Adds a sample for polymer internationalization/localization

samples/polymer_intl/web/localized.dart

Index: samples/polymer_intl/web/localized.dart
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+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:polymer/polymer.dart';
+import 'package:intl/intl.dart';
+import 'messages_all.dart';
+
+/// This is an example polymer component that displays a message in one of
+/// a couple of different locales, based on the user's drop-down list
+/// selection.
+@CustomTag('localized-example')
+class LocalizedExampleElement extends PolymerElement {
+
+  // Polymer likes to use observable variables and doesn't really like
+  // observing getters, requiring us to do explicit notification when the
+  // values that the getter depends on change. So we will save the result
+  // of the message function in an observable variable. That will get
+  // a bit trickier if we have messages that have parameters.
+  @observable String selectedLocale;
+  @observable String helloWorld;
+
+  // It would be simpler to set [helloWorld] in an initializer, but we can't
+  // put a method call in an initializer, so do it in the constructor.
+  LocalizedExampleElement.created() : super.created() {
+    updateLocale(Intl.defaultLocale);
+  }
+
+  // Polymer should call this method automatically if the value of
+  // [selectedLocale] changes.
+  void selectedLocaleChanged() {
+    // We didn't provide en_US translations. We expect it to use the default
+    // text in the messages for en_US. But then we have to not try and
+    // initialize messages for the en_US locale. dartbug.com/15444
+    if (selectedLocale == 'en_US') {
+      updateLocale('en_US');
+      return;
+    }
+    // For the normal case we initialize the messages, wait for initialization
+    // to complete, then update all (all 1 of) our messages.
+    initializeMessages(selectedLocale).then(
+        (succeeded) => updateLocale(selectedLocale));
+  }
+
+  // When the user chooses a new locale, set the default locale for the
+  // whole program to that and update our messages. In a large program this
+  // could get to be a large method. Also, other components might want to
+  // observe the default locale and update accordingly.
+  void updateLocale(localeName) {
+    Intl.defaultLocale = selectedLocale;
+    helloWorld = helloFromDart();
+  }
+
+  // This is our message, a function that would take parameters if we have any
+  // and then gives us back the appropriate translated message.
+  // Of course, in order to make this happen we need to extract the messages
+  // from our program. We don't have an integration with a real translation
+  // system, but you can produce some custom JSON by running (assuming you have
+  // the full Intl package available somewhere, like in a built SDK).
+  //      dart --package-root=<some-path-to-packages>
+  //          <path-to-intl>/intl/test/message_extraction/extract_to_json.dart
+  //          localized.dart
+  // That will produce intl_messages.json. We can then use whatever process
+  // we want to produce translation_fr.json and translation_pt.json. I used
+  // hand-editing, but that doesn't scale. Then
+  //      dart --package-root=<some-path-to-packages>
+  //          <path-to-intl>/intl/test/message_extraction/generate_from_json.dart
+  //          localized.dart translation_fr.json translation_pt.json
+  // will produce messages_all.dart, messages_fr.dart and messages_pt.dart.
+  // We import messages_all.dart, and we're done.
+  helloFromDart() => Intl.message("Hello World from Dart!", name: 'helloWorld',
+      desc: "This is just a simple Hello World message that doesn't"
+        "take any parameters.",
+      args: [], // This would be required if we had any arguments.
+      examples: {"We could put examples of parameter values here for the "
+        "translators if we had any parameters" : 0});
+}