There is a strange result with
Code:
this.getViewport()
it returns a reference to Ext.MessageBox ?!

The problem is that the reference is not available, but the viewport is the heart of the application.
I was not able for now to add/remove items in the viewport, even when i use itemId and ComponentQuery, for example
Code:
region: 'center',
itemId: 'CenterView',
items: [{
   //...
}]
i can get a reference by
Code:
var centerView = Ext.ComponentQuery.query('#CenterView');
but centerView.removeAll() throws an error.