5 Ways to Implement Email Validation in Flutter

Ensuring user emails are valid is a key part of building reliable Flutter applications. This piece walks through five ways to handle email validation, providing working code for each. We then examine the shortfalls of these common techniques and show how Abstract API overcomes them.

How to Implement Email Validation in Flutter

Here are three common, client-side methods to validate email syntax directly within a Flutter application. Each approach offers a different balance of simplicity, control, and dependency management.

Inline Regular Expression

This pure Dart approach keeps validation stateless and client-side. It involves the creation of a validator from a regular expression pattern that follows the RFC 5322 standard for email syntax. This pattern checks for the correct structure of an email address.

The code defines a global `RegExp` object with the validation pattern. A function then uses this object's `hasMatch` method to check if an input string is a valid email. This function can be passed directly to a `TextFormField` widget's validator property.

final _emailRe = RegExp(
  r'''^(?:(?:[^<>()\[\]\\.,;:\s@"']+(?:\.[^<>()\[\]\\.,;:\s@"']+)*)|".+")@(?:\[[0-9.]+\]|(?:[a-zA-Z0-9-]+\.)+[a-zA-Z]{2,})$'''
);

String? validateEmail(String? v) {
  if (v == null || v.isEmpty) return 'Required';
  return _emailRe.hasMatch(v) ? null : 'Not a valid e-mail';
}
...
TextFormField(validator: validateEmail)

The email_validator Package

A popular alternative is to use the `email_validator` package. This method relies on a purpose-built parser instead of a single regular expression. The package is unit-tested against thousands of cases and covers various formats like dot-atom, quoted strings, and address literals.

After you add the package as a dependency, you can import it and call the static `EmailValidator.validate` method. This method returns a boolean that indicates whether the input string conforms to the correct email syntax. It provides the same results on all platforms.

import 'package:email_validator/email_validator.dart';
...
if (EmailValidator.validate(input)) { … }

A Composable Validator Layer

This method applies the Strategy design pattern to create a flexible validation pipeline. You can use a package like `flutter_easy_validator` or build your own implementation. It allows you to chain multiple independent validation rules together for a single field.

The code shows how to compose a validator that checks for several conditions in sequence. It first confirms the field is not empty, then checks for valid email format, and finally applies a custom rule. This modular approach makes unit tests trivial and simplifies rule management.



TextFormField(validator: validator);

final validator = EasyValidator.compose([
  EasyValidator.required(),
  EasyValidator.email(),            // built-in strategy
  EasyValidator.notStartWith('test')// add your own rule
]).validate;

TextFormField(validator: validator);

Challenges of Email Validation in Flutter

Client-side validation techniques check syntax but overlook deeper issues. These approaches introduce problems with maintainability, future-proofing, and the overall user experience.

• A simple inline regular expression cannot fully parse RFC 5322 standards. It often rejects valid addresses with quoted strings or comments and accepts invalid ones. This makes the pattern difficult to maintain.
• Static client-side methods fail to account for new gTLDs and international domain names. An inline regex or a package with a fixed TLD list quickly becomes outdated and rejects valid, modern email addresses.
• Client-side validation only confirms syntax, not deliverability. Methods like email_validator cannot check for MX records or disposable domains. Synchronous checks on the UI thread cannot perform network calls without application jank.
• A complex inline regular expression can cause performance issues. Certain inputs may trigger catastrophic backtracking in Dart's regex engine, which freezes the user interface and degrades the user experience.