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 );