Event when Component becomes visible?

Is there any event which fires when a Component becomes visible?

I’d like this to do things like, e.g., change the toolbar. Something like the following:

$$(“productView”.attachEvent(“myDesiredOnShowEvent”, function(…) {
$(“toolBar”).showBatch(…)
#do anything else needed when component becomes visible
});

oops. meant to post this in the Touch forum.