Advanced MFC Programming

Chapter 14. Views
Actually, in the callback function, one of the above functions is called to perform the comparison
according to parameter lParamSort:
int CALLBACK CExplorerView::CompareFunc
(
LPARAM lParam1, LPARAM lParam2, LPARAM lParamSort
)
{
CListCtrl &lc=
(
(CExplorerDoc *)
(
((CMainFrame *)(AfxGetApp()->m_pMainWnd))->GetActiveDocument()
)
)->GetCExplorerView()->GetListCtrl();
switch((int)lParamSort)
{
case 0:
{
return CompareByName(lParam1, lParam2, lc);
break;
}
case 1:
{
return CompareBySize(lParam1, lParam2, lc);
break;
}
case 2:
{
return CompareByType(lParam1, lParam2, lc);
break;
}
case 3:
{
return CompareByDate(lParam1, lParam2, lc);
break;
}
}
}
return 0;
Please note that the callback function must be either a global function or a static member function. So
within it we cannot call CListView::GetListCtrl() directly to obtain the list control. Instead, we must
first obtain the current instance of list view, then use it to call function CListView::GetListCtrl() and
obtain the list control. This is why at the beginning of the callback function the current active document is
first obtained, from which the current active list view (and the list control) is obtained.
Using Parameter to Find an Item
Within the function that implements comparison, the only information we know about an item is its
parameter. This is not enough for making comparison. We need to obtain the item and get more
information (In our sample, this includes file name, extension, type, and updated time) before proceeding to
compare the two items.
An item can be obtained from its parameter by calling function CListCtrl::FindItem(…). In order to
call this function, we need to stuff a LV_FINDINFO type object specifying what information is provided for
item searching. To search an item by its parameter, we need to set LVFI_PARAM bit of member flags of the
structure, and assign the parameter to member lParam. In the sample, a static member function
CExplorerView::FindItem(…) is implemented, it can be called from any static member function to find an
item using its parameter:
int CExplorerView::FindItem(LPARAM lParam, CListCtrl &lc)
{
LV_FINDINFO lvfi;
451