program Project3;

{$APPTYPE CONSOLE}

{$R *.res}

uses
  System.SysUtils;

var
  FS: TFormatSettings;

const
  DF = 'yyyymmdd';

begin
  try
   WriteLn(FormatDateTime(DF,Now));

   FS := TFormatSettings.Create;
   FS.ShortDateFormat := DF;
   WriteLn(StrToDate('20121219',FS));

   ReadLn;
  except
    on E: Exception do
      Writeln(E.ClassName,': ',E.Message);
  end;
end.

为什么会抛出异常,说“20121219”不是有效的日期？ TFormatSettings应该怎么做？