TTimer = class(TComponent)
  private
    //间隔时间
    FInterval: Cardinal;
    //接收消息的句柄
    FWindowHandle: HWND;
    //用户事件
    FOnTimer: TNotifyEvent;
    FEnabled: Boolean;
    //当属性设置后,更新计时器
    //kill掉已有的,然后创建新的
    procedure UpdateTimer;
    //Setter
    procedure SetEnabled(Value: Boolean);
    procedure SetInterval(Value: Cardinal);
    procedure SetOnTimer(Value: TNotifyEvent);
    //窗体过程
    procedure WndProc(var Msg: TMessage);
  protected
    procedure Timer; dynamic;
{$IF DEFINED(CLR)}
  strict protected
    procedure Finalize; override;
{$IFEND}
  public
    constructor Create(AOwner: TComponent); override;
    destructor Destroy; override;
  published
    property Enabled: Boolean read FEnabled write SetEnabled default True;
    property Interval: Cardinal read FInterval write SetInterval default 1000;
    property OnTimer: TNotifyEvent read FOnTimer write SetOnTimer;
  end;

procedure TTimer.UpdateTimer;
begin
  if FWindowHandle <> 0 then
    KillTimer(FWindowHandle, 1);

  if (FInterval <> 0) and FEnabled and Assigned(FOnTimer) then
  begin
    if FWindowHandle = 0 then    //分配句柄处理消息
      FWindowHandle := AllocateHWnd(WndProc);
    if SetTimer(FWindowHandle, 1, FInterval, nil) = 0 then
      raise EOutOfResources.Create(SNoTimers);
  end
  else
  if FWindowHandle <> 0 then
  begin
    DeallocateHWnd(FWindowHandle);  //取消句柄处理消息
    FWindowHandle := 0;
  end;
end;

procedure TTimer.WndProc(var Msg: TMessage);
begin
  with Msg do
    if Msg = WM_TIMER then
      try
        Timer;
      except
        Application.HandleException(Self);
      end
    else//其他消息,采用默认的windows处理方式
      Result := DefWindowProc(FWindowHandle, Msg, wParam, lParam);
end;

procedure TTimer.Timer;
begin
  if Assigned(FOnTimer) then FOnTimer(Self);
end;