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偏好字幕

大多數情況下，新增偏好設定摘要相對簡單明瞭只要在對應的偏好設定中加入 android:summary 屬性即可傳回適當的字串資源但如果字幕必須能夠動態更新那麼您可能需要自訂偏好設定控制器

靜態字幕

如何為偏好設定新增靜態子標題：

在偏好設定中加入 android:summary 屬性。舉例來說，如要新增摘要到 L0 顯示設定偏好設定中，請在偏好設定屬性：

android:summary="@string/display_settings_summary"

以完整的偏好設定程式碼範例為例：

<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，因此無法顯示並根據特定條件進行更新如要使用動態字幕，請調整偏好設定控制器。以下範例將 L0 位置偏好設定改為副標題，指出位置資訊是否開啟。如已啟用，請說明應用程式數量目前可存取位置資訊。

定義新字串：

<!-- 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>

將新的 PreferenceController、LocationEntryPreferenceController 設為動態設定並變更位置偏好設定摘要文字：

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;
    }
}

這個範例控制器：

如果位置資訊已停用，摘要文字會設為 location_settings_summary_location_off 字串。
如果已啟用定位功能，系統會新增具備位置存取權的應用程式數量。雖然載入中，location_settings_loading_app_permission_stats 字串。載入資料時，控制器會將摘要設為「location_settings_summary_location_on」字串，內含有應用程式數量的應用程式是否設有存取權
偏好設定控制器啟動後，控制器會註冊接收端在位置狀態變更時重新整理偏好設定狀態。

修改片段 XML 檔案，將新控制器附加至相關偏好設定：

<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"/>