How to validate email in a TextFormField

You can use regex for this

Form and TextFormField like so

Form(
  autovalidateMode: AutovalidateMode.always,
  child: TextFormField(
    validator: (value) => validateEmail(value),
  ),
)

then the validation function

String validateEmail(String? value) {
    String pattern =
        r"^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]"
        r"{0,253}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]"
        r"{0,253}[a-zA-Z0-9])?)*$";
    RegExp regex = RegExp(pattern);
    if (value == null || value.isEmpty || !regex.hasMatch(value))
      return 'Enter a valid email address';
    else
      return null;
  }

To validate the form, you can use the autovalidate flag and set up a validator for email. There are many options, including regex or manually writing your own checker, but there are also packages available which implement email checking already.

For example, https://pub.dev/packages/email_validator.

To use it, add it to your pubspec:

dependencies:
  email_validator: '^1.0.0'

import 'package:email_validator/email_validator.dart';

...

Form(
  autovalidate: true,
  child: TextFormField(
    validator: (value) => EmailValidator.validate(value) ? null : "Please enter a valid email",
  ),
)

There are many other validation packages, some of which support may different types of validation. See this search for more https://pub.dev/packages?q=email+validation.

  TextFormField(
          validator: (val) => val.isEmpty || !val.contains("@")
              ? "enter a valid eamil"
              : null,
         
          decoration: InputDecoration(hintText: 'email'),
        ),

In the validator first we are checking if the formfeild is empty and also we are checking if the text entered dose not contains "@" in it . If those conditions are true then we are returning a text "enter a valid email" or else we are not returning anything

I suggest use of this excellent library called validators

1. Add dependency to your package's pubspec.yaml file:

    dependencies:
      validators: ^2.0.0 # change to latest version

2. Run from the command line:

    $ pub get
    // on VSCode u need not do anything.

3. Import in your Dart code:

    import 'package:validators/validators.dart';

4. Validate your field

Form(
  child: TextFormField(
    validator: (val) => !isEmail(val) ? "Invalid Email" : null;,
  ),
)

The previous answers all discuss options for verifying a TextFormField in a Form. The question asks about doing this in

TextFormField or TextField

TextField does not support the validator: named parameter but you can use any of the previously mentioned techniques to check the validity of the email every time the user modifies the email address text. Here is a simple example:

  TextField(
    keyboardType: TextInputType.emailAddress,
    textAlign: TextAlign.center,
    onChanged: (value) {
      setState(() {
        _email = value;
        _emailOk = EmailValidator.validate(_email);
      });
    },
    decoration:
        kTextFieldDecoration.copyWith(hintText: 'Enter your email'),
  ),

You can use the validation result as you see fit. One possibility is to keep a login button deactivated until a valid email address has been entered:

  ElevatedButton(
    child: Text('Log In'),
    // button is disabled until something has been entered in both fields.
    onPressed: (_passwordOk && _emailOk) ? ()=> _logInPressed() : null,
  ),

No need to use external libraries or Regex! Put your text field inside a form, set autovalidate to 'always' and inside TextFormField add a validator function:

 Form(
  autovalidateMode: AutovalidateMode.always,
  child: TextFormField(
    validator: validateEmail,
  ),
)

Validator function:

 String? validateEmail(String? value) {    
      if (value != null) {
        if (value.length > 5 && value.contains('@') && value.endsWith('.com')) {
          return null;
        }
     return 'Enter a Valid Email Address';
    }

note: length > 5 because '.com' and '@' make 5 characters.

QUICK FIX Use this in your TextFormField.

validator: (value) {
  if(value == null || value.isEmpty || !value.contains('@') || !value.contains('.')){
    return 'Invalid Email';
  }
  return null;
},

If you use flutter_form_builder with flutter_builder_validators

email verification can be done easily

FormBuilderTextField(
  name: 'email',
  decoration: InputDecoration(
    labelText: 'Email',
    errorText: _emailError,
  ),
  validator: FormBuilderValidators.compose([
      FormBuilderValidators.required(),
      FormBuilderValidators.email(),
  ]),
),