Question

Just wondering what the difference between MFC control messages prefixed with the following is:

LVN (e.g. LVN_ITEMCHANGED) HDN (e.g. HDN_TRACK) NM (e.g. NM_HOVER) 

Also, I am using a ListControl and trapping when the user clicks on an item using the NM_CLICK message. I also want to trap when a user selects a new item view a key e.g. up/down arrow keys. Can anyone tell me which message I should be trapping for this?

Thanks

Answer 1

For change in selection, you need to handle the LVN_ITEMCHANGED notification:

NMLISTVIEW & nm = *(NMLISTVIEW *) pnmh; if (  (nm.uNewState ^ nm.uOldState) & LVIS_SELECTED)  {         // nm.iItem was selected or deselected    if (!m_internalUIChange)    {       // see below    } } 

The first ‘if’ checks if the ‘selected’ state has changed. Note that, when selecting a different item in the list, this still fires twice: once for the old item to be deselected, and once for the new item to be selected. This is necessary, however, to fetch a ‘complete deselect’.

This notification fires very often – even when you modify the control programmatically. If your handler should react only to user events, you will need at least a flag that you set durign these operations (I use a class together with a RAII-Lock for that, so I don’t forget to reset it)