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add forceErrorText to FormField & TextFormField. (#132903)

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Introducing the `forceErrorText` property to both `FormField` and `TextFormField`. With this addition, we gain the capability to trigger an error state and provide an error message without invoking the `validator` method.

While the idea of making the `Validator` method work asynchronously may be appealing, it could introduce significant complexity to our current form field implementation. Additionally, this approach might not be suitable for all developers, as discussed by @justinmc  in this [comment](https://github.com/flutter/flutter/issues/56414#issuecomment-624960263).

This PR try to address this issue by adding `forceErrorText` property allowing us to force the error to the `FormField` or `TextFormField` at our own base making it possible to preform some async operations without the need for any hacks while keep the ability to check for errors if we call `formKey.currentState!.validate()`.

Here is an example:

<details> <summary>Code Example</summary>  

```dart
import 'package:flutter/material.dart';

void main() {
  runApp(
    const MaterialApp(home: MyHomePage()),
  );
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({
    super.key,
  });

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  final key = GlobalKey<FormState>();
  String? forcedErrorText;

  Future<void> handleValidation() async {
    // simulate some async work..
    await Future.delayed(const Duration(seconds: 3));

    setState(() {
      forcedErrorText = 'this username is not available.';
    });

    // wait for build to run and then check.
    //
    // this is not required though, as the error would already be showing.
    WidgetsBinding.instance.addPostFrameCallback((_) {
      print(key.currentState!.validate());
    });
  }

  @override
  Widget build(BuildContext context) {
    print('build');
    return Scaffold(
      floatingActionButton: FloatingActionButton(onPressed: handleValidation),
      body: Form(
        key: key,
        child: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              Padding(
                padding: const EdgeInsets.symmetric(horizontal: 30),
                child: TextFormField(
                  forceErrorText: forcedErrorText,
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }
}
```
</details>

Related to #9688 & #56414.

Happy to hear your thoughts on this.
This commit is contained in:
Hasan M. Hallak
2024-06-18 20:52:21 +03:00
committed by GitHub
parent 6c06abbb55
commit f54dfcd27d
6 changed files with 520 additions and 13 deletions
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138
examples/api/lib/material/text_form_field/text_form_field.2.dart Normal file
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// 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/material.dart';
/// Flutter code sample for [TextFormField].
const Duration kFakeHttpRequestDuration = Duration(seconds: 3);
void main() => runApp(const TextFormFieldExampleApp());
class TextFormFieldExampleApp extends StatelessWidget {
const TextFormFieldExampleApp({super.key});
@override
Widget build(BuildContext context) {
return const MaterialApp(
home: TextFormFieldExample(),
);
}
}
class TextFormFieldExample extends StatefulWidget {
const TextFormFieldExample({super.key});
@override
State<TextFormFieldExample> createState() => _TextFormFieldExampleState();
}
class _TextFormFieldExampleState extends State<TextFormFieldExample> {
final TextEditingController controller = TextEditingController();
final GlobalKey<FormState> formKey = GlobalKey<FormState>();
String? forceErrorText;
bool isLoading = false;
@override
void dispose() {
controller.dispose();
super.dispose();
}
String? validator(String? value) {
if (value == null || value.isEmpty) {
return 'This field is required';
}
if (value.length != value.replaceAll(' ', '').length) {
return 'Username must not contain any spaces';
}
if (int.tryParse(value[0]) != null) {
return 'Username must not start with a number';
}
if (value.length <= 2) {
return 'Username should be at least 3 characters long';
}
return null;
}
void onChanged(String value) {
// Nullify forceErrorText if the input changed.
if (forceErrorText != null) {
setState(() {
forceErrorText = null;
});
}
}
Future<void> onSave() async {
// Providing a default value in case this was called on the
// first frame, the [fromKey.currentState] will be null.
final bool isValid = formKey.currentState?.validate() ?? false;
if (!isValid) {
return;
}
setState(() => isLoading = true);
final String? errorText = await validateUsernameFromServer(controller.text);
if (context.mounted) {
setState(() => isLoading = false);
if (errorText != null) {
setState(() {
forceErrorText = errorText;
});
}
}
}
@override
Widget build(BuildContext context) {
return Material(
child: Padding(
padding: const EdgeInsets.symmetric(horizontal: 24.0),
child: Center(
child: Form(
key: formKey,
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
TextFormField(
forceErrorText: forceErrorText,
controller: controller,
decoration: const InputDecoration(
hintText: 'Please write a username',
),
validator: validator,
onChanged: onChanged,
),
const SizedBox(height: 40.0),
if (isLoading)
const CircularProgressIndicator()
else
TextButton(
onPressed: onSave,
child: const Text('Save'),
),
],
),
),
),
),
);
}
}
Future<String?> validateUsernameFromServer(String username) async {
final Set<String> takenUsernames = <String>{'jack', 'alex'};
await Future<void>.delayed(kFakeHttpRequestDuration);
final bool isValid = !takenUsernames.contains(username);
if (isValid) {
return null;
}
return 'Username $username is already taken';
}

