How to sort a ListView in ascending or descending order by a given column?
Sorting a TListView by the column clicked by the user
We want the following behaviour for a ListView:
When the user clicks on a column header, the ListView should be sorted by that column
The initial sort order should be ascending. If the user clicks on the same column again, the sort order should be toggled. If the user clicks on another column, the sort order of the new column should be the same as the last sorted column.
For the implementation we need two variables to hold the last column clicked by the user and the current sort order:
var
LastSortedColumn: integer;
Ascending: boolean;
We can initialize them when the form is created:
procedure TForm1.FormCreate(Sender: TObject);
begin
LastSortedColumn := -1;
Ascending := True;
end;
In the ColumnClick event of the ListView we determine the sort order and perform the sort:
procedure TForm1.ListView1ColumnClick(Sender: TObject;
Column: TListColumn);
begin
if Column.Index = LastSortedColumn then
Ascending := not Ascending
else
LastSortedColumn := Column.Index;
TListView(Sender).CustomSort(@SortByColumn, Column.Index);
end;
SortByColumn is a function that should be previously declared and is the function used by CustomSort to compare two items. The value passed to the Data parameter of CustomSort will be passed as the Data parameter to SortByColumn and we use it for the sort column:
function SortByColumn(Item1, Item2: TListItem; Data: integer):
integer; stdcall;
begin
if Data = 0 then
Result := AnsiCompareText(Item1.Caption, Item2.Caption)
else
Result := AnsiCompareText(Item1.SubItems[Data-1],
Item2.SubItems[Data-1]);
if not Ascending then Result := -Result;
end;