title: Can't get preference set with PreferenceActivity
body: <p>I have this main activity:</p>
  
  <pre><code>public class Home extends Activity {
      @Override
      public void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.home);
          initializeStyle();
      }
      private void initializeStyle() {
          SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this);
          String foobar = prefs.getString("foobar", "hi");
          Log.i("MyActivity", foobar);
      }
  // ...
  }
  </code></pre>
  
  <p>And this PreferenceActivity:</p>
  
  <pre><code>public class Preferences extends PreferenceActivity {
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          addPreferencesFromResource(R.xml.preferences);
      }
  }
  </code></pre>
  
  <p>With this XML:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;PreferenceScreen
    xmlns:android="http://schemas.android.com/apk/res/android"&gt;
  &lt;PreferenceCategory 
          android:key="preferences_font"
          android:title="@string/preferences_font"&gt;
      &lt;EditTextPreference
              android:title="@string/preferences_font_size"
              android:key="foobar"
              android:defaultValue="12"&gt;
      &lt;/EditTextPreference&gt;
  &lt;/PreferenceCategory&gt;
  &lt;/PreferenceScreen&gt;
  </code></pre>
  
  <p>Log.i prints "hi", so it means this preference doesn't exist or I named it badly.</p>
  
  <p>Any idea about what I've done wrong?</p>
  
  <p>Regards,</p>