Where to store Android preference keys?

Question

When I create preference activity I define all preferences in xml file. Every preference has a key defined in this xml. But when I access preference I write:

Answer 1

What about using a helper class to hide the getString() - instantiate the helper once in each activity or service. For example:

class Pref {

    final String smsEnable_pref;
    final String interval_pref;
    final String sendTo_pref;
    final String customTemplate_pref;
    final String webUrl_pref;

    Pref(Resources res) {       
         smsEnable_pref = res.getString(R.string.smsEnable_pref);
         interval_pref = res.getString(R.string.interval_pref);
         sendTo_pref = res.getString(R.string.sendTo_pref);
         customTemplate_pref = res.getString(R.string.customTemplate_pref);
         webUrl_pref = res.getString(R.string.webUrl_pref);
    }
}