How to close the PopUp In another Page

Question

Hi,

Say I have 2 pages : P1 and P2  and in P2 I have a PopUp1.

in P2 , I open the popup thru a condition which requires to access data thru internet. If I quickly press the Back Button after I launch the PopUp, this PopUp wont close when P2 is opened even I have implement the following in P2

protected override void GoBack(object sender, RoutedEventArgs e)
        {
            base.GoBack(sender, e);

            PopUp1.IsOpen = false;          

        }

How do I close this PopUp1 in P2 ?

Thanks

        }