Re: ? Extending and (Forcibly?) Overriding a Class

"Doug Harrison [MVP]" <>
Tue, 02 Dec 2008 19:51:02 -0600
On Tue, 2 Dec 2008 20:08:03 -0500, "Alec S." <nospam@> wrote:

I didn?t override InsertColumn. Instead I made a separate function like you
suggested earlier:

 LRESULT CCustList::OnInsertColumn(WPARAM wParam, LPARAM lParam) {
    int nCol=(int)wParam;
    const LVCOLUMN* pCol=(const LVCOLUMN*)lParam;
    LRESULT lRet=InsertCColumn(nCol, &Col);
  return lRet;

 int CCustList::InsertCColumn(int nCol, const CLVCOLUMN* pColumn) {
  //store pColumn->iDataType and pColumn->iWidthType somewhere
  int ret =DefWindowProc(LVM_INSERTCOLUMN, (WPARAM)nCol,
  return ret;

This way, I can specifically call InsertCColumn with the new struct that has the
extra info, and any calls to the original handler will use the default settings
for the extra info.

It?s working so far, and the logic seems sound as far as I can tell.

It's sort of backwards for a member function like InsertCColumn to call
DefWindowProc. What if a derived class handled LVM_INSERTCOLUMN? You would
bypass it completely. I would do it the way I suggested with the using
declaration and overloading. The functions would look something like this:

int CCustList::InsertColumn(
      int nCol,
      const LVCOLUMN& colData,
   InsertColumn(nCol, &colData); // Or whatever the parameters are...
   // ...Don't forget to check for errors, update nCol if necessary, etc!
   SetColumnInfo(nCol, extra_params);

LRESULT CCustList::OnInsertColumn(WPARAM wParam, LPARAM lParam)
    int nCol = (int) wParam;
    const LVCOLUMN* pCol = (const LVCOLUMN*) lParam;
   // Use the first of the following two lines if OnInsertColumn is
   // defined by CListCtrl, the second if it is not.
   // Don't forget to check for errors, update nCol if necessary, etc!
   LRESULT lRet = CListCtrl::OnInsertColumn(...);
   LRESULT lRet = Default();
   SetColumnInfo(nCol, defaults);
   return lRet;

I just need to figure out where to store the extra information (I?m looking for
where the column text, width, etc. are stored; I still believe they are stored
in the header, not the list control):

I already tried that, but there is no information on the relation between a
CListCtrl?s InsertColumn() its CHeaderCtrl. :(

The next place to look would be the Windows SDK documentation. See if the
header and/or listview controls maintain a "user data" field for each
column. It would be big enough to store a pointer, which means you can
store pointers to objects of arbitrary size, though dynamically allocating
them means extra work when time comes to delete them. Usually there's a
"delete item" message you can handle. If there is no such field, you will
have to maintain a parallel array containing the extra info. Oh wait,
looking at some of my old code, the HDITEM struct contains an lParam member
you can use however you like, such as storing a pointer there. So you need
to retrieve the header control and store your extra data there using

Doug Harrison
Visual C++ MVP

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