Keyboard navigation for the Material Date Picker grid (#59586)

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

@@ -6,7 +6,7 @@
 
 import 'dart:math' as math;
 
-import 'package:flutter/foundation.dart';
+import 'package:flutter/services.dart';
 import 'package:flutter/widgets.dart';
 
 import '../button_bar.dart';
@@ -357,6 +357,11 @@ class _DatePickerDialogState extends State<_DatePickerDialog> {
     return null;
   }
 
+  static final Map<LogicalKeySet, Intent> _formShortcutMap = <LogicalKeySet, Intent>{
+    // Pressing enter on the field will move focus to the next field or control.
+    LogicalKeySet(LogicalKeyboardKey.enter): const NextFocusIntent(),
+  };
+
   @override
   Widget build(BuildContext context) {
     final ThemeData theme = Theme.of(context);
@@ -419,6 +424,8 @@ class _DatePickerDialogState extends State<_DatePickerDialog> {
           child: Container(
             padding: const EdgeInsets.symmetric(horizontal: 24),
             height: orientation == Orientation.portrait ? _inputFormPortraitHeight : _inputFormLandscapeHeight,
+            child: Shortcuts(
+              shortcuts: _formShortcutMap,
               child: Column(
                 children: <Widget>[
                   const Spacer(),
@@ -439,6 +446,7 @@ class _DatePickerDialogState extends State<_DatePickerDialog> {
                 ],
               ),
             ),
+          ),
         );
         entryModeIcon = Icons.calendar_today;
         entryModeTooltip = localizations.calendarModeButtonLabel;

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

@@ -26,12 +26,20 @@ DateTimeRange datesOnly(DateTimeRange range) {
 }
 
 /// Returns true if the two [DateTime] objects have the same day, month, and
-/// year.
+/// year, or are both null.
 bool isSameDay(DateTime dateA, DateTime dateB) {
   return
-    dateA.year == dateB.year &&
-    dateA.month == dateB.month &&
-    dateA.day == dateB.day;
+    dateA?.year == dateB?.year &&
+    dateA?.month == dateB?.month &&
+    dateA?.day == dateB?.day;
+}
+
+/// Returns true if the two [DateTime] objects have the same month, and
+/// year, or are both null.
+bool isSameMonth(DateTime dateA, DateTime dateB) {
+  return
+    dateA?.year == dateB?.year &&
+    dateA?.month == dateB?.month;
 }
 
 /// Determines the number of months between two [DateTime] objects.