Попробуйте это
View v = inflater.inflate(R.layout.messages_fragment, null);
ListView messagesListView = (ListView) v
.findViewById(R.id.messages_list);
return v;
или в getView return
return inflater.inflate(R.layout.messages_fragment, null);
Затем
public void onActivityCreated(Bundle savedInstanceState) {
View v= getView();
ListView messagesListView = (ListView) v.findViewById(R.id.messages_list);
... // rest of the code
}