Call to getLayoutInflater() in places not in activity
You can use this outside activities - all you need is to provide a Context:
LayoutInflater inflater = (LayoutInflater) context.getSystemService( Context.LAYOUT_INFLATER_SERVICE );
Then to retrieve your different widgets, you inflate a layout:
View view = inflater.inflate( R.layout.myNewInflatedLayout, null );
Button myButton = (Button) view.findViewById( R.id.myButton );
EDIT as of July 2014
Davide's answer on how to get the LayoutInflater is actually more correct than mine (which is still valid though).
Or ...
LayoutInflater inflater = LayoutInflater.from(context);