Técnicas de validação de entrada
Implemente a validação no lado do cliente para campos de formulário usando validadores, expressões regulares e lógica personalizada, garantindo a integridade dos dados.
Técnicas de validação de entrada é uma aula grátis de Flutter Mobile Development no CoddyKit. Esta é a aula 2 de 4. Você pode ler a aula completa abaixo gratuitamente — depois pratica ao vivo no navegador com um editor de código integrado e um tutor de IA 24/7. Faz parte do caminho de aprendizado de Flutter Mobile Development, e seu progresso é sincronizado entre a web e o app CoddyKit. O curso de Flutter Mobile Development inclui 4 aulas no total.
Partes desta aula ainda não foram traduzidas e aparecem em inglês.
What is Input Validation?
When users enter data into your app, you need to make sure it's correct and safe. This process is called input validation.
It's crucial for maintaining data quality and preventing errors or security issues, ensuring your application works as expected.
Why Validate User Input?
Validation helps in many ways to create robust and user-friendly applications:
- Data Integrity: Ensures data fits expected formats (e.g., email looks like an email).
- User Experience: Guides users to enter correct information, reducing frustration.
- Security: Prevents malicious input that could exploit your app (e.g., SQL injection).
- Business Logic: Ensures data meets specific business rules (e.g., age requirements, unique usernames).
The TextFormField Validator
In Flutter, the TextFormField widget has a special property called validator. This property takes a function that checks the input value.
If the input is invalid, the function should return an error message (a String). If it's valid, it should return null.
Basic Empty Field Check
Let's see a simple validator that checks if a text field is empty. If it is, an error message appears below the field.
Try typing something, then deleting it and submitting to see the error.
import 'package:flutter/material.dart';
void main() {
runApp(const MyApp());
}
class MyApp extends StatelessWidget {
const MyApp({super.key});
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Validation Demo',
home: Scaffold(
appBar: AppBar(title: const Text('Basic Validation')),
body: const MyCustomForm(),
),
);
}
}
class MyCustomForm extends StatefulWidget {
const MyCustomForm({super.key});
@override
State<MyCustomForm> createState() => _MyCustomFormState();
}
class _MyCustomFormState extends State<MyCustomForm> {
final _formKey = GlobalKey<FormState>();
@override
Widget build(BuildContext context) {
return Form(
key: _formKey,
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Padding(
padding: const EdgeInsets.all(8.0),
child: TextFormField(
decoration: const InputDecoration(
hintText: 'Enter your name',
labelText: 'Name',
),
validator: (value) {
if (value == null || value.isEmpty) {
return 'Please enter some text';
}
return null;
},
),
),
Padding(
padding: const EdgeInsets.symmetric(vertical: 16.0),
child: ElevatedButton(
onPressed: () {
if (_formKey.currentState!.validate()) {
ScaffoldMessenger.of(context).showSnackBar(
const SnackBar(content: Text('Processing Data')),
);
}
},
child: const Text('Submit'),
),
),
],
),
);
}
}
Displaying Validation Errors
When a validator function returns a String (an error message), the TextFormField automatically displays this message below the input field in a distinct red color.
This immediate visual feedback helps users understand what went wrong and how to fix it, improving the overall user experience.
Custom Logic: Password Check
You can write any custom logic inside your validator function. Here, we check if a password is at least 6 characters long, which is a common security practice.
This demonstrates how to implement rules beyond simple empty checks.
import 'package:flutter/material.dart';
void main() {
runApp(const MyApp());
}
class MyApp extends StatelessWidget {
const MyApp({super.key});
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Validation Demo',
home: Scaffold(
appBar: AppBar(title: const Text('Custom Validation')),
body: const MyCustomForm(),
),
);
}
}
class MyCustomForm extends StatefulWidget {
const MyCustomForm({super.key});
@override
State<MyCustomForm> createState() => _MyCustomFormState();
}
class _MyCustomFormState extends State<MyCustomForm> {
final _formKey = GlobalKey<FormState>();
@override
Widget build(BuildContext context) {
return Form(
key: _formKey,
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Padding(
padding: const EdgeInsets.all(8.0),
child: TextFormField(
obscureText: true,
decoration: const InputDecoration(
hintText: 'Enter a password',
labelText: 'Password',
),
validator: (value) {
if (value == null || value.isEmpty) {
return 'Please enter a password';
}
if (value.length < 6) {
return 'Password must be at least 6 chars';
}
return null;
},
),
),
Padding(
padding: const EdgeInsets.symmetric(vertical: 16.0),
child: ElevatedButton(
onPressed: () {
if (_formKey.currentState!.validate()) {
ScaffoldMessenger.of(context).showSnackBar(
const SnackBar(content: Text('Password is valid!')),
);
}
},
child: const Text('Submit'),
),
),
],
),
);
}
}
Regular Expressions (Regex)
For more complex validation patterns, like checking email formats, phone numbers, or specific alphanumeric sequences, Regular Expressions (Regex) are incredibly powerful.
A regex is a sequence of characters that defines a search pattern. Dart's RegExp class lets you use them easily.
Email Validation with Regex
Here's how to use a simple regular expression to validate an email address format. It checks for a basic pattern: text@text.domain.
