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procedure TForm1.Panel1DragDrop(Sender, Source: TObject; X, Y: Integer);
var
  Temp: TListBox;
begin
  Temp := (Source as TListBox);
  Panel1.Caption := Temp.Items[Temp.ItemIndex];
end;

procedure TForm1.Panel1DragOver(Sender, Source: TObject; X, Y: Integer;
  State: TDragState; var Accept: Boolean);
begin
  Accept := Source = ListBox1;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  ListBox1.DragMode := dmAutomatic;
end;