如何知道鼠标按键是否一直按着

procedure TForm1.Timer1Timer(Sender: TObject); var keystate:TKeyboardState;
begin
caption:='';
GetKeyboardState(keystate);
if keystate[vk_lbutton] and $80 <>0 then
caption:='lbutton down';
if keystate[vk_rbutton] and $80 <>0 then
caption:='Rbutton down';
end;