feat(#50): Support UI update when updating locale using NStack SDK instance (#54)

* feat(#50): Introduce onLocaleChanged stream

* refactor(#50): Make methods return futures

* feat(#50): Subscribe to the stream in the NStackWidget

* chore(#50): Update example

Author: nivisi

example/lib/main.dart

@@ -41,7 +41,7 @@ class MainScreen extends StatelessWidget {
                 ? const Locale('de-DE')
                 : const Locale('en-EN');
 
-            NStackScope.of(context).changeLanguage(locale);
+            NStack.localization.changeLocalization(locale);
           },
           child: Text(
             'Selected locale: ${activeLanguage.name}',

example/lib/nstack.dart

@@ -21,6 +21,8 @@
  * `context.localization.yourSection.yourKey`.
  */
 
+import 'dart:async';
+
 import 'package:flutter/foundation.dart';
 import 'package:flutter/widgets.dart';
 import 'package:nstack/models/app_open_platform.dart';
@@ -181,19 +183,36 @@ class NStackState extends State<NStackWidget> {
 
   late Future<bool> _nstackInitFuture;
 
+  late final StreamSubscription _localeChangedSubscription;
+
   @override
   void initState() {
     super.initState();
 
     _nstackInitFuture = _nstack.init();
+
+    _localeChangedSubscription =
+        NStack.localization.onLocaleChanged.listen(_onLocaleChanged);
+  }
+
+  void _onLocaleChanged(Locale locale) {
+    setState(() {});
   }
 
+  @Deprecated('Use `NStack.localization.changeLocalization` instead')
   Future<void> changeLanguage(Locale locale) {
     return _nstack.localization
         .changeLocalization(locale)
         .whenComplete(() => setState(() {}));
   }
 
+  @override
+  void dispose() {
+    _localeChangedSubscription.cancel();
+
+    super.dispose();
+  }
+
   @override
   Widget build(BuildContext context) {
     if (!_initializedNStack) {

lib/sdk/localization/nstack_localization.dart

@@ -1,3 +1,4 @@
+import 'dart:async';
 import 'dart:convert';
 
 import 'package:flutter/widgets.dart';
@@ -15,6 +16,8 @@ class NStackLocalization<TLocalization> {
   static const _prefsKeyLastUpdated = "nstack_last_updated";
   static const _prefsSelectedLocale = "nstack_selected_locale";
 
+  final _onLocaleChanged = StreamController<Locale>.broadcast();
+
   final NStackConfig config;
   final TLocalization translations;
   final NStackRepository _repository;
@@ -31,6 +34,8 @@ class NStackLocalization<TLocalization> {
 
   String get checksum => LocalizationRepository().checksum;
 
+  Stream<Locale> get onLocaleChanged => _onLocaleChanged.stream;
+
   Locale? clientLocale;
 
   NStackLocalization({
@@ -53,6 +58,19 @@ class NStackLocalization<TLocalization> {
     );
   }
 
+  Future<void> _updateLocaleAndNotify({
+    required Map<String, dynamic> translationData,
+    required String languageLocale,
+    required Locale locale,
+  }) async {
+    await LocalizationRepository().updateLocalization(
+      translationData,
+      languageLocale,
+    );
+
+    _onLocaleChanged.add(locale);
+  }
+
   /// Change the localization in the internal map
   /// 1. Find the best match in the language list that the project was built with
   /// 2. Look if we have a cached localization in preferences and use that
@@ -76,9 +94,10 @@ class NStackLocalization<TLocalization> {
 
         final languageResponse = LocalizationData.fromJson(cachedResponse);
 
-        LocalizationRepository().updateLocalization(
-          languageResponse.data!,
-          localLanguage.language!.locale!,
+        await _updateLocaleAndNotify(
+          translationData: languageResponse.data!,
+          languageLocale: localLanguage.language!.locale!,
+          locale: locale,
         );
 
         _log("Switched cached localization...");
@@ -94,9 +113,10 @@ class NStackLocalization<TLocalization> {
             jsonDecode(localizationResponse),
           );
 
-          LocalizationRepository().updateLocalization(
-            translationJson.data!,
-            localLanguage.language!.locale!,
+          await _updateLocaleAndNotify(
+            translationData: translationJson.data!,
+            languageLocale: localLanguage.language!.locale!,
+            locale: locale,
           );
 
           _log("Switched API localization...");

lib/src/nstack_builder.dart

@@ -115,6 +115,8 @@ class NstackBuilder implements Builder {
  * `context.localization.yourSection.yourKey`.
  */
 
+import 'dart:async';
+
 import 'package:flutter/foundation.dart';
 import 'package:flutter/widgets.dart';
 import 'package:nstack/models/app_open_platform.dart';
@@ -328,17 +330,33 @@ class NStackState extends State<NStackWidget> {
 
   late Future<bool> _nstackInitFuture;
 
+  late final StreamSubscription _localeChangedSubscription;
+
   @override
   void initState() {
     super.initState();
     
 		_nstackInitFuture = _nstack.init();
+
+    _localeChangedSubscription = NStack.localization.onLocaleChanged.listen(_onLocaleChanged);
+  }
+
+  void _onLocaleChanged(Locale locale) {
+    setState(() {});
   }
 
+  @Deprecated('Use `NStack.localization.changeLocalization` instead')
 	Future<void> changeLanguage(Locale locale) {
 		return _nstack.localization.changeLocalization(locale).whenComplete(() => setState(() {}));
 	}
 
+  @override
+  void dispose() {
+    _localeChangedSubscription.cancel();
+
+    super.dispose();
+  }
+
   @override
   Widget build(BuildContext context) {
     if (!_initializedNStack) {

lib/src/repository.dart

@@ -59,7 +59,7 @@ class LocalizationRepository {
     _setupInternalMap();
   }
 
-  void updateLocalization(
+  Future<void> updateLocalization(
     Map<String, dynamic> localizationJson,
     String bestFitLocale,
   ) {
@@ -68,7 +68,7 @@ class LocalizationRepository {
       orElse: () => this._pickedLanguage,
     );
     _sectionsMap = localizationJson;
-    _persistInternalMap();
+    return _persistInternalMap();
   }
 
   overridePickedLanguage(String locale) {
@@ -95,7 +95,7 @@ class LocalizationRepository {
     }
   }
 
-  _persistInternalMap() async {
+  Future<void> _persistInternalMap() async {
     try {
       WidgetsFlutterBinding.ensureInitialized();
       final prefs = await SharedPreferences.getInstance();