Remember, comprehensive email validation can be complex, but this regex provides a good starting point for common formats.
import 'package:flutter/material.dart';
void main() {
runApp(const MyApp());
}
class MyApp extends StatelessWidget {
const MyApp({super.key});
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Regex Validation Demo',
home: Scaffold(
appBar: AppBar(title: const Text('Email Validation')),
body: const MyCustomForm(),
),
);
}
}
class MyCustomForm extends StatefulWidget {
const MyCustomForm({super.key});
@override
State<MyCustomForm> createState() => _MyCustomFormState();
}
class _MyCustomFormState extends State<MyCustomForm> {
final _formKey = GlobalKey<FormState>();
final RegExp emailRegex = RegExp(
r"^[a-zA-Z0-9.]+@[a-zA-Z0-9]+\.[a-zA-Z]+"
);
@override
Widget build(BuildContext context) {
return Form(
key: _formKey,
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Padding(
padding: const EdgeInsets.all(8.0),
child: TextFormField(
keyboardType: TextInputType.emailAddress,
decoration: const InputDecoration(
hintText: 'Enter your email',
labelText: 'Email',
),
validator: (value) {
if (value == null || value.isEmpty) {
return 'Please enter an email';
}
if (!emailRegex.hasMatch(value)) {
return 'Please enter a valid email format';
}
return null;
},
),
),
Padding(
padding: const EdgeInsets.symmetric(vertical: 16.0),
child: ElevatedButton(
onPressed: () {
if (_formKey.currentState!.validate()) {
ScaffoldMessenger.of(context).showSnackBar(
const SnackBar(content: Text('Email is valid!')),
);
}
},
child: const Text('Submit'),
),
),
],
),
);
}
}
Triggering Validation Manually
Validation is typically triggered when the user tries to submit the form. You do this by calling _formKey.currentState!.validate() inside an onPressed handler for a button.
This method runs all validators in the Form and returns true if all are valid, false otherwise. You can also use autovalidateMode on the Form widget to validate inputs as they change, as shown in the example.
import 'package:flutter/material.dart';
void main() {
runApp(const MyApp());
}
class MyApp extends StatelessWidget {
const MyApp({super.key});
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Auto Validate Demo',
home: Scaffold(
appBar: AppBar(title: const Text('Auto-Validation')),
body: const MyCustomForm(),
),
);
}
}
class MyCustomForm extends StatefulWidget {
const MyCustomForm({super.key});
@override
State<MyCustomForm> createState() => _MyCustomFormState();
}
class _MyCustomFormState extends State<MyCustomForm> {
final _formKey = GlobalKey<FormState>();
@override
Widget build(BuildContext context) {
return Form(
key: _formKey,
// Auto-validate as user types
autovalidateMode: AutovalidateMode.always,
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Padding(
padding: const EdgeInsets.all(8.0),
child: TextFormField(
decoration: const InputDecoration(
hintText: 'Enter text (min 3 chars)',
labelText: 'Input',
),
validator: (value) {
if (value == null || value.length < 3) {
return 'Must be at least 3 characters';
}
return null;
},
),
),
Padding(
padding: const EdgeInsets.symmetric(vertical: 16.0),
child: ElevatedButton(
onPressed: () {
// Manual validation still works
if (_formKey.currentState!.validate()) {
ScaffoldMessenger.of(context).showSnackBar(
const SnackBar(content: Text('Input is valid!')),
);
}
},
child: const Text('Submit'),
),
),
],
),
);
}
}
Validation Check
Which of the following are valid ways to implement input validation in Flutter?
Recap: Input Validation
In this lesson, you learned about client-side input validation in Flutter.
- We covered why validation is essential for data integrity, user experience, and security.
- You used the
validatorproperty ofTextFormFieldto define validation rules. - We explored implementing custom logic and using
RegExpfor complex patterns. - Finally, you saw how to trigger validation using
_formKey.currentState!.validate()andautovalidateMode.
Well done! You're now equipped to build more robust and user-friendly forms.
Perguntas Frequentes
A aula “Técnicas de validação de entrada” é grátis?
Sim — o texto completo de “Técnicas de validação de entrada” é grátis para ler aqui na web. Para praticá-la interativamente (um editor de código integrado e um tutor de IA 24/7) e desbloquear o restante do curso de Flutter Mobile Development, atualize para CoddyKit PRO. O curso de Flutter Mobile Development inclui 4 aulas no total.
O que vou aprender em “Técnicas de validação de entrada”?
Implemente a validação no lado do cliente para campos de formulário usando validadores, expressões regulares e lógica personalizada, garantindo a integridade dos dados. Você pratica Flutter Mobile Development com código prático que executa diretamente no navegador, e um tutor de IA 24/7 responde suas dúvidas enquanto trabalha na aula.
Preciso ter experiência prévia para começar Flutter Mobile Development?
Nenhuma experiência prévia é necessária. Flutter Mobile Development no CoddyKit é estruturado para alunos iniciantes até avançados, então você pode começar aqui ou desde o início e aprender no seu ritmo. Esta é a aula 2 de 4.
Quanto tempo leva a aula “Técnicas de validação de entrada”?
A maioria das aulas CoddyKit leva cerca de 5–10 minutos. Cada uma é compacta e interativa, então você faz progresso constante e retoma exatamente de onde parou entre web e app.
Posso escrever e executar código nesta aula de Flutter Mobile Development?
Sim. Cada aula de Flutter Mobile Development inclui um editor de código integrado, então você escreve e executa código real direto no navegador e recebe feedback de IA instantaneamente — nenhuma configuração local necessária.
Todas as aulas deste curso
- Widget Form e controladores
- Técnicas de validação de entrada
- Campos de formulário personalizados
- Foco, Teclado e Experiência de Entrada