Make BottomNavBar accessible (#15211)

packages/flutter/lib/src/material/bottom_navigation_bar.dart

@@ -13,6 +13,7 @@ import 'colors.dart';
 import 'constants.dart';
 import 'ink_well.dart';
 import 'material.dart';
+import 'material_localizations.dart';
 import 'theme.dart';
 import 'typography.dart';
 
@@ -129,9 +130,11 @@ class _BottomNavigationTile extends StatelessWidget {
     this.iconSize, {
     this.onTap,
     this.colorTween,
-    this.flex
+    this.flex,
+    this.selected: false,
+    this.indexLabel,
     }
-  );
+  ): assert(selected != null);
 
   final BottomNavigationBarType type;
   final BottomNavigationBarItem item;
@@ -140,6 +143,8 @@ class _BottomNavigationTile extends StatelessWidget {
   final VoidCallback onTap;
   final ColorTween colorTween;
   final double flex;
+  final bool selected;
+  final String indexLabel;
 
   Widget _buildIcon() {
     double tweenStart;
@@ -255,7 +260,12 @@ class _BottomNavigationTile extends StatelessWidget {
     }
     return new Expanded(
       flex: size,
-      child: new InkResponse(
+      child: new Semantics(
+        container: true,
+        selected: selected,
+        child: new Stack(
+          children: <Widget>[
+            new InkResponse(
               onTap: onTap,
               child: new Column(
                 crossAxisAlignment: CrossAxisAlignment.center,
@@ -267,6 +277,12 @@ class _BottomNavigationTile extends StatelessWidget {
                 ],
               ),
             ),
+            new Semantics(
+              label: indexLabel,
+            )
+          ],
+        ),
+      ),
     );
   }
 }
@@ -368,6 +384,8 @@ class _BottomNavigationBarState extends State<BottomNavigationBar> with TickerPr
   }
 
   List<Widget> _createTiles() {
+    final MaterialLocalizations localizations = MaterialLocalizations.of(context);
+    assert(localizations != null);
     final List<Widget> children = <Widget>[];
     switch (widget.type) {
       case BottomNavigationBarType.fixed:
@@ -398,6 +416,8 @@ class _BottomNavigationBarState extends State<BottomNavigationBar> with TickerPr
                   widget.onTap(i);
               },
               colorTween: colorTween,
+              selected: i == widget.currentIndex,
+              indexLabel: localizations.tabLabel(tabIndex: i + 1, tabCount: widget.items.length),
             ),
           );
         }
@@ -415,7 +435,9 @@ class _BottomNavigationBarState extends State<BottomNavigationBar> with TickerPr
                   widget.onTap(i);
               },
               flex: _evaluateFlex(_animations[i]),
-            ),
+              selected: i == widget.currentIndex,
+              indexLabel: localizations.tabLabel(tabIndex: i + 1, tabCount: widget.items.length),
+            )
           );
         }
         break;

packages/flutter/test/material/bottom_navigation_bar_test.dart

@@ -2,11 +2,14 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:ui';
+
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 import '../rendering/mock_canvas.dart';
+import '../widgets/semantics_tester.dart';
 
 void main() {
   testWidgets('BottomNavigationBar callback test', (WidgetTester tester) async {
@@ -483,11 +486,78 @@ void main() {
     await tester.pump(const Duration(milliseconds: 20));
     expect(box, paints..circle(x: 600.0)..circle(x: 200.0)..circle(x: 600.0));
   });
+
+  testWidgets('BottomNavigationBar semantics', (WidgetTester tester) async {
+    final SemanticsTester semantics = new SemanticsTester(tester);
+
+    await tester.pumpWidget(
+      boilerplate(
+        textDirection: TextDirection.ltr,
+        bottomNavigationBar: new BottomNavigationBar(
+          items: const <BottomNavigationBarItem>[
+            const BottomNavigationBarItem(
+              icon: const Icon(Icons.ac_unit),
+              title: const Text('AC'),
+            ),
+            const BottomNavigationBarItem(
+              icon: const Icon(Icons.access_alarm),
+              title: const Text('Alarm'),
+            ),
+            const BottomNavigationBarItem(
+              icon: const Icon(Icons.hot_tub),
+              title: const Text('Hot Tub'),
+            ),
+          ],
+        ),
+      ),
+    );
+
+    // TODO(goderbauer): traversal order is incorrect, https://github.com/flutter/flutter/issues/14375
+    final TestSemantics expected = new TestSemantics.root(
+      children: <TestSemantics>[
+        new TestSemantics(
+          id: 1,
+          flags: <SemanticsFlag>[SemanticsFlag.isSelected],
+          actions: <SemanticsAction>[SemanticsAction.tap],
+          label: 'AC\nTab 1 of 3',
+          textDirection: TextDirection.ltr,
+          nextNodeId: -1,
+          previousNodeId: 3, // Should be 2
+        ),
+        new TestSemantics(
+          id: 2,
+          actions: <SemanticsAction>[SemanticsAction.tap],
+          label: 'Alarm\nTab 2 of 3',
+          textDirection: TextDirection.ltr,
+          nextNodeId: 3,
+          previousNodeId: -1, // Should be 1
+        ),
+        new TestSemantics(
+          id: 3,
+          actions: <SemanticsAction>[SemanticsAction.tap],
+          label: 'Hot Tub\nTab 3 of 3',
+          textDirection: TextDirection.ltr,
+          nextNodeId: 1, // Should be -1
+          previousNodeId: 2,
+        ),
+      ],
+    );
+    expect(semantics, hasSemantics(expected, ignoreTransform: true, ignoreRect: true));
+
+    semantics.dispose();
+  });
+
 }
 
 Widget boilerplate({ Widget bottomNavigationBar, @required TextDirection textDirection }) {
   assert(textDirection != null);
-  return new Directionality(
+  return new Localizations(
+    locale: const Locale('en', 'US'),
+    delegates: <LocalizationsDelegate<dynamic>>[
+      DefaultMaterialLocalizations.delegate,
+      DefaultWidgetsLocalizations.delegate,
+    ],
+    child: new Directionality(
       textDirection: textDirection,
       child: new MediaQuery(
         data: const MediaQueryData(),
@@ -497,5 +567,6 @@ Widget boilerplate({ Widget bottomNavigationBar, @required TextDirection textDir
           ),
         ),
       ),
+    ),
   );
 }