偏好字幕

在大多數情況下，添加首選項摘要相對簡單，因為它只涉及使用適當的字符串資源將android:summary屬性添加到相應的首選項中。但是，如果字幕應該動態更新，則可能需要自定義首選項控制器。

靜態字幕

要將靜態字幕添加到首選項：

  1. 將android:summary屬性添加到首選項。例如，要向 L0 顯示設置首選項添加摘要，請在首選項屬性中添加類似以下內容：
    android:summary="@string/display_settings_summary"

    例如，考慮這個完整的偏好代碼示例：

    <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"/>

動態字幕

使用android:summary屬性指定的字幕是靜態的，因此無法根據某些條件進行更新。對於動態字幕，您需要修改首選項的首選項控制器。以下示例將 L0 位置首選項修改為具有指定位置是打開還是關閉的副標題，如果打開，則說明當前有多少應用程序具有位置訪問權限。

  1. 定義新字符串：
    <!-- 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. 創建一個新的 PreferenceController LocationEntryPreferenceController來動態設置和更改位置偏好摘要文本：
    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;
    }
}

    對於此示例控制器：

    • 如果位置被禁用，摘要文本設置為location_settings_summary_location_off字符串。
    • 如果啟用了位置，則會添加具有位置權限的應用程序的數量。在加載時，會顯示location_settings_loading_app_permission_stats字符串。加載數據時，控制器將摘要設置為location_settings_summary_location_on字符串，並指定具有訪問權限的應用程序的數量。
    • 當偏好控制器啟動時，控制器註冊一個接收器並在位置狀態改變時刷新偏好狀態。
  3. 修改片段 XML 文件以將新控制器附加到相關首選項：
    <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"/>