_IT_ANY );
      if( HB_IS_NUMERIC( pReturn ) )
         return hb_itemGetNL( pReturn );
   }

   return pSubclassed && pSubclassed->pOldProc ? 
          CallWindowProc( pSubclassed->pOldProc, hWnd, message, wParam, lParam ) :
          DefWindowProc( hWnd, message, wParam, lParam );
}

HB_FUNC( SETWINDOWPROC )
{
   #ifndef _WIN64 
      HWND hWnd = ( HWND ) hb_parnl( 1 );
   #else   
      HWND hWnd = ( HWND ) hb_parnll( 1 );
   #endif   
   PHB_ITEM pBlock = hb_param( 2, HB_IT_BLOCK );

   if( hWnd && pBlock )
   {
      PHB_SUBCLASSED pSubclassed = ( PHB_SUBCLASSED ) GetWindowLongPtr( hWnd, GWLP_USERDATA );

      if( ! pSubclassed )
      {
         pSubclassed = ( PHB_SUBCLASSED ) hb_xgrab( sizeof( HB_SUBCLASSED ) );
         SetWindowLongPtr( hWnd, GWLP_USERDATA, ( LONG_PTR ) pSubclassed );
      }
      else
         hb_itemRelease( pSubclassed->pBlock );

      pSubclassed->pBlock = hb_itemNew( pBlock );
      pSubclassed->pOldProc = ( WNDPROC ) SetWindowLongPtr( hWnd, GWLP_WNDPROC,
                                                            ( LONG_PTR ) HB_SubclassedProc );

      hb_retnl( ( LONG_PTR ) pSubclassed->pOldProc );
   }
   else
      hb_retnl( 0 );
}

HB_FUNC( REMOVEWINDOWPROC )
{
   #ifndef _WIN64 
      HWND hWnd = ( HWND ) hb_parnl( 1 );
   #else   
      HWND hWnd = ( HWND ) hb_parnll( 1 );
   #endif   

   if( hWnd )
   {
      PHB_SUBCLASSED pSubclassed = ( PHB_SUBCLASSED ) GetWindowLongPtr( hWnd, GWLP_USERDATA );

      if( pSubclassed )
      {
         SetWindowLongPtr( hWnd, GWLP_WNDPROC, ( LONG_PTR ) pSubclassed->pOldProc );
         hb_itemRelease( pSubclassed->pBlock );
         SetWindowLongPtr( hWnd, GWLP_USERDATA, 0 );
         hb_xfree( pSubclassed );
      }
   }
}