Cache inflated view to avoid inflation of layouts in preferences

Cache inflated view to avoid inflation of layouts in preferences
If layout id is specified for a Preference object, convertView is set to null
in its adapter which results in inflation of Preference view in getView each time the Preference object is laid out on the screen.
Just use an instance variable to cache the inflated view nulling it whenever the layout changes and use it in initing the convertView in getView.