When you use fragments, you should override the onCreateView method.
Here is an exemple :
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
View v = inflater.inflate(R.layout.YOUR_FRAGMENT_LAYOUT, null);
TextView txtMyTextBox = (TextView)v.findViewById(R.id.my_text_box)
return v;
}