Late binding of image – I_IMAGECALLBACK

When inserting an item in the list view control, you dont

have to specify the image just then. You can delay a decision on the image

by using a callback item. A callback item is an item that causes the list

view control to send the LVN_GETDISPINFO notification to its parent whenever

it needs information to display the item. The LVN_GETDISPINFO notification

can be handled by the parent window or it can be reflected back to the

list view control, the latter solution being the more preferred. Here are

the steps to use message reflection.

• 
  Add a message handler for =LVN_GETDISPINFO in your CListCtrl derived class.
  The = sign indicates that it is a reflected message. This adds a line
  in the message map section which looks like

ON_NOTIFY_REFLECT(LVN_GETDISPINFO, OnGetDispInfo)

• 
  Implement the message handler. The message handler shown below does not
  show any logic to decide on the image index. The image index would most
  likely be a function of the item index and/or the items data (pItem->lParam).

void CMyListCtrl::OnGetDispInfo(NMHDR* pNMHDR, LRESULT* pResult) 
{ 
        LV_ITEM *pItem = &((LV_DISPINFO*)pNMHDR)->item; 

        if( pItem->mask & LVIF_IMAGE ) 
        { 
                // GetImageFor() needs to be defined and should return image number 
                pItem->iImage = GetImageFor( pItem-> iItem); 
        } 
       
        *pResult = 0; 
}

 


• 
  Insert items using the I_IMAGECALLBACK value for image index. E.g.

m_listctrl.InsertItem( nRow, sItemText, I_IMAGECALLBACK );