Restorable CupertinoTextFormFieldRow (#144541)

## Description

This PR makes `CupertinoTextFormFieldRow` restorable.
The implementation is based on https://github.com/flutter/flutter/pull/78835 which made `FormField` and `TextFormField` restorable.

## Related Issue

Fixes https://github.com/flutter/flutter/issues/144504.

## Tests

Adds 4 tests.

packages/flutter/lib/src/cupertino/text_form_field_row.dart

@@ -157,6 +157,7 @@ class CupertinoTextFormFieldRow extends FormField<String> {
       color: CupertinoColors.placeholderText,
     ),
     EditableTextContextMenuBuilder? contextMenuBuilder = _defaultContextMenuBuilder,
+    super.restorationId,
   })  : assert(initialValue == null || controller == null),
         assert(obscuringCharacter.length == 1),
         assert(maxLines == null || maxLines > 0),
@@ -186,7 +187,10 @@ class CupertinoTextFormFieldRow extends FormField<String> {
               prefix: prefix,
               padding: padding,
               error: (field.errorText == null) ? null : Text(field.errorText!),
+              child: UnmanagedRestorationScope(
+                bucket: field.bucket,
                 child: CupertinoTextField.borderless(
+                  restorationId: restorationId,
                   controller: state._effectiveController,
                   focusNode: focusNode,
                   keyboardType: keyboardType,
@@ -231,6 +235,7 @@ class CupertinoTextFormFieldRow extends FormField<String> {
                   placeholderStyle: placeholderStyle,
                   contextMenuBuilder: contextMenuBuilder,
                 ),
+              ),
             );
           },
         );
@@ -272,19 +277,45 @@ class CupertinoTextFormFieldRow extends FormField<String> {
 }
 
 class _CupertinoTextFormFieldRowState extends FormFieldState<String> {
-  TextEditingController? _controller;
+  RestorableTextEditingController? _controller;
 
-  TextEditingController? get _effectiveController =>
+  TextEditingController get _effectiveController =>
-      _cupertinoTextFormFieldRow.controller ?? _controller;
+      _cupertinoTextFormFieldRow.controller ?? _controller!.value;
 
   CupertinoTextFormFieldRow get _cupertinoTextFormFieldRow =>
       super.widget as CupertinoTextFormFieldRow;
 
+  @override
+  void restoreState(RestorationBucket? oldBucket, bool initialRestore) {
+    super.restoreState(oldBucket, initialRestore);
+    if (_controller != null) {
+      _registerController();
+    }
+    // This makes sure to update the internal [FormFieldState] value to sync up with
+    // text editing controller value.
+    setValue(_effectiveController.text);
+  }
+
+  void _registerController() {
+    assert(_controller != null);
+    registerForRestoration(_controller!, 'controller');
+  }
+
+  void _createLocalController([TextEditingValue? value]) {
+    assert(_controller == null);
+    _controller = value == null
+        ? RestorableTextEditingController()
+        : RestorableTextEditingController.fromValue(value);
+    if (!restorePending) {
+      _registerController();
+    }
+  }
+
   @override
   void initState() {
     super.initState();
     if (_cupertinoTextFormFieldRow.controller == null) {
-      _controller = TextEditingController(text: widget.initialValue);
+      _createLocalController(widget.initialValue != null ? TextEditingValue(text: widget.initialValue!) : null);
     } else {
       _cupertinoTextFormFieldRow.controller!.addListener(_handleControllerChanged);
     }
@@ -298,13 +329,14 @@ class _CupertinoTextFormFieldRowState extends FormFieldState<String> {
       _cupertinoTextFormFieldRow.controller?.addListener(_handleControllerChanged);
 
       if (oldWidget.controller != null && _cupertinoTextFormFieldRow.controller == null) {
-        _controller =
+        _createLocalController(oldWidget.controller!.value);
-            TextEditingController.fromValue(oldWidget.controller!.value);
       }
 
       if (_cupertinoTextFormFieldRow.controller != null) {
         setValue(_cupertinoTextFormFieldRow.controller!.text);
         if (oldWidget.controller == null) {
+          unregisterFromRestoration(_controller!);
+          _controller!.dispose();
           _controller = null;
         }
       }
@@ -322,8 +354,8 @@ class _CupertinoTextFormFieldRowState extends FormFieldState<String> {
   void didChange(String? value) {
     super.didChange(value);
 
-    if (value != null && _effectiveController!.text != value) {
+    if (value != null && _effectiveController.text != value) {
-      _effectiveController!.text = value;
+      _effectiveController.text = value;
     }
   }
 
