TCustomListView.OnCompare Event

Occurs when two items need to be compared during a sort of the list.

Pascal

property OnCompare: TLVCompareEvent;

C++

__property TLVCompareEvent OnCompare;

Description

Write an OnCompare event handler to implement a sort order for the list. An OnCompare event handler is called when the SortType property is stData or stBoth, when the AlphaSort method is called, or when the CustomSort method is called without a SortProc parameter.

The OnCompare event handler compares the list items passed as the Item1 and Item2 parameters. If Item1 is the same as Item2 in the sort order, set the Compare parameter to 0. If Item1 is less than Item2, set the Compare parameter to a value less than 0. If Item1 is greater than Item2, set the Compare parameter to a value greater than 0.

The Data parameter is 0 when the event handler is called to maintain the sort order of a list view with a SortType of stData or stBoth. Similarly, when OnCompare occurs in response to the AlphaSort method, the Data parameter is 0. When OnCompare occurs in response to the CustomSort method, the Data parameter is the value of the LParam parameter of CustomSort.

C++ Examples:

Copy Code

/*
This example shows how to use the OnColumnClick and
OnCompare events of a list view to let users sort the
columns in a report-style list view by clicking on the
column headers. This requires a global variable to keep
track of the column that was clicked.  The OnColumnClick
event handler sets the global variable to indicate the
column to sort and calls AlphaSort:
*/ 
void __fastcall TForm1::FormCreate(TObject *Sender)
{
  TListItem *Item;
  TListColumn *Column;
  const char imagenames[3][20] = {
    "C++ Image", "Borland Image", "Delphi Image"};
  const char Col2Array[3][40] = {
    "Documentation for the C++ icon.", 
    "Borland icon.", "Delphi icon."
    };
  // Create a ListView item for each image in the ImageList
  ListView1->SmallImages = ImageList1;
  ListView1->LargeImages = ImageList1;
  for (int i = 0; i < ImageList1->Count; i++)
  {
    Item = ListView1->Items->Add();
    Item->Caption = imagenames[i];
    Item->ImageIndex = i;
    Item->SubItems->Add(Col2Array[i]);
  }
  // Create two columns to show during viewing as vsReport
  Column = ListView1->Columns->Add();
  Column->Caption = "Column 1";
  Column->Width = 200;
  Column = ListView1->Columns->Add();
  Column->Caption = "Column 2";
  Column->Width = 200;
  ListView1->ViewStyle = vsReport;
}

int ColumnToSort = 0;

/*
The OnColumnClick event handler sets the global variable to
indicate the column to sort and calls AlphaSort:
*/

void __fastcall TForm1::ListView1ColumnClick(TObject *Sender,
      TListColumn *Column)
{
  ColumnToSort = Column->Index;
  dynamic_cast<TCustomListView *>(Sender)->AlphaSort();
}

/*
The OnCompare event handler causes the list view to sort on
the selected column:
*/

void __fastcall TForm1::ListView1Compare(TObject *Sender, TListItem *Item1,
      TListItem *Item2, int Data, int &Compare)
{
  if (ColumnToSort == 0)
    Compare = CompareText(Item1->Caption,Item2->Caption);
  else
  {
    int ix = ColumnToSort - 1;
    Compare = 
      CompareText(Item1->SubItems->Strings[ix], Item2->SubItems->Strings[ix]);
  }
}

Delphi Examples:

Copy Code

{
This example shows how to use the OnColumnClick and
OnCompare events of a list view to let users sort the
columns in a report-style list view by clicking on the
column headers. This requires a global variable to keep
track of the column that was clicked.  The OnColumnClick
event handler sets the global variable to indicate the
column to sort and calls AlphaSort:
} 
var ColumnToSort: Integer;

procedure TForm1.FormCreate(Sender: TObject);
var
  I: Integer;
  ListItem: TListItem;
  NewColumn: TListColumn;
const
  imagenames: Array[0..2] of string = ('C++ Image', 'Borland Image', 'Delphi Image');
begin
  Col2Array[0]:= 'Documentation for the C++ icon.';
  Col2Array[1]:= 'Borland icon.';
  Col2Array[2]:= 'Delphi icon.';
  // Create a ListView item for each image in the ImageList
  with ListView1 do
  begin
    SmallImages := ImageList1;
    LargeImages := ImageList1;
    for I := 0 to ImageList1.Count - 1 do
    begin
      ListItem := Items.Add;
      Listitem.Caption := imagenames[I];
      ListItem.ImageIndex := I;
      Listitem.SubItems.Add(Col2Array[I]);
    end;
    // Create two columns to show during viewing as vsReport
    NewColumn := Columns.Add;
    NewColumn.Caption := 'Column 1';
    NewColumn.Width := 200;
    NewColumn := Columns.Add;
    NewColumn.Caption := 'Column 2';
    NewColumn.Width := 200;
    ListView1.ViewStyle := vsReport;
  end;
end;

procedure TForm1.ListView1ColumnClick(Sender: TObject; Column: TListColumn);
begin
  ColumnToSort := Column.Index;
  (Sender as TCustomListView).AlphaSort;
end;

{
The OnCompare event handler causes the list view to sort on
the selected column:
}
procedure TForm1.ListView1Compare(Sender: TObject; Item1, Item2: TListItem; Data: Integer; var Compare: Integer);
var
  ix: Integer;
begin
  if ColumnToSort = 0 then
    Compare := CompareText(Item1.Caption,Item2.Caption)
  else begin
   ix := ColumnToSort - 1;
   Compare := CompareText(Item1.SubItems[ix],Item2.SubItems[ix]);
  end;
end;
{
Note:   This OnCompare event handler uses the global
CompareText function. An application may want to use
AnsiCompareText, CompareStr, or AnsiCompareStr instead,
depending on whether the comparison should be case-sensitive
and whether the locale should be considered.
}