add cupertino localizations (#20756)

add cupertino localizations abstract class and the default cupertino localizations in US English.

packages/flutter/lib/cupertino.dart

@@ -15,6 +15,7 @@ export 'src/cupertino/button.dart';
 export 'src/cupertino/colors.dart';
 export 'src/cupertino/dialog.dart';
 export 'src/cupertino/icons.dart';
+export 'src/cupertino/localizations.dart';
 export 'src/cupertino/nav_bar.dart';
 export 'src/cupertino/page_scaffold.dart';
 export 'src/cupertino/picker.dart';

packages/flutter/lib/src/cupertino/localizations.dart

@@ -0,0 +1,266 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter/widgets.dart';
+
+
+/// Defines the localized resource values used by the Cupertino widgets.
+///
+/// See also:
+///
+///  * [DefaultCupertinoLocalizations], the default, English-only, implementation
+///    of this interface.
+// TODO(xster): Supply non-english strings.
+abstract class CupertinoLocalizations {
+  /// Year that is shown in [CupertinoDatePicker] spinner corresponding to the
+  /// given year index.
+  ///
+  /// Examples: datePickerYear(1) in:
+  ///
+  ///  - US English: 2018
+  ///  - Korean: 2018년
+  String datePickerYear(int yearIndex);
+
+  /// Month that is shown in [CupertinoDatePicker] spinner corresponding to
+  /// the given month index.
+  ///
+  /// Examples: datePickerMonth(1) in:
+  ///
+  ///  - US English: January
+  ///  - Korean: 1월
+  String datePickerMonth(int monthIndex);
+
+  /// Day of month that is shown in [CupertinoDatePicker] spinner corresponding
+  /// to the given day index.
+  ///
+  /// Examples: datePickerDayOfMonth(1) in:
+  ///
+  ///  - US English: 1
+  ///  - Korean: 1일
+  String datePickerDayOfMonth(int dayIndex);
+
+  /// The medium-width date format that is shown in [CupertinoDatePicker]
+  /// spinner. Abbreviates month and days of week.
+  ///
+  /// Examples:
+  ///
+  /// - US English: Wed Sep 27
+  /// - Russian: ср сент. 27
+  String datePickerMediumDate(DateTime date);
+
+  /// Hour that is shown in [CupertinoDatePicker] spinner corresponding
+  /// to the given hour value.
+  ///
+  /// Examples: datePickerHour(1) in:
+  ///
+  ///  - US English: 01
+  ///  - Arabic: ٠١
+  String datePickerHour(int hour);
+
+  /// Minute that is shown in [CupertinoDatePicker] spinner corresponding
+  /// to the given minute value.
+  ///
+  /// Examples: datePickerMinute(1) in:
+  ///
+  ///  - US English: 01
+  ///  - Arabic: ٠١
+  String datePickerMinute(int minute);
+
+  /// The order of the date elements that will be shown in [CupertinoDatePicker].
+  /// Can be any permutation of 'DMY' ('D': day, 'M': month, 'Y': year).
+  String get datePickerDateOrder;
+
+  /// The abbreviation for ante meridiem (before noon) shown in the time picker.
+  String get anteMeridiemAbbreviation;
+
+  /// The abbreviation for post meridiem (after noon) shown in the time picker.
+  String get postMeridiemAbbreviation;
+
+  /// Hour that is shown in [CupertinoCountdownTimerPicker] corresponding to
+  /// the given hour value.
+  ///
+  /// Examples: timerPickerHour(1) in:
+  ///
+  ///  - US English: 1
+  ///  - Arabic: ١
+  String timerPickerHour(int hour);
+
+  /// Minute that is shown in [CupertinoCountdownTimerPicker] corresponding to
+  /// the given minute value.
+  ///
+  /// Examples: timerPickerMinute(1) in:
+  ///
+  ///  - US English: 1
+  ///  - Arabic: ١
+  String timerPickerMinute(int minute);
+
+  /// Second that is shown in [CupertinoCountdownTimerPicker] corresponding to
+  /// the given second value.
+  ///
+  /// Examples: timerPickerSecond(1) in:
+  ///
+  ///  - US English: 1
+  ///  - Arabic: ١
+  String timerPickerSecond(int second);
+
+  /// Label that appears next to the hour picker in
+  /// [CupertinoCountdownTimerPicker] when selected hour value is `hour`.
+  /// This function will deal with pluralization based on the `hour` parameter.
+  String timerPickerHourLabel(int hour);
+
+  /// Label that appears next to the minute picker in
+  /// [CupertinoCountdownTimerPicker] when selected minute value is `minute`.
+  /// This function will deal with pluralization based on the `minute` parameter.
+  String timerPickerMinuteLabel(int minute);
+
+  /// Label that appears next to the minute picker in
+  /// [CupertinoCountdownTimerPicker] when selected minute value is `second`.
+  /// This function will deal with pluralization based on the `second` parameter.
+  String timerPickerSecondLabel(int second);
+
+  /// The `CupertinoLocalizations` from the closest [Localizations] instance
+  /// that encloses the given context.
+  ///
+  /// This method is just a convenient shorthand for:
+  /// `Localizations.of<CupertinoLocalizations>(context, CupertinoLocalizations)`.
+  ///
+  /// References to the localized resources defined by this class are typically
+  /// written in terms of this method. For example:
+  ///
+  /// ```dart
+  /// CupertinoLocalizations.of(context).anteMeridiemAbbreviation;
+  /// ```
+  static CupertinoLocalizations of(BuildContext context) {
+    return Localizations.of<CupertinoLocalizations>(context, CupertinoLocalizations);
+  }
+}
+
+class _CupertinoLocalizationsDelegate extends LocalizationsDelegate<CupertinoLocalizations> {
+  const _CupertinoLocalizationsDelegate();
+
+  @override
+  bool isSupported(Locale locale) => locale.languageCode == 'en';
+
+  @override
+  Future<CupertinoLocalizations> load(Locale locale) => DefaultCupertinoLocalizations.load(locale);
+
+  @override
+  bool shouldReload(_CupertinoLocalizationsDelegate old) => false;
+}
+
+/// US English strings for the cupertino widgets.
+class DefaultCupertinoLocalizations implements CupertinoLocalizations {
+  /// Constructs an object that defines the cupertino widgets' localized strings
+  /// for US English (only).
+  ///
+  /// [LocalizationsDelegate] implementations typically call the static [load]
+  /// function, rather than constructing this class directly.
+  const DefaultCupertinoLocalizations();
+
+  static const List<String> _shortWeekdays = <String>[
+    'Mon',
+    'Tue',
+    'Wed',
+    'Thu',
+    'Fri',
+    'Sat',
+    'Sun',
+  ];
+
+  static const List<String> _shortMonths = <String>[
+    'Jan',
+    'Feb',
+    'Mar',
+    'Apr',
+    'May',
+    'Jun',
+    'Jul',
+    'Aug',
+    'Sep',
+    'Oct',
+    'Nov',
+    'Dec',
+  ];
+
+  static const List<String> _months = <String>[
+    'January',
+    'February',
+    'March',
+    'April',
+    'May',
+    'June',
+    'July',
+    'August',
+    'September',
+    'October',
+    'November',
+    'December',
+  ];
+
+  @override
+  String datePickerYear(int yearIndex) => yearIndex.toString();
+
+  @override
+  String datePickerMonth(int monthIndex) => _months[monthIndex - 1];
+
+  @override
+  String datePickerDayOfMonth(int dayIndex) => dayIndex.toString();
+
+  @override
+  String datePickerHour(int hour) => hour.toString().padLeft(2, '0');
+
+  @override
+  String datePickerMinute(int minute) => minute.toString().padLeft(2, '0');
+
+  @override
+  String datePickerMediumDate(DateTime date) {
+    return '${_shortWeekdays[date.weekday - DateTime.monday]} '
+      '${_shortMonths[date.month - DateTime.january]} '
+      '${date.day}';
+  }
+
+  @override
+  String get datePickerDateOrder => 'MDY';
+
+  @override
+  String get anteMeridiemAbbreviation => 'AM';
+
+  @override
+  String get postMeridiemAbbreviation => 'PM';
+
+  @override
+  String timerPickerHour(int hour) => hour.toString();
+
+  @override
+  String timerPickerMinute(int minute) => minute.toString();
+
+  @override
+  String timerPickerSecond(int second) => second.toString();
+
+  @override
+  String timerPickerHourLabel(int hour) => hour == 1 ? 'hour' : 'hours';
+
+  @override
+  String timerPickerMinuteLabel(int minute) => 'min';
+
+  @override
+  String timerPickerSecondLabel(int second) => 'sec';
+
+  /// Creates an object that provides US English resource values for the
+  /// cupertino library widgets.
+  ///
+  /// The [locale] parameter is ignored.
+  ///
+  /// This method is typically used to create a [LocalizationsDelegate].
+  static Future<CupertinoLocalizations> load(Locale locale) {
+    return new SynchronousFuture<CupertinoLocalizations>(const DefaultCupertinoLocalizations());
+  }
+
+  /// A [LocalizationsDelegate] that uses [DefaultCupertinoLocalizations.load]
+  /// to create an instance of this class.
+  static const LocalizationsDelegate<CupertinoLocalizations> delegate = _CupertinoLocalizationsDelegate();
+}

