NavigationBar - how to disable or hide button as user navigates?

I have added a NavigationBar to my Sencha Touch 2 project, and it automatically adds a 'back' button when I push a view in response to a press of a button in that nav bar.

The problem is, that same button is still visible and the user can click it again, which pushes the same view again. It's just not a good UI experience, and causes some other issues. SO, is there a way either automatically or manually to either hide, disable, or some other best practice to prevent the button from being used if the user is already looking at the view that button is going to push?

NavigationBar - how to disable or hide button as user navigates?