请问这段代码怎么分析，谢谢  if OPD.Execute then
      listbox1.Items.AddObject(ExtractFileName(OPD.Files.Text),OPD.Files)  ;
  end;

procedure Tmainform.CreateButtonClick(Sender: TObject);
var
  i: Integer;
  InFileName, OutFileName: string;
  FilePath, FileName: string;
begin
  for i:=0 to listBox1.Items.Count-1 do
  begin
    InFileName:=trim(ListBox1.Items[i]);
    FilePath:=ExtractFilePath(InFileName);
    FileName:=ExtractFileName(InFileName);
    if setform.OutDirEdit.Text<>'' then
      FilePath:=IncludeTrailingBackSlash(setform.OutDirEdit.Text);
    OutFileName:=Concat(FilePath,setform.PrefixEdit.Text,FileName);
    CreateThumbnail(InFileName,OutFileName,setform.WidthUpDown.Position,
     setform.HeightUpDown.Position,setform.Shape1.Brush.Color);
    Application.ProcessMessages;
    StatusBar1.Panels[0].Text:='完成 '+IntToStr(i+1)+' of '+IntToStr(listBox1.Items.count);
  end;
end;