Form

import 'package:flutter/material.dart';
import 'package:flutter/cupertino.dart';

class ShowForm extends StatefulWidget {
  const ShowForm({Key? key}) : super(key: key);

  @override
  _ShowFormState