How to validate the TextFormField as we type in the input in Flutter - flutter

Question

I have created a login screen with textformfield for email id and password using flutter. Also, I have added the validation to check these fields. The code is as below;
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
home: HomePage(),
theme: ThemeData(
brightness: Brightness.dark,
),
);
}
}
class HomePage extends StatefulWidget {
#override
_HomePageState createState() => _HomePageState();
}
class _HomePageState extends State<HomePage> {
var _formKey = GlobalKey<FormState>();
var isLoading = false;
void _submit() {
final isValid = _formKey.currentState.validate();
if (!isValid) {
return;
}
_formKey.currentState.save();
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("Form Validation"),
leading: Icon(Icons.filter_vintage),
),
//body
body: Padding(
padding: const EdgeInsets.all(16.0),
//form
child: Form(
key: _formKey,
child: Column(
children: <Widget>[
Text(
"Form-Validation In Flutter ",
style: TextStyle(fontSize: 24.0, fontWeight: FontWeight.bold),
),
//styling
SizedBox(
height: MediaQuery.of(context).size.width * 0.1,
),
TextFormField(
decoration: InputDecoration(labelText: 'E-Mail'),
keyboardType: TextInputType.emailAddress,
onFieldSubmitted: (value) {
//Validator
},
validator: (value) {
if (value.isEmpty ||
!RegExp(r"^[a-zA-Z0-9.a-zA-Z0-9.!#$%&'*+-/=?^_`{|}~]+#[a-zA-Z0-9]+\.[a-zA-Z]+")
.hasMatch(value)) {
return 'Enter a valid email!';
}
return null;
},
),
//box styling
SizedBox(
height: MediaQuery.of(context).size.width * 0.1,
),
//text input
TextFormField(
decoration: InputDecoration(labelText: 'Password'),
keyboardType: TextInputType.emailAddress,
onFieldSubmitted: (value) {},
obscureText: true,
validator: (value) {
if (value.isEmpty) {
return 'Enter a valid password!';
}
return null;
},
),
SizedBox(
height: MediaQuery.of(context).size.width * 0.1,
),
RaisedButton(
padding: EdgeInsets.symmetric(
vertical: 10.0,
horizontal: 15.0,
),
child: Text(
"Submit",
style: TextStyle(
fontSize: 24.0,
),
),
onPressed: () => _submit(),
)
],
),
),
),
);
}
}
The issue I am facing is, I want to validate the fields as soon as the user starts typing the input(dynamically) rather than clicking on the submit button to wait for the validation to happen. I did a lot of research yet could not find a solution. Thanks in advance for any help!

Answer 1

Flutter Form Validation with TextFormField
Here's an alternative implementation of the _TextSubmitWidgetState that uses a Form:
class _TextSubmitWidgetState extends State<TextSubmitForm> {
// declare a GlobalKey
final _formKey = GlobalKey<FormState>();
// declare a variable to keep track of the input text
String _name = '';
void _submit() {
// validate all the form fields
if (_formKey.currentState!.validate()) {
// on success, notify the parent widget
widget.onSubmit(_name);
}
}
#override
Widget build(BuildContext context) {
// build a Form widget using the _formKey created above.
return Form(
key: _formKey,
child: Column(
mainAxisSize: MainAxisSize.min,
crossAxisAlignment: CrossAxisAlignment.stretch,
children: [
TextFormField(
decoration: const InputDecoration(
labelText: 'Enter your name',
),
// use the validator to return an error string (or null) based on the input text
validator: (text) {
if (text == null || text.isEmpty) {
return 'Can\'t be empty';
}
if (text.length < 4) {
return 'Too short';
}
return null;
},
// update the state variable when the text changes
onChanged: (text) => setState(() => _name = text),
),
ElevatedButton(
// only enable the button if the text is not empty
onPressed: _name.isNotEmpty ? _submit : null,
child: Text(
'Submit',
style: Theme.of(context).textTheme.headline6,
),
),
],
),
);
}
}
source : https://codewithandrea.com/articles/flutter-text-field-form-validation/

Answer 2

May be this can help someone. Inside the TextFormField use this line of code:
autovalidateMode: AutovalidateMode.onUserInteraction

Answer 3

use autovalidateMode in your Form widget
Form(
key: _formKey,
autovalidateMode: AutovalidateMode.onUserInteraction,
child: FormUI(),
),