How to force a TListBox to set a horizontol scrollbar if an entry is being cropped

Problem/Question/Abstract:

I have a listbox on a form which contains a list of stuff of varying widths. In some situations, they all fit in the box, in some cases the entries are too long to fit and their right end gets cropped. Is there some way to force the listbox to set a horizontol scrollbar if and only if an entry is being cropped? I can brute force set the ScrollWidth property to 1000, but this puts a scrollbar in place all the time. I only want a scrollbar if it's necessary.

Answer:

{ ... }
listbox.Scrollwidth := CalcMaxWidthOfStrings(listbox.Items, listbox.font);
{ ... }

function CalcMaxWidthOfStrings(aList: TStrings; aFont: TFont): Integer;
var
  max, n, i: Integer;
  canvas: TCanvas;
begin
  Assert(Assigned(aList));
  Assert(Assigned(aFont));
  canvas := TCanvas.Create;
  try
    canvas.Handle := CreateDC('DISPLAY', nil, nil, nil);
    try
      Canvas.Font := aFont;
      max := 0;
      for i := 0 to aList.Count - 1 do
      begin
        n := Canvas.TextWidth(aList[i]);
        if n > max then
          max := n;
      end;
      Result := max;
    finally
      DeleteDC(canvas.Handle);
      canvas.Handle := 0;
    end;
  finally
    canvas.free;
  end;
end;