cakephp $this->params not set in beforeFilter

I needed to do something with $this->params in the AppController::beforeFilter() I get Notice (8): Undefined variable: a but when I set it in beforeFilter() the b variable is set normally. Is this normal behavior? And if it isn't, how do I get the params to be set in beforeFilter()? It would have been better if I could work with the params before any action is called.

function beforeFilter() {
$this-开发者_JS百科>set('a', $this->params);
}

function beforeRender() {
$this->set('b', $this->params);
}

My bad, I had overriden beforeFilter in an controller and forgot to call parent::beforeFilter() at the start. Now it's ok.