Saturday, April 02, 2005

ListView - Sorting by Number or Date

A lot of people are faced with the challenge of sorting a ListView list by numeric value or date. If you do a search, you'll see all kinds of API re-writes and special functions to make it work.

Of course, DotNet has its own way of doing it which looks equally troubling.

The easiest workaround is simply to change your date format to be YMD but that isn't typically a good solution for US companies or applications that show the long date.

But there's an easier way. It was briefly noted here but I wanted to give VFP developers a very straightfoward example.

Short Answer: Create a new column on the list view with a width of zero. Populate the list with the DTOS or sortable version of the value and then instead of setting the SortKey to the displayed column - set it to the OTHER column instead.

This works like a charm.

Some code (if you will)

In the ColumnClick method of the ListView, put in
LPARAMETER columnheader
IF columnheader.Text = "Date"
THIS.SortKey = columnheader.Index
ELSE
THIS.SortKey = columnheader.index-1
ENDIF

WITH THISFORM.ListView
.ColumnHeaders.Add(,,"FileName",100)
.ColumnHeaders.Add(,,"Date",60)
.ColumnHeaders.Add(,,"RealDate",0)

lo = .ListItems.Add(,"NewFile","New File")
lo.SubItems(1) = DTOC(DATE())
lo.SubItems(2) = DTOS(DATE())
lo = .ListItems.Add(,"OlderFile","Old File")
lo.SubItems(1) = DTOC(GOMONTH(DATE(),-5))
lo.SubItems(2) = DTOS(GOMONTH(DATE(),-5))

lo = .ListItems.Add(,"ROlderFile","Really Old File")
lo.SubItems(1) = DTOC(GOMONTH(DATE(),-12))
lo.SubItems(2) = DTOS(GOMONTH(DATE(),-12))
.View = 3
.Sorted = .T.
ENDWITH

Now a few things to note:
1. ListViews can only show TEXT in their columns. That's why I'm using DTOC which makes it appear in the standard format but then DTOS to put it into a useful SORTABLE format

2. The ColumnClick method shown here is really basic. If you wanted to add support for ascending and descending orders, it might look like this:

Procedure ColumnClick
LPARAMETERS ColumnHeader

IF THIS.sortOrder = 0
THIS.SortOrder = 1 && Descending
ELSE
THIS.SortOrder = 0 && Ascending
ENDIF
IF columnHeader.Text = "Date"
THIS.SortKey = ColumnHeader.Index
ELSE
THIS.SortKey = ColumnHeader.Index - 1
ENDIF

Now if you need to do this for a number, instead of using DTOC and DTOS , just pad the numbers with zeroes.