How to animate a manager to expand when it receives focus in blackberry?

In my app, I am using a manager whose height is controlled by using its sublayout() method. Now when this manager(or any of the fields inside it) receives focus, I am able to increase the manager's height all at once, but i wan开发者_Go百科t to make it animate and gradually increase its height. How shall i achieve this?

I am developing for OS 5.0 and above.

Use the timer in the paint method and expand its height every X milliseconds...