CListCtrl.SortItems question...

CListCtrl.SortItems(CompareFunc, dwData)
int CALLBACK CompareFunc(LPARAM lParam1, LPARAM lParam2, LPARAM lpara);

I use debugger to step inside the 'CompareFunc' and find out
lParam1 and lParam2 are both 0!!!!! However, lpara has the correct value. WHY????
stephenkongAsked:
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Answers2000Commented:
lParam1 and lParam2 are the item data associated with the two items being compared.

If you don't set item data then it's zero

To set item data with an item - use SetItemData member of CListCtrl.

The normal way way to do this is
1. In dwData pass a "pseudo" this ptr to the class
SortItems( CompareFunc, (LPARAM)this ) ;

2. In CompareFunc convert this back to a CListCtrl *, or a ptr to your derived class
int CALLBACK CompareFunc(LPARAM lParam1, LPARAM lParam2, LPARAM lpara)
{
 CListCtrl * pList = (CListCtrl *)lpara ;
}

3. To get non-zero item data
EITHER
(a) Set the row-id as item data for each item in the list before doing SortItems - then in CompareFunc you the item data as a param to GetItemText
OR
(b) Set the item data to point to some structure (you allocate) containing comparison data which the sort function uses

4. BTW if you want CompareFuncs to be a class member, make it a static member


Here's an example - that uses method 3(b).  Previous to this I have set item data with a record id for an AAInfo record (which is my data structure).  GetAA is a function I wrote to get an AAInfo record.  m_nSortColumn and m_bSortReverse are an int and BOOL class member

void CTComply::SortList()
{
      CWaitCursor oWait ;
      m_list.SortItems( CTComply::CompareFunc, (DWORD)this ) ;
}

nt CALLBACK CTComply::CompareFunc(LPARAM lParam1, LPARAM lParam2, LPARAM lParamSort)
{
      CTComply * pComply = (CTComply *)lParamSort ;
      ASSERT_VALID( pComply ) ;

      AAInfo oInfo1 ;
      AAInfo oInfo2 ;

      // get 2 items
      VERIFY( GetAA( lParam1, oInfo1 ) ) ;
      VERIFY( GetAA( lParam2, oInfo2 ) ) ;


      // now get 2 strings
      CString str1 ;
      CString str2 ;

      switch ( pComply->m_nSortColumn )
      {
      default :
      case 0 :
            str1 = oInfo1.m_strManufacturer ;
            str2 = oInfo2.m_strManufacturer ;
            break ;

      case 1 :
            str1 = oInfo1.m_strProduct ;
            str2 = oInfo2.m_strProduct ;
            break ;

      case 2 :
            str1 = oInfo1.m_strVersion ;
            str2 = oInfo2.m_strVersion ;
            break ;

      case 3 :
            str1 = oInfo1.m_strProductType ;
            str2 = oInfo2.m_strProductType ;
            break ;

      case 4 :
            str1 = oInfo1.GetStatus() ;
            str2 = oInfo2.GetStatus() ;
            break ;
      }


      // do comparison
      int nn = 0 ;

      if ( str1 < str2 ) nn = -1 ;
      if ( str1 > str2 ) nn = 1 ;

      if ( pComply->m_bSortReverse )
      {
            nn = 0 - nn ;
      }

      return nn ;
}

void CTComply::OnColumnclickList1(NMHDR* pNMHDR, LRESULT* pResult)
{
      NM_LISTVIEW* pNMListView = (NM_LISTVIEW*)pNMHDR;

      int nNewHeader = pNMListView->iSubItem ;

      if ( nNewHeader == m_nSortColumn )
      {
            m_bSortReverse = !m_bSortReverse ;
      }
      m_nSortColumn = nNewHeader ;
      SortList() ;

      *pResult = 0;
}





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