82
examples/api/test/material/text_form_field/text_form_field.2_test.dart Normal file
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// 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/material.dart';
import 'package:flutter_api_samples/material/text_form_field/text_form_field.2.dart' as example;
import 'package:flutter_test/flutter_test.dart';
void main() {
group('TextFormFieldExample2 Widget Tests', () {
testWidgets('Input validation handles empty, incorrect, and short usernames', (WidgetTester tester) async {
await tester.pumpWidget(const example.TextFormFieldExampleApp());
final Finder textFormField = find.byType(TextFormField);
final Finder saveButton = find.byType(TextButton);
await tester.enterText(textFormField, '');
await tester.pump();
await tester.tap(saveButton);
await tester.pump();
expect(find.text('This field is required'), findsOneWidget);
await tester.enterText(textFormField, 'jo hn');
await tester.tap(saveButton);
await tester.pump();
expect(find.text('Username must not contain any spaces'), findsOneWidget);
await tester.enterText(textFormField, 'jo');
await tester.tap(saveButton);
await tester.pump();
expect(find.text('Username should be at least 3 characters long'), findsOneWidget);
await tester.enterText(textFormField, '1jo');
await tester.tap(saveButton);
await tester.pump();
expect(find.text('Username must not start with a number'), findsOneWidget);
});
testWidgets('Async validation feedback is handled correctly', (WidgetTester tester) async {
await tester.pumpWidget(const example.TextFormFieldExampleApp());
final Finder textFormField = find.byType(TextFormField);
final Finder saveButton = find.byType(TextButton);
// Simulate entering a username already taken.
await tester.enterText(textFormField, 'jack');
await tester.pump();
await tester.tap(saveButton);
await tester.pump();
expect(find.text('Username jack is already taken'), findsNothing);
await tester.pump(example.kFakeHttpRequestDuration);
expect(find.text('Username jack is already taken'), findsOneWidget);
await tester.enterText(textFormField, 'alex');
await tester.pump();
await tester.tap(saveButton);
await tester.pump();
expect(find.text('Username alex is already taken'), findsNothing);
await tester.pump(example.kFakeHttpRequestDuration);
expect(find.text('Username alex is already taken'), findsOneWidget);
await tester.enterText(textFormField, 'jack');
await tester.pump();
await tester.tap(saveButton);
await tester.pump();
expect(find.text('Username jack is already taken'), findsNothing);
await tester.pump(example.kFakeHttpRequestDuration);
expect(find.text('Username jack is already taken'), findsOneWidget);
});
testWidgets('Loading spinner displays correctly when saving', (WidgetTester tester) async {
await tester.pumpWidget(const example.TextFormFieldExampleApp());
final Finder textFormField = find.byType(TextFormField);
final Finder saveButton = find.byType(TextButton);
await tester.enterText(textFormField, 'alexander');
await tester.pump();
await tester.tap(saveButton);
await tester.pump();
expect(find.byType(CircularProgressIndicator), findsOneWidget);
await tester.pump(example.kFakeHttpRequestDuration);
expect(find.byType(CircularProgressIndicator), findsNothing);
});
});
}