Sorting a TListView by the column clicked by the user (Views: 29)
Problem/Question/Abstract: How to sort a ListView in ascending or descending order by a given column? Answer: Solve 1: 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; Solve 2: Instead of calling the custum sort procedure we also can use the OnColumnClick and the OnCompare events ion conjunction... That way the compare routine is kept within the class, here a TForm decedant. Like this: procedure TfrmMain.lvThingyColumnClick(Sender: TObject; Column: TListColumn); begin if Column.Index = fColumnClicked then fSortAscending := not fSortAscending else begin fSortAscending := true; fColumnClicked := Column.Index; end; // else Screen.Cursor := crHourglass; try (Sender as TListView).AlphaSort; finally Screen.Cursor := crDefault; end; // try end; procedure TfrmMain.lvThingyCompare(Sender: TObject; Item1, Item2: TListItem; Data: Integer; var Compare: Integer); begin case fColumnClicked of 0: Compare := CompareStr(Item1.Caption, Item2.Caption); else Compare := CompareStr(Item1.SubItems[fColumnClicked - 1], Item2.SubItems[fColumnClicked - 1]); end; // case if not fSortAscending then Compare := -Compare; end; |