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 );


 

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