auto extend a listbox

Presumably the number of items is changed at runtime. I don't know how or when you do this, but after you change the number of items in the listbox's itemlist, check the number of items and ajust the height of the listbox.

Sample program: form, listbox1, botton1, botton2,

Just two onclick events



procedure TForm1.Button1Click(Sender: TObject);
begin
  listbox1.Items.Add('test');
  if listbox1.Items.Count > 10 then
    listbox1.Height := 10 * listbox1.ItemHeight + 5
  else
    listbox1.Height := listbox1.Items.Count * listbox1.ItemHeight + 5;
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  listbox1.Items.Delete(1);
  if listbox1.Items.Count > 10 then
    listbox1.Height := 10 * listbox1.ItemHeight + 5
  else
    listbox1.Height := listbox1.Items.Count * listbox1.ItemHeight + 5;
end;

Simple but effective

You cal also use this approach.
Set the ListBox style to lbOwnerDrawFixed

then

procedure TForm1.ListBox1DrawItem(Control: TWinControl; Index: Integer; Rect: TRect; State: TOwnerDrawState);
begin
  with ListBox1.Canvas do
  begin
    ListBox1.Canvas.FillRect(Rect);
    TextOut(Rect.Left, Rect.Top, ListBox1.Items[Index]);
  end;
  ListBox1.Height := ListBox1.ItemHeight*ListBox1.Items.Count;
end;