How to know if a Fragment is Visible?

I'm using the support library v4 and my questions are, How to know if a Fragment is Visible? and How can I change the propierties of the Layout inflated in the Fragment? Thanks in advance.

---Edit---

I'm using fragments like in the android developers tutorial with a FragmentActivity

You should be able to do the following:

MyFragmentClass test = (MyFragmentClass) getSupportFragmentManager().findFragmentByTag("testID");
if (test != null && test.isVisible()) {
     //DO STUFF
}
else {
    //Whatever
}

Both isVisible() and isAdded() return true as soon as the Fragment is created, and not even actually visible. The only solution that actually works is:

if (isAdded() && isVisible() && getUserVisibleHint()) {
    // ... do your thing
}

This does the job. Period.

NOTICE: getUserVisibleHint() is now deprecated. be careful.