CListCtrl LVN_ITEMCHANGING

[Oliver Twesten]

hi @all

I want to handle the LVN_ITEMCHANGING notification for one of my CListCtrl (Report Style) to prevent change of item focus. According to MSDN, returning *pResult = TRUE from the LVN_ITEMCHANGING notification handler should prevent the change.

Problem: When I try to change the item focus by mouse and display a (Afx)MessageBox(...) within the LVN_ITEMCHANGING handler function, the message is received a 2nd time as soon as the mouse is moved.
This does not occur when either (a) I change the focus item with the cursor-keys on the keyboard or (b) I don't display a message box.

You can breakpoint in the notification handler and see, that the pNMListView data is excatly the same for the doubled message.

This is the relevant code:

void CListCtrl_LVN_ITEMCHANGINGDlg::OnItemChangingList1(NMHDR* pNMHDR, LRESULT* pResult) 
{
	NM_LISTVIEW* pNMListView = (NM_LISTVIEW*)pNMHDR;

	// check for change of LVIS_FOCUSED state
	if ( (pNMListView->uChanged == LVIF_STATE) && (pNMListView->uOldState == LVIS_FOCUSED) )
	{
		// display message box
		AfxMessageBox("Item change not allowed.");

		// disallow itemchange
		*pResult = TRUE;
	}
	else
	{
		// allow itemchange
		*pResult = FALSE;
	}
}




void CListCtrl_LVN_ITEMCHANGINGDlg::OnItemChangingList2(NMHDR* pNMHDR, LRESULT* pResult) 
{
	NM_LISTVIEW* pNMListView = (NM_LISTVIEW*)pNMHDR;
	
	// check for change of LVIS_FOCUSED state
	if ( (pNMListView->uChanged == LVIF_STATE) && (pNMListView->uOldState == LVIS_FOCUSED) )
	{
		// play sound
		MessageBeep(MB_ICONEXCLAMATION);

		// disallow itemchange
		*pResult = TRUE;
	}
	else
	{
		// allow itemchange
		*pResult = FALSE;
	}
}

I've also built a small demo project (dialog based) you may want to download and have a look into.

Any suggestions are greatly appreciated! Thank you!

Oliver.