title: PreferenceFragment does not show up in Activity
body: <p>I have followed the guide "settings" from android developers. But when I launch my SettingsActivity all I get is <strong>white screen</strong>. What am I doing wrong?</p>
  
  <p>Here is my SettingActivity.java</p>
  
  <pre><code>public class SettingsActivity extends Activity {
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
  
          getFragmentManager().beginTransaction()
                   .replace(android.R.id.content, new SettingsFragment())
                   .commit();
      }
  }
  </code></pre>
  
  <p>Here is SettingFragment</p>
  
  <pre><code>public class SettingsFragment extends PreferenceFragment {
  
      @Override
      public void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          addPreferencesFromResource(R.xml.preferences);
      }
  }
  </code></pre>
  
  <p>Here is preferences file</p>
  
  <pre><code>&lt;PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android"&gt;
      &lt;EditTextPreference android:title="Your Name"
          android:key="username"
          android:summary="Please provide your username"&gt;&lt;/EditTextPreference&gt;
      &lt;CheckBoxPreference android:title="Application Updates"
          android:defaultValue="false"
          android:summary="This option if selected will allow the application to check for latest versions."
          android:key="applicationUpdates" /&gt;
      &lt;ListPreference     android:title="Download Details"
          android:summary="Select the kind of data that you would like to download"
          android:key="downloadType"
          android:defaultValue="1"
          android:entries="@array/listArray"
          android:entryValues="@array/listValues" /&gt;
  &lt;/PreferenceScreen&gt;
  </code></pre>
  
  <p>And that's how I switch to SettingsActivity</p>
  
  <pre><code>Intent intent = new Intent(MainActivity.this, SettingsActivity.class);
                              startActivity(intent);
  </code></pre>
  
  <p>Is white screen is supposed to happed? I'm expecting a default screen with settings</p>