@@ -331,9 +363,9 @@ class _CupertinoTextFormFieldRowState extends FormFieldState<String> {
   void reset() {
     // Set the controller value before calling super.reset() to let
     // _handleControllerChanged suppress the change.
-    _effectiveController!.text = widget.initialValue!;
+    _effectiveController.text = widget.initialValue!;
     super.reset();
-    _cupertinoTextFormFieldRow.onChanged?.call(_effectiveController!.text);
+    _cupertinoTextFormFieldRow.onChanged?.call(_effectiveController.text);
   }
 
   void _handleControllerChanged() {
@@ -344,8 +376,8 @@ class _CupertinoTextFormFieldRowState extends FormFieldState<String> {
     // notifications for changes originating from within this class -- for
     // example, the reset() method. In such cases, the FormField value will
     // already have been set.
-    if (_effectiveController!.text != value) {
+    if (_effectiveController.text != value) {
-      didChange(_effectiveController!.text);
+      didChange(_effectiveController.text);
     }
   }
 }

packages/flutter/test/cupertino/text_form_field_row_restoration_test.dart

@@ -0,0 +1,251 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/cupertino.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+const String text = 'Hello World! How are you? Life is good!';
+const String alternativeText = 'Everything is awesome!!';
+
+void main() {
+  testWidgets('CupertinoTextFormFieldRow restoration', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const CupertinoApp(
+        restorationScopeId: 'app',
+        home: RestorableTestWidget(),
+      ),
+    );
+
+    await restoreAndVerify(tester);
+  });
+
+  testWidgets('CupertinoTextFormFieldRow restoration with external controller', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const CupertinoApp(
+        restorationScopeId: 'root',
+        home: RestorableTestWidget(
+          useExternalController: true,
+        ),
+      ),
+    );
+
+    await restoreAndVerify(tester);
+  });
+
+  testWidgets('State restoration (No Form ancestor) - onUserInteraction error text validation', (WidgetTester tester) async {
+    String? errorText(String? value) => '$value/error';
+    late GlobalKey<FormFieldState<String>> formState;
+
+    Widget builder() {
+      return CupertinoApp(
+        restorationScopeId: 'app',
+        home: MediaQuery(
+          data: const MediaQueryData(),
+          child: Directionality(
+            textDirection: TextDirection.ltr,
+            child: Center(
+              child: StatefulBuilder(
+                builder: (BuildContext context, StateSetter state) {
+                  formState = GlobalKey<FormFieldState<String>>();
+                  return Material(
+                    child: CupertinoTextFormFieldRow(
+                      key: formState,
+                      autovalidateMode: AutovalidateMode.onUserInteraction,
+                      restorationId: 'text_form_field',
+                      initialValue: 'foo',
+                      validator: errorText,
+                    ),
+                  );
+                },
+              ),
+            ),
+          ),
+        ),
+      );
+    }
+
+    await tester.pumpWidget(builder());
+
+    // No error text is visible yet.
+    expect(find.text(errorText('foo')!), findsNothing);
+
+    await tester.enterText(find.byType(CupertinoTextFormFieldRow), 'bar');
+    await tester.pumpAndSettle();
+    expect(find.text(errorText('bar')!), findsOneWidget);
+
+    final TestRestorationData data = await tester.getRestorationData();
+    await tester.restartAndRestore();
+    // Error text should be present after restart and restore.
+    expect(find.text(errorText('bar')!), findsOneWidget);
+
+    // Resetting the form state should remove the error text.
+    formState.currentState!.reset();
+    await tester.pumpAndSettle();
+    expect(find.text(errorText('bar')!), findsNothing);
+    await tester.restartAndRestore();
+    // Error text should still be removed after restart and restore.
+    expect(find.text(errorText('bar')!), findsNothing);
+
+    await tester.restoreFrom(data);
+    expect(find.text(errorText('bar')!), findsOneWidget);
+  });
+
+  testWidgets('State Restoration (No Form ancestor) - validator sets the error text only when validate is called', (WidgetTester tester) async {
+    String? errorText(String? value) => '$value/error';
+    late GlobalKey<FormFieldState<String>> formState;
+
+    Widget builder(AutovalidateMode mode) {
+      return CupertinoApp(
+        restorationScopeId: 'app',
+        home: MediaQuery(
+          data: const MediaQueryData(),
+          child: Directionality(
+            textDirection: TextDirection.ltr,
+            child: Center(
+              child: StatefulBuilder(
+                builder: (BuildContext context, StateSetter state) {
+                  formState = GlobalKey<FormFieldState<String>>();
