Advanced MFC Programming

Chapter 14. Views
When the list items are displayed in “Report” style, one thing we can implement is to sort all the files
by different attributes. For example, if we click on “Name” column, all the files should be sorted by their
names; if we click on “Size” column, all files should be sorted by their sizes; if we click on “Type” column,
all the files should be sorted by their extensions; if we click on “Updated” column, all the files should be
sorted by their updated dates and times.
Sort Related Functions
We can call function CListCtrl::SortItems(…) to implement item sorting. This function has two
parameters:
BOOL CListCtrl::SortItems(PFNLVCOMPARE pfnCompare, DWORD dwData);
The function’s first parameter is a little special, which is the pointer to a callback function provided by
the programmer. The callback function will be used to perform actual comparison. This is because when
comparing two items, class CListCtrl has no way of knowing which item should precede the other. In
order to provide our own rules of making comparison, we need to implement the callback function.
The callback function has the following format:
int CALLBACK CompareFunc(LPARAM lParam1, LPARAM lParam2, LPARAM lParamSort);
In order to compare two items, we need to provide each item with a parameter, which is an LPARAM
type value. When two items are compared, their parameters will be passed to the callback function, which
will return different values indicating which item should precede the other. If the first item (whose
parameter is lParam1) should precede the second item (whose parameter is lparam2), the function needs to
return -1; if the first item should follow the second item, the function needs to return 1; if the two items are
equal, the function needs to return 0.
When calling function CListView::SortItems(…), we can pass different pre-defined values to
parameter dwData, which will be further passed to parameter lParamSort of the callback function. This
provides us with a way of specifying different types of sorting methods.
Adding Parameters to Items
By now, when creating an item, we did not specify any parameter for it. Actually, any item in the list
control can store a 32-bit parameter which can be used to distinguish one item from another. Of course the
item index can also be used for this purpose. However, since the relative positions of two items can change
frequently, the index of an item is also not fixed. Since the only information passed to the callback function
about an item is its parameter, we must make it unique for any item.
In the sample, function CBrowserView::ChangeDir() is customized as follows: when a new item is
added to the list control, we set its parameter to its initial index and use it as the identification of this item.
This parameter will not change throughout its lifetime:
……
……
lvi.mask=LVIF_TEXT | LVIF_IMAGE | LVIF_PARAM;
lvi.iItem=i;
lvi.iSubItem=0;
lvi.pszText=(LPSTR)(const char *)szFileName;
lvi.lParam=(LPARAM)i;
Functions Implementing Comparisons
Four static member functions are implemented for doing different types of comparisons:
static int CExplorerView::CompareByName(LPARAM, LPARAM, CListCtrl &);
static int CExplorerView::CompareBySize(LPARAM, LPARAM, CListCtrl &);
static int CExplorerView::CompareByType(LPARAM, LPARAM, CListCtrl &);
static int CExplorerView::CompareByDate(LPARAM, LPARAM, CListCtrl &);
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