在一个旧帖里发现TTimer的小问题，请教一下

unit PreciseTimerUnit;



interface



uses

  Windows,MMSystem,UnitManagedObject;



type

  TTimerEvent=procedure (Sender:TObject) of Object;



  TPreciseTimer=class(TManagedObject)

    strict private

       FPurifierTimer:UINT;

       FOnTimerEvent:TTimerEvent;

       FInterval: UINT;

       FResolution: UINT;

    private

      procedure RaiseTimerEvent;

    public

      property OnTimer:TTimerEvent read FOnTimerEvent write FOnTimerEvent;

      property Interval: UINT read FInterval;

    public

      Constructor Create;overload;

      Constructor Create(AInterval: UINT);overload;

      Destructor Destroy;override;

  end;

const

  TIME_KILL_SYNCHRONOUS:UINT=$0100;

var

  WinVersion:DWORD;

implementation



function ByteSwap(value:DWORD):DWORD; assembler;

asm

  BSWAP eax

end;



procedure TPreciseTimer.RaiseTimerEvent;

begin

  if Assigned(FOnTimerEvent) then

    FOnTimerEvent(Self);

end;



procedure PurifierTimerProc(uTimerID, uMessage: UINT;

    dwUser, dw1, dw2: DWORD) stdcall;

var

  pTimer: TPreciseTimer;

begin



  pTimer := TPreciseTimer(dwUser);

  if pTimer.Attach <> pTimer then

    Exit;

  try

    pTimer.RaiseTimerEvent;

  finally

    pTimer.Free;

  end;

end;



constructor TPreciseTimer.Create;

begin

	Create(1000);

end;



constructor TPreciseTimer.Create(AInterval: UINT);

var

  fuEvent:UINT;

  tc: TIMECAPS;

begin

  Inherited Create;

  FInterval := AInterval;

  FOnTimerEvent := Nil;

  if timeGetDevCaps(@tc, SizeOf(TIMECAPS)) <> TIMERR_NOERROR then Exit;

  FResolution := tc.wPeriodMin;

  if timeBeginPeriod(FResolution) <> TIMERR_NOERROR then Exit;;



  fuEvent:=TIME_PERIODIC;

   if(HiWord(byteswap( WinVersion))>=$501) then//WinXP or Later

      fuEvent:=fuEvent or TIME_KILL_SYNCHRONOUS;



   FPurifierTimer:=timeSetEvent(Interval,

                               0,

                               PurifierTimerProc,

                               DWORD_PTR(self),

                               fuEvent);

   if(0=FPurifierTimer) then

    timeEndPeriod(FResolution);

end;



destructor TPreciseTimer.Destroy;

begin

  if(0<>FPurifierTimer) then

    begin

      timeKillEvent(FPurifierTimer);

      timeEndPeriod(FResolution);

      FPurifierTimer:=0;

      Sleep(15);

    end;

end;



initialization

  WinVersion:=GetVersion;

finalization



end.