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96 lines
4.7 KiB
ReStructuredText
96 lines
4.7 KiB
ReStructuredText
==================================
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Runtime locale switching in Fennec
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==================================
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`Bug 917480 <https://bugzilla.mozilla.org/show_bug.cgi?id=917480>`_ built on `Bug 936756 <https://bugzilla.mozilla.org/show_bug.cgi?id=936756>`_ to allow users to switch between supported locales at runtime, within Fennec, without altering the system locale.
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This document aims to describe the overall architecture of the solution, along with guidelines for Fennec developers.
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Overview
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========
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There are two places that locales are relevant to an Android application: the Java ``Locale`` object and the Android configuration itself.
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Locale switching involves manipulating these values (to affect future UI), persisting them for future activities, and selectively redisplaying existing UI elements to give the appearance of responsive switching.
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The user's choice of locale is stored in a per-app pref, ``"locale"``. If missing, the system default locale is used. If set, it should be a locale code like ``"es"`` or ``"en-US"``.
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``BrowserLocaleManager`` takes care of updating the active locale when asked to do so. It also manages persistence and retrieval of the locale preference.
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The question, then, is when to do so.
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Locale events
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=============
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One might imagine that we need only set the locale when our Application is instantiated, and when a new locale is set. Alas, that's not the case: whenever there's a configuration change (*e.g.*, screen rotation), when a new activity is started, and at other apparently random times, Android will supply our activities with a configuration that's been reset to the sytem locale.
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For this reason, each starting activity must ask ``BrowserLocaleManager`` to fix its locale.
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Ideally, we also need to perform some amount of work when our configuration changes, when our activity is resumed, and perhaps when a result is returned from another activity, if that activity can change the app locale (as is the case for any activity that calls out to ``GeckoPreferences`` -- see ``BrowserApp#onActivityResult``).
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``GeckoApp`` itself does some additional work, because it has particular performance constraints, and also is the typical root of the preferences activity.
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Here's an example of the work that a typical activity should do::
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// This is cribbed from o.m.g.sync.setup.activities.LocaleAware.
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public static void initializeLocale(Context context) {
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final LocaleManager localeManager = BrowserLocaleManager.getInstance();
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if (Build.VERSION.SDK_INT < Build.VERSION_CODES.GINGERBREAD) {
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localeManager.getAndApplyPersistedLocale(context);
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} else {
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final StrictMode.ThreadPolicy savedPolicy = StrictMode.allowThreadDiskReads();
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StrictMode.allowThreadDiskWrites();
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try {
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localeManager.getAndApplyPersistedLocale(context);
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} finally {
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StrictMode.setThreadPolicy(savedPolicy);
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}
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}
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}
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@Override
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public void onConfigurationChanged(Configuration newConfig) {
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final LocaleManager localeManager = BrowserLocaleManager.getInstance();
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final Locale changed = localeManager.onSystemConfigurationChanged(this, getResources(), newConfig, mLastLocale);
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if (changed != null) {
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// Redisplay to match the locale.
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onLocaleChanged(BrowserLocaleManager.getLanguageTag(changed));
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}
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}
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@Override
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public void onCreate(Bundle icicle) {
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// Note that we don't do this in onResume. We should,
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// but it's an edge case that we feel free to ignore.
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// We also don't have a hook in this example for when
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// the user picks a new locale.
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initializeLocale(this);
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super.onCreate(icicle);
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}
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``GeckoApplication`` itself handles correcting locales when the configuration changes; your activity shouldn't need to do this itself. See ``GeckoApplication``'s and ``GeckoApp``'s ``onConfigurationChanged`` methods.
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System locale changes
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=====================
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Fennec can be in one of two states.
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If the user has not explicitly chosen a Fennec-specific locale, we say
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we are "mirroring" the system locale.
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When we are not mirroring, system locale changes do not impact Fennec
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and are essentially ignored; the user's locale selection is the only
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thing we care about, and we actively correct incoming configuration
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changes to reflect the user's chosen locale.
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By contrast, when we are mirroring, system locale changes cause Fennec
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to reflect the new system locale, as if the user picked the new locale.
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When the system locale changes when we're mirroring, your activity will receive an ``onConfigurationChanged`` call. Simply pass this on to ``BrowserLocaleManager``, and then handle the response appropriately.
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Further reference
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=================
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``GeckoPreferences``, ``GeckoApp``, and ``BrowserApp`` are excellent resources for figuring out what you should do.
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