Android中`PreferenceScreen`缺少Header/title

<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
    <PreferenceCategory android:title="General Settings">
        <CheckBoxPreference
            android:key="notifications"
            android:title="Notifications"
            android:summary="Enable or disable notifications" />
    </PreferenceCategory>
</PreferenceScreen>

PreferenceScreen preferenceScreen = getPreferenceScreen();
PreferenceCategory generalSettings = new PreferenceCategory(this);
generalSettings.setTitle("General Settings");
preferenceScreen.addPreference(generalSettings);

CheckBoxPreference notifications = new CheckBoxPreference(this);
notifications.setKey("notifications");
notifications.setTitle("Notifications");
notifications.setSummary("Enable or disable notifications");
generalSettings.addPreference(notifications);

<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
    <!-- Customize your theme here. -->
</style>

<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
    <!-- Your preferences here -->
</PreferenceScreen>

public class SettingsActivity extends PreferenceActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        addPreferencesFromResource(R.xml.preferences);
    }
}

public class SettingsFragment extends PreferenceFragmentCompat {
    @Override
    public void onCreatePreferences(Bundle savedInstanceState, String rootKey) {
        setPreferencesFromResource(R.xml.preferences, rootKey);
    }
}