偏好设置字幕

在大多数情况下，添加偏好设置摘要相对比较简单，因为这只涉及使用适当的字符串资源将 android:summary 属性添加到相应的偏好设置中。不过，如果字幕应动态更新，那么可能有必要使用自定义偏好设置控制器。

静态字幕

如需向偏好设置添加静态字幕，请执行以下操作：

1. 将 android:summary 属性添加到偏好设置中。例如，如需向 L0 显示设置偏好设置添加摘要，请在偏好设置属性中添加以下内容：

   android:summary="@string/display_settings_summary"
   

   例如，考虑下面这个完整的偏好设置代码示例：

   <Preference
           android:fragment="com.android.car.settings.display.DisplaySettingsFragment"
           android:icon="@drawable/ic_settings_display"
           android:key="@string/pk_display_settings_entry"
           android:title="@string/display_settings"
           android:summary="@string/display_settings_summary"
           settings:controller="com.android.car.settings.common.DefaultRestrictionsPreferenceController"/>
   

动态字幕

使用 android:summary 属性指定的字幕是静态的，因此无法根据特定条件进行更新。对于动态字幕，您需要修改相应偏好设置的偏好设置控制器。以下示例修改了 L0 位置信息偏好设置，使其具有如下的字幕：指定位置信息服务是处于开启还是关闭状态；如果处于开启状态，还会指明当前有权使用位置信息的应用数量。

1. 定义新字符串：

   <!-- Summary for Location settings when location is off [CHAR LIMIT=NONE] -->
       <string name="location_settings_summary_location_off">Off</string>
       <!-- Summary for Location settings when location is on, explaining how many apps have location permission [CHAR LIMIT=NONE]-->
       <plurals name="location_settings_summary_location_on">
           <item quantity="one">On - <xliff:g id="count">%1$d</xliff:g> app has access to location</item>
           <item quantity="other">On - <xliff:g id="count">%1$d</xliff:g> apps have access to location</item>
       </plurals>
       <!-- Location settings, loading the number of apps which have location permission [CHAR LIMIT=30] -->
       <string name="location_settings_loading_app_permission_stats">Loading\u2026</string>
   

2. 创建一个新的 PreferenceController LocationEntryPreferenceController，以便动态设置和更改位置信息偏好设置摘要文本：

   public class LocationEntryPreferenceController extends PreferenceController<Preference> {
   
       private static final Logger LOG = new Logger(LocationEntryPreferenceController.class);
       private static final IntentFilter INTENT_FILTER_LOCATION_MODE_CHANGED =
               new IntentFilter(LocationManager.MODE_CHANGED_ACTION);
   
       private final Context mContext;
       private final LocationManager mLocationManager;
       /** Total number of apps that have location permissions. */
       private int mNumTotal = -1;
       private int mNumTotalLoading = 0;
       private AtomicInteger mLoadingInProgress = new AtomicInteger(0);
   
       private final BroadcastReceiver mReceiver = new BroadcastReceiver() {
           @Override
           public void onReceive(Context context, Intent intent) {
               refreshUi();
           }
       };
   
       public LocationEntryPreferenceController(Context context, String preferenceKey,
               FragmentController fragmentController, CarUxRestrictions uxRestrictions) {
           super(context, preferenceKey, fragmentController, uxRestrictions);
           mContext = context;
           mLocationManager = (LocationManager) getContext().getSystemService(
                   Service.LOCATION_SERVICE);
       }
   
       @Override
       protected Class<Preference> getPreferenceType() {
           return Preference.class;
       }
   
       @Override
       protected void onStartInternal() {
           getContext().registerReceiver(mReceiver, INTENT_FILTER_LOCATION_MODE_CHANGED);
       }
   
       @Override
       protected void onStopInternal() {
           getContext().unregisterReceiver(mReceiver);
       }
   
       @Override
       protected void updateState(Preference preference) {
           super.updateState(preference);
           updateSummary(preference);
           if (!mLocationManager.isLocationEnabled() || mLoadingInProgress.get() != 0) {
               return;
           }
           mNumTotalLoading = 0;
           // Retrieve a list of users inside the current user profile group.
           List<UserHandle> users = mContext.getSystemService(
                   UserManager.class).getUserProfiles();
           mLoadingInProgress.set(users.size());
           for (UserHandle user : users) {
               Context userContext = createPackageContextAsUser(mContext, user.getIdentifier());
               if (userContext == null) {
                   if (mLoadingInProgress.decrementAndGet() == 0) {
                       setLocationAppCount(preference, mNumTotalLoading);
                   }
                   continue;
               }
               PermissionControllerManager permController =
                       userContext.getSystemService(PermissionControllerManager.class);
               permController.countPermissionApps(
                       Arrays.asList(ACCESS_FINE_LOCATION, ACCESS_COARSE_LOCATION),
                       PermissionControllerManager.COUNT_ONLY_WHEN_GRANTED,
                       (numApps) -> {
                           mNumTotalLoading += numApps;
                           if (mLoadingInProgress.decrementAndGet() == 0) {
                               setLocationAppCount(preference, mNumTotalLoading);
                           }
                       }, null);
           }
       }
   
       @VisibleForTesting
       void setLocationAppCount(Preference preference, int numApps) {
           mNumTotal = numApps;
           updateSummary(preference);
       }
   
       private void updateSummary(Preference preference) {
           String summary = "";
           if (mLocationManager.isLocationEnabled()) {
               if (mNumTotal == -1) {
                   summary = mContext.getString(R.string.location_settings_loading_app_permission_stats);
               } else {
                   summary = mContext.getResources().getQuantityString(
                           R.plurals.location_settings_summary_location_on,
                           mNumTotal, mNumTotal);
               }
           } else {
               summary = mContext.getString(R.string.location_settings_summary_location_off);
           }
           preference.setSummary(summary);
       }
   
       private Context createPackageContextAsUser(Context context, int userId) {
           try {
               return context.createPackageContextAsUser(
                       context.getPackageName(), 0 /* flags */, UserHandle.of(userId));
           } catch (PackageManager.NameNotFoundException e) {
               LOG.e("Failed to create user context", e);
           }
           return null;
       }
   }
   

   对于此示例控制器：

   • 如果停用了位置信息服务，摘要文本将设置为 location_settings_summary_location_off 字符串。
   • 如果启用了位置信息服务，系统会添加具有位置信息权限的应用数量。在加载过程中，系统会显示 location_settings_loading_app_permission_stats 字符串。数据加载完毕后，控制器会将摘要设置为 location_settings_summary_location_on 字符串，并指明拥有访问权限的应用数量。
   • 偏好设置控制器在启动后会注册接收器，并在位置信息服务状态更改时刷新偏好设置状态。
3. 修改 fragment XML 文件，将新控制器附加到相关偏好设置：

   <Preference
           android:fragment="com.android.car.settings.location.LocationSettingsFragment"
           android:icon="@drawable/ic_settings_location"
           android:key="@string/pk_location_settings_entry"
           android:title="@string/location_settings_title"
           settings:controller="com.android.car.settings.location.LocationEntryPreferenceController"/>