packages/flutter/test/cupertino/localizations_test.dart

@@ -0,0 +1,30 @@
+// Copyright 2016 The Chromium Authors. 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:flutter/cupertino.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('English translations exist for all CupertinoLocalization properties', (WidgetTester tester) async {
+    const CupertinoLocalizations localizations = DefaultCupertinoLocalizations();
+
+    expect(localizations.datePickerYear(2018), isNotNull);
+    expect(localizations.datePickerMonth(1), isNotNull);
+    expect(localizations.datePickerDayOfMonth(1), isNotNull);
+    expect(localizations.datePickerHour(0), isNotNull);
+    expect(localizations.datePickerMinute(0), isNotNull);
+    expect(localizations.datePickerMediumDate(DateTime.now()), isNotNull);
+    expect(localizations.datePickerDateOrder, isNotNull);
+
+    expect(localizations.anteMeridiemAbbreviation, isNotNull);
+    expect(localizations.postMeridiemAbbreviation, isNotNull);
+
+    expect(localizations.timerPickerHour(0), isNotNull);
+    expect(localizations.timerPickerMinute(0), isNotNull);
+    expect(localizations.timerPickerSecond(0), isNotNull);
+    expect(localizations.timerPickerHourLabel(0), isNotNull);
+    expect(localizations.timerPickerMinuteLabel(0), isNotNull);
+    expect(localizations.timerPickerSecondLabel(0), isNotNull);
+  });
+}