Delphi FMX TListBox slow with large lists

Question

I'm loading 2,000 names into an FMX TListBox and it is taking far too long (like 35 seconds or more).

Here is the test code:

procedure TDocWindow.DEBUGAddLotsOfStringsToList;
var
  theTimeAtStart: Integer;
  J: Integer;

begin
  ListBox1.Clear;

  theTimeAtStart := TThread.GetTickCount;

  for J := 1 to 2200 do
    begin
      ListBox1.Items.Add(j.toString);
    end;

  ShowMessage('There were ' + J.ToString + ' strings added to the list in ' + (TThread.GetTickCount - theTimeAtStart).ToString + ' milliseconds.');
end;

Is there something about TListBox that makes it too slow for a few thousand strings?

Ken White Ken White · Accepted Answer · 2020-07-24T01:02:55

Using BeginUpdate and EndUpdate reduced the runtime on my system from 25 seconds to about 125 ms.

procedure TForm1.Button1Click(Sender: TObject);
var
  theTimeAtStart: Integer;
  J: Integer;
begin
  theTimeAtStart := TThread.GetTickCount;

  ListBox1.Items.BeginUpdate;

  try
    ListBox1.Clear;

    for J := 1 to 2200 do
    begin
      ListBox1.Items.Add(j.ToString());
    end;
  finally
    ListBox1.Items.EndUpdate;
  end;
  ShowMessage('There were ' + J.ToString + ' strings added to the list in ' + (TThread.GetTickCount - theTimeAtStart).ToString + ' milliseconds.');
end;

Delphi FMX TListBox slow with large lists

1 Answers