Unable to get correct activePage when processing pagecontainerhide event

Unable to get correct activePage when processing pagecontainerhide event

Demo is   here, as you can see, there are two pages, i want to do something when p1 hides or before p1 hides, i tried to get the activePage, but it seems whatever the event is, the activePage always is next page, for example: p1 -> p2, i got p2.

How can i get the page which is hided?