Validate and customize TextFormFields in Flutter (tutorial with source code)

There are many ways to build forms with validation in Flutter, including using third-party packages. But why depend on external packages when you can achieve a lot with just the built-in Form and TextFormField widgets? This article will demonstrate the powerful customizability and robustness of Flutter itself, allowing you to build forms using TextFormFields with custom appearance, while implementing complex validation logic without relying on external packages.

Form and TextField What is TextFormField?

Form: group and validate multiple form fields

TextField: accepts text input

TextFormField: TextField is validated

Basic Authentication Techniques

The most basic form of validation can be seen in the example here. I've copied some of the examples here for easy reference:

// This class holds data related to the form.
class MyCustomFormState extends State<MyCustomForm> {
  // Create a global key that uniquely identifies the Form widget
  // and allows validation of the form.
  //
  // Note: This is a GlobalKey<FormState>,
  // not a GlobalKey<MyCustomFormState>.
  final _formKey = GlobalKey<FormState>();

  @override
  Widget build(BuildContext context) {
    // Build a Form widget using the _formKey created above.
    return Form(
      key: _formKey,