Feat: `showDatePicker` - Exposed callback when user changes Date Picker Mode (#119116)

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

@@ -164,6 +164,7 @@ Future<DateTime?> showDatePicker({
   String? fieldLabelText,
   TextInputType? keyboardType,
   Offset? anchorPoint,
+  final ValueChanged<DatePickerEntryMode>? onDatePickerModeChange
 }) async {
   initialDate = DateUtils.dateOnly(initialDate);
   firstDate = DateUtils.dateOnly(firstDate);
@@ -202,6 +203,7 @@ Future<DateTime?> showDatePicker({
     fieldHintText: fieldHintText,
     fieldLabelText: fieldLabelText,
     keyboardType: keyboardType,
+    onDatePickerModeChange: onDatePickerModeChange,
   );
 
   if (textDirection != null) {
@@ -259,6 +261,7 @@ class DatePickerDialog extends StatefulWidget {
     this.fieldLabelText,
     this.keyboardType,
     this.restorationId,
+    this.onDatePickerModeChange
   }) : initialDate = DateUtils.dateOnly(initialDate),
        firstDate = DateUtils.dateOnly(firstDate),
        lastDate = DateUtils.dateOnly(lastDate),
@@ -356,6 +359,15 @@ class DatePickerDialog extends StatefulWidget {
   ///    Flutter.
   final String? restorationId;
 
+
+  /// Called when the [DatePickerDialog] is toggled between
+  /// [DatePickerEntryMode.calendar],[DatePickerEntryMode.input].
+  ///
+  /// An example of how this callback might be used is an app that saves the
+  /// user's preferred entry mode and uses it to initialize the
+  /// `initialEntryMode` parameter the next time the date picker is shown.
+  final ValueChanged<DatePickerEntryMode>? onDatePickerModeChange;
+
   @override
   State<DatePickerDialog> createState() => _DatePickerDialogState();
 }
@@ -394,16 +406,24 @@ class _DatePickerDialogState extends State<DatePickerDialog> with RestorationMix
     Navigator.pop(context);
   }
 
+  void _handleOnDatePickerModeChange() {
+    if (widget.onDatePickerModeChange != null) {
+      widget.onDatePickerModeChange!(_entryMode.value);
+    }
+  }
+
   void _handleEntryModeToggle() {
     setState(() {
       switch (_entryMode.value) {
         case DatePickerEntryMode.calendar:
           _autovalidateMode.value = AutovalidateMode.disabled;
           _entryMode.value = DatePickerEntryMode.input;
+          _handleOnDatePickerModeChange();
           break;
         case DatePickerEntryMode.input:
           _formKey.currentState!.save();
           _entryMode.value = DatePickerEntryMode.calendar;
+           _handleOnDatePickerModeChange();
           break;
         case DatePickerEntryMode.calendarOnly:
         case DatePickerEntryMode.inputOnly:

packages/flutter/test/material/date_picker_test.dart

@@ -20,6 +20,7 @@ void main() {
   late SelectableDayPredicate? selectableDayPredicate;
   late DatePickerEntryMode initialEntryMode;
   late DatePickerMode initialCalendarMode;
+  late DatePickerEntryMode currentMode;
 
   String? cancelText;
   String? confirmText;
@@ -56,6 +57,7 @@ void main() {
     fieldLabelText = null;
     helpText = null;
     keyboardType = null;
+    currentMode = initialEntryMode;
   });
 
   Future<void> prepareDatePicker(
@@ -101,6 +103,9 @@ void main() {
       fieldLabelText: fieldLabelText,
       helpText: helpText,
       keyboardType: keyboardType,
+      onDatePickerModeChange: (DatePickerEntryMode value) {
+        currentMode = value;
+      },
       builder: (BuildContext context, Widget? child) {
         return Directionality(
           textDirection: textDirection,
@@ -1369,6 +1374,19 @@ void main() {
     expect(find.byType(TextField), findsNothing);
     expect(find.byIcon(Icons.edit), findsNothing);
   }, skip: isBrowser); // https://github.com/flutter/flutter/issues/33615
+
+  testWidgets('Test Callback on Toggle of DatePicker Mode', (WidgetTester tester) async {
+    prepareDatePicker(tester, (Future<DateTime?> date) async {
+      await tester.tap(find.byIcon(Icons.edit));
+      expect(currentMode, DatePickerEntryMode.input);
+      await tester.pumpAndSettle();
+      expect(find.byType(TextField), findsOneWidget);
+      await tester.tap(find.byIcon(Icons.calendar_today));
+      expect(currentMode, DatePickerEntryMode.calendar);
+      await tester.pumpAndSettle();
+      expect(find.byType(TextField), findsNothing);
+    });
+  });
 }
 
 class _RestorableDatePickerDialogTestWidget extends StatefulWidget {