How to dispose vspackage object when package Tab closed?

Hello, 

I am developing a vspackage to connect to our custom database. When initially load the package, my MainWindow.xaml is initializing. But, when I close & re-open the package (only pakcage tab, not visual studio), My mainwindow.xaml is not initializing. Its retaining the objects.

I want to dispose everything when package tabpage window closed not when restart visual studio. How can i do this? I tried to override 'OnClose()' method in myToolWindow.cs, but no luck. 

Any help would greatly appreciated and saves alot of time. Thanks :)