title: Android - do something in activity when preferences change
body: <p>I have two classes, <code>CustomerPreferences</code> which <code>extends PreferenceActivity implements OnSharedPreferenceChangeListener</code> and <code>CustomerActivity</code> which <code>extends Activity</code>.  In <code>CustomerActivity</code>, I calculate some values.  In <code>CustomerPreferences</code> there's a particular <code>ListPreference</code> I want to monitor.  When the user enters <code>CustomerPreferences</code>--which is done via a menu option on <code>CustomerActivity</code>--and changes that <code>ListPreference</code>, then hits the back button and returns to <code>CustomerActivity</code>, I want to recalculate my values based on the new preference setting.  If the user goes into <code>CustomerPreferences</code> but doesn't change the value of the <code>ListPreference</code>, I don't want to recalculate anything upon return to <code>CustomerActivity</code>.</p>
  
  <p>How can I do this?</p>
  
  <p>I figure I'll need to do something in <code>CustomerPreferences.onSharedPreferenceChanged</code> as well as maybe <code>CustomerPreferences.onBackPressed</code>, then probably handle something in <code>CustomerActivity</code>.</p>