First pass at keyboard navigation for the Material Date Picker (#59279)

packages/flutter/lib/src/material/pickers/date_picker_header.dart

@@ -8,6 +8,7 @@ import 'package:flutter/widgets.dart';
 
 import '../color_scheme.dart';
 import '../icon_button.dart';
+import '../material.dart';
 import '../text_theme.dart';
 import '../theme.dart';
 
@@ -127,12 +128,11 @@ class DatePickerHeader extends StatelessWidget {
 
     switch (orientation) {
       case Orientation.portrait:
-         return Column(
-          crossAxisAlignment: CrossAxisAlignment.start,
-          children: <Widget>[
-            Container(
+         return SizedBox(
            height: _datePickerHeaderPortraitHeight,
+           child: Material(
              color: primarySurfaceColor,
+             child: Padding(
                padding: const EdgeInsetsDirectional.only(
                  start: 24,
                  end: 12,
@@ -152,14 +152,12 @@ class DatePickerHeader extends StatelessWidget {
                  ],
                ),
              ),
-          ],
+           ),
          );
       case Orientation.landscape:
-        return Row(
-          crossAxisAlignment: CrossAxisAlignment.start,
-          children: <Widget>[
-            Container(
+        return SizedBox(
           width: _datePickerHeaderLandscapeWidth,
+          child: Material(
             color: primarySurfaceColor,
             child: Column(
               crossAxisAlignment: CrossAxisAlignment.start,
@@ -189,7 +187,6 @@ class DatePickerHeader extends StatelessWidget {
               ],
             ),
           ),
-          ],
         );
     }
     return null;

packages/flutter/test/material/date_picker_test.dart

@@ -803,8 +803,7 @@ void main() {
 
       await prepareDatePicker(tester, (Future<DateTime> date) async {
         // Header
-        expect(
-            tester.getSemantics(find.text('SELECT DATE')), matchesSemantics(
+        expect(tester.getSemantics(find.text('SELECT DATE')), matchesSemantics(
           label: 'SELECT DATE\nFri, Jan 15',
         ));
 
@@ -819,8 +818,7 @@ void main() {
         ));
 
         // Year mode drop down button
-        expect(
-            tester.getSemantics(find.text('January 2016')), matchesSemantics(
+        expect(tester.getSemantics(find.text('January 2016')), matchesSemantics(
           label: 'Select year',
           isButton: true,
         ));
@@ -983,7 +981,6 @@ void main() {
           hasEnabledState: true,
           isFocusable: true,
         ));
-
       });
 
       semantics.dispose();
@@ -1107,6 +1104,63 @@ void main() {
     });
   });
 
+  group('Keyboard navigation', () {
+    testWidgets('Can toggle to calendar entry mode', (WidgetTester tester) async {
+      await prepareDatePicker(tester, (Future<DateTime> date) async {
+        expect(find.byType(TextField), findsNothing);
+        // Navigate to the entry toggle button and activate it
+        await tester.sendKeyEvent(LogicalKeyboardKey.tab);
+        await tester.sendKeyEvent(LogicalKeyboardKey.tab);
+        await tester.sendKeyEvent(LogicalKeyboardKey.tab);
+        await tester.sendKeyEvent(LogicalKeyboardKey.tab);
+        await tester.sendKeyEvent(LogicalKeyboardKey.space);
+        await tester.pumpAndSettle();
+        // Should be in the input mode
+        expect(find.byType(TextField), findsOneWidget);
+      });
+    });
+
+    testWidgets('Can toggle to year mode', (WidgetTester tester) async {
+      await prepareDatePicker(tester, (Future<DateTime> date) async {
+        expect(find.text('2016'), findsNothing);
+        // Navigate to the year selector and activate it
+        await tester.sendKeyEvent(LogicalKeyboardKey.tab);
+        await tester.sendKeyEvent(LogicalKeyboardKey.space);
+        await tester.pumpAndSettle();
+        // The years should be visible
+        expect(find.text('2016'), findsOneWidget);
+      });
+    });
+
+    testWidgets('Can navigate next/previous months', (WidgetTester tester) async {
+      await prepareDatePicker(tester, (Future<DateTime> date) async {
+        expect(find.text('January 2016'), findsOneWidget);
+        // Navigate to the previous month button and activate it twice
+        await tester.sendKeyEvent(LogicalKeyboardKey.tab);
+        await tester.sendKeyEvent(LogicalKeyboardKey.tab);
+        await tester.sendKeyEvent(LogicalKeyboardKey.space);
+        await tester.pumpAndSettle();
+        await tester.sendKeyEvent(LogicalKeyboardKey.space);
+        await tester.pumpAndSettle();
+        // Should be showing Nov 2015
+        expect(find.text('November 2015'), findsOneWidget);
+
+        // Navigate to the next month button and activate it four times
+        await tester.sendKeyEvent(LogicalKeyboardKey.tab);
+        await tester.sendKeyEvent(LogicalKeyboardKey.space);
+        await tester.pumpAndSettle();
+        await tester.sendKeyEvent(LogicalKeyboardKey.space);
+        await tester.pumpAndSettle();
+        await tester.sendKeyEvent(LogicalKeyboardKey.space);
+        await tester.pumpAndSettle();
+        await tester.sendKeyEvent(LogicalKeyboardKey.space);
+        await tester.pumpAndSettle();
+        // Should be on Mar 2016
+        expect(find.text('March 2016'), findsOneWidget);
+      });
+    });
+  });
+
   group('Screen configurations', () {
     // Test various combinations of screen sizes, orientations and text scales
     // to ensure the layout doesn't overflow and cause an exception to be thrown.