+                  return Material(
+                    child: CupertinoTextFormFieldRow(
+                      key: formState,
+                      restorationId: 'form_field',
+                      autovalidateMode: mode,
+                      initialValue: 'foo',
+                      validator: errorText,
+                    ),
+                  );
+                },
+              ),
+            ),
+          ),
+        ),
+      );
+    }
+
+    // Start off not autovalidating.
+    await tester.pumpWidget(builder(AutovalidateMode.disabled));
+
+    Future<void> checkErrorText(String testValue) async {
+      formState.currentState!.reset();
+      await tester.pumpWidget(builder(AutovalidateMode.disabled));
+      await tester.enterText(find.byType(CupertinoTextFormFieldRow), testValue);
+      await tester.pump();
+
+      // We have to manually validate if we're not autovalidating.
+      expect(find.text(errorText(testValue)!), findsNothing);
+      formState.currentState!.validate();
+      await tester.pump();
+      expect(find.text(errorText(testValue)!), findsOneWidget);
+      final TestRestorationData data = await tester.getRestorationData();
+      await tester.restartAndRestore();
+      // Error text should be present after restart and restore.
+      expect(find.text(errorText(testValue)!), findsOneWidget);
+
+      formState.currentState!.reset();
+      await tester.pumpAndSettle();
+      expect(find.text(errorText(testValue)!), findsNothing);
+
+      await tester.restoreFrom(data);
+      expect(find.text(errorText(testValue)!), findsOneWidget);
+
+      // Try again with autovalidation. Should validate immediately.
+      formState.currentState!.reset();
+      await tester.pumpWidget(builder(AutovalidateMode.always));
+      await tester.enterText(find.byType(CupertinoTextFormFieldRow), testValue);
+      await tester.pump();
+
+      expect(find.text(errorText(testValue)!), findsOneWidget);
+      await tester.restartAndRestore();
+      // Error text should be present after restart and restore.
+      expect(find.text(errorText(testValue)!), findsOneWidget);
+    }
+
+    await checkErrorText('Test');
+    await checkErrorText('');
+  });
+}
+
+Future<void> restoreAndVerify(WidgetTester tester) async {
+  expect(find.text(text), findsNothing);
+  expect(tester.state<ScrollableState>(find.byType(Scrollable)).position.pixels, 0);
+
+  await tester.enterText(find.byType(CupertinoTextFormFieldRow), text);
+  await skipPastScrollingAnimation(tester);
+  expect(tester.state<ScrollableState>(find.byType(Scrollable)).position.pixels, 0);
+
+  await tester.drag(find.byType(Scrollable), const Offset(0, -80));
+  await skipPastScrollingAnimation(tester);
+
+  expect(find.text(text), findsOneWidget);
+  expect(tester.state<ScrollableState>(find.byType(Scrollable)).position.pixels, 60);
+
+  await tester.restartAndRestore();
+
+  expect(find.text(text), findsOneWidget);
+  expect(tester.state<ScrollableState>(find.byType(Scrollable)).position.pixels, 60);
+
+  final TestRestorationData data = await tester.getRestorationData();
+
+  await tester.enterText(find.byType(CupertinoTextFormFieldRow), alternativeText);
+  await skipPastScrollingAnimation(tester);
+  await tester.drag(find.byType(Scrollable), const Offset(0, 80));
+  await skipPastScrollingAnimation(tester);
+
+  expect(find.text(text), findsNothing);
+  expect(tester.state<ScrollableState>(find.byType(Scrollable)).position.pixels, isNot(60));
+
+  await tester.restoreFrom(data);
+
+  expect(find.text(text), findsOneWidget);
+  expect(tester.state<ScrollableState>(find.byType(Scrollable)).position.pixels, 60);
+}
+
+class RestorableTestWidget extends StatefulWidget {
+  const RestorableTestWidget({super.key, this.useExternalController = false});
+
+  final bool useExternalController;
+
+  @override
+  RestorableTestWidgetState createState() => RestorableTestWidgetState();
+}
+
+class RestorableTestWidgetState extends State<RestorableTestWidget> with RestorationMixin {
+  final RestorableTextEditingController controller = RestorableTextEditingController();
+
+  @override
+  String get restorationId => 'widget';
+
+  @override
+  void restoreState(RestorationBucket? oldBucket, bool initialRestore) {
+    registerForRestoration(controller, 'controller');
+  }
+
+  @override
+  void dispose() {
+    controller.dispose();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Material(
+      child: Align(
+        child: SizedBox(
+          width: 50,
+          child: CupertinoTextFormFieldRow(
+            restorationId: 'text',
+            maxLines: 3,
+            controller: widget.useExternalController ? controller.value : null,
+          ),
+        ),
+      ),
+    );
+  }
+}
+
+Future<void> skipPastScrollingAnimation(WidgetTester tester) async {
+  await tester.pump();
+  await tester.pump(const Duration(milliseconds: 200));
+}