Validation with dependency between fields did not happen as expected

[ErliSoares]

Steps to Reproduce

1. Run the code below
2. Click the validate button
3. Uncheck the "Field Is Required" checkbox

code sample

import 'package:flutter/material.dart';

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

class MyWidget extends StatefulWidget {
  @override
  _MyWidgetState createState() => _MyWidgetState();
}

class _MyWidgetState extends State<MyWidget> {
  GlobalKey<FormState> _formKey;
  bool _required = true;

  @override
  void initState() {
    super.initState();
    _formKey = GlobalKey<FormState>();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Form(
        key: _formKey,
        child: Column(
          children: [
            CheckboxListTile(
              title: const Text('Field Is Required'),
              value: _required,
              onChanged: (value) {
                setState(() {
                  _required = value;
                });
              },
            ),
            RaisedButton(
              child: const Text('Validate'),
              onPressed: () {
                _formKey.currentState.validate();
              },
            ),
            TextFormField(
              autovalidateMode: AutovalidateMode.onUserInteraction,
              decoration: const InputDecoration(labelText: 'Field 1'),
              validator: (value) {
                if (value == '' && _required) {
                  return 'Error';
                }
                return null;
              },
            ),
          ],
        ),
      ),
    );
  }
}

Expected results: As the field looks like AutovalidateMode.onUserInteraction I expected the field to be revalidated and the error removed.

I had to create another component for the field to self-validate, something like _hasInteractedByUser = true; in the block below would solve

flutter/packages/flutter/lib/src/widgets/form.dart

Lines 459 to 464 in 357dcc9

	bool validate() {
	setState(() {
	_validate();
	});
	return !hasError;
	}

Actual results: As the field has not been changed by the user, the field is not revalidated.

flutter doctor -v

[√] Flutter (Channel stable, 1.22.5, on Microsoft Windows [Version 10.0.19042.746], locale pt-BR)
    • Flutter version 1.22.5 at C:\src\flutter
    • Framework revision 7891006299 (7 weeks ago), 2020-12-10 11:54:40 -0800
    • Engine revision ae90085a84
    • Dart version 2.10.4


[√] Android toolchain - develop for Android devices (Android SDK version 30.0.0-rc1)
    • Android SDK at D:\AndroidSdk
    • Platform android-30, build-tools 30.0.0-rc1
    • ANDROID_HOME = D:\AndroidSdk
    • ANDROID_SDK_ROOT = D:\AndroidSdk
    • Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b01)
    • All Android licenses accepted.

[!] Android Studio (version 4.1.0)
    • Android Studio at C:\Program Files\Android\Android Studio
    X Flutter plugin not installed; this adds Flutter specific functionality.
    X Dart plugin not installed; this adds Dart specific functionality.
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b01)

[!] VS Code (version 1.52.1)
    • VS Code at C:\Users\erli\AppData\Local\Programs\Microsoft VS Code
    X Flutter extension not installed; install from
      https://marketplace.visualstudio.com/items?itemName=Dart-Code.flutter

[√] Connected device (1 available)
    • SM M315F (mobile) • RX8N80DL2NK • android-arm64 • Android 10 (API 29)

! Doctor found issues in 2 categories.

[pedromassangocode]

Hi @ErliSoares
The field will be autovalidate only if AutovalidateMode.onUserInteraction is set however you are validating it through a Form widget so you need to tell that Form widget what is the auto validation policy to validate its fields.

You should set the autovalidateMode in the Form widget to AutovalidateMode.onUserInteraction. I've updated your code and here is how it behaves:

Is this what you are trying to achieve? If not feel free to write in the comments bellow and I will reopen it.
Thank you

updated code sample

import 'package:flutter/material.dart';

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

class MyWidget extends StatefulWidget {
  @override
  _MyWidgetState createState() => _MyWidgetState();
}

class _MyWidgetState extends State<MyWidget> {
  GlobalKey<FormState> _formKey;
  bool _required = true;

  @override
  void initState() {
    super.initState();
    _formKey = GlobalKey<FormState>();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Form(
        key: _formKey,
        autovalidateMode: AutovalidateMode.onUserInteraction,
        child: Column(
          children: [
            CheckboxListTile(
              title: const Text('Field Is Required'),
              value: _required,
              onChanged: (value) {
                setState(() {
                  _required = value;
                });
              },
            ),
            RaisedButton(
              child: const Text('Validate'),
              onPressed: () {
                _formKey.currentState.validate();
              },
            ),
            TextFormField(
              autovalidateMode: AutovalidateMode.onUserInteraction,
              decoration: const InputDecoration(labelText: 'Field 1'),
              validator: (value) {
                if (value == '' && _required) {
                  return 'Error';
                }
                return null;
              },
            ),
          ],
        ),
      ),
    );
  }
}

[ErliSoares]

Thank you very much, solve the problem.
A note in this approach is that when changing a field, all will be revalidated, with the custom component that I made before knowing this solution, only those that were modified by the user or had an error are revalidated.

[github-actions]

This thread has been automatically locked since there has not been any recent activity after it was closed. If you are still experiencing a similar issue, please open a new bug, including the output of flutter doctor -v and a minimal reproduction of the issue.