Include validation for inputOnly mode (#78428)

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

@@ -306,7 +306,7 @@ class _DatePickerDialogState extends State<_DatePickerDialog> {
   }
 
   void _handleOk() {
-    if (_entryMode == DatePickerEntryMode.input) {
+    if (_entryMode == DatePickerEntryMode.input || _entryMode == DatePickerEntryMode.inputOnly) {
       final FormState form = _formKey.currentState!;
       if (!form.validate()) {
         setState(() => _autoValidate = true);
@@ -972,7 +972,7 @@ class _DateRangePickerDialogState extends State<_DateRangePickerDialog> {
   }
 
   void _handleOk() {
-    if (_entryMode == DatePickerEntryMode.input) {
+    if (_entryMode == DatePickerEntryMode.input || _entryMode == DatePickerEntryMode.inputOnly) {
       final _InputDateRangePickerState picker = _inputPickerKey.currentState!;
       if (!picker.validate()) {
         setState(() {

packages/flutter/test/material/date_picker_test.dart

@@ -177,6 +177,17 @@ void main() {
       });
     });
 
+    testWidgets('Input only mode should validate date', (WidgetTester tester) async {
+      initialEntryMode = DatePickerEntryMode.inputOnly;
+      await prepareDatePicker(tester, (Future<DateTime?> date) async {
+        // Enter text input mode and type an invalid date to get error.
+        await tester.enterText(find.byType(TextField), '1234567');
+        await tester.tap(find.text('OK'));
+        await tester.pumpAndSettle();
+        expect(find.text('Invalid format.'), findsOneWidget);
+      });
+    });
+
     testWidgets('Switching to input mode resets input error state', (WidgetTester tester) async {
       await prepareDatePicker(tester, (Future<DateTime?> date) async {
         // Enter text input mode and type an invalid date to get error.

packages/flutter/test/material/date_range_picker_test.dart

@@ -266,6 +266,20 @@ void main() {
     });
   });
 
+  testWidgets('Input only mode should validate date', (WidgetTester tester) async {
+    initialEntryMode = DatePickerEntryMode.inputOnly;
+    errorInvalidText = 'oops';
+    await preparePicker(tester, (Future<DateTimeRange?> range) async {
+      await tester.enterText(find.byType(TextField).at(0), '08/08/2014');
+      await tester.enterText(find.byType(TextField).at(1), '08/08/2014');
+      expect(find.text(errorInvalidText!), findsNothing);
+
+      await tester.tap(find.text('OK'));
+      await tester.pumpAndSettle();
+      expect(find.text(errorInvalidText!), findsNWidgets(2));
+    });
+  });
+
   testWidgets('Switching to input mode keeps selected date', (WidgetTester tester) async {
     await preparePicker(tester, (Future<DateTimeRange?> range) async {
       await tester.tap(find.text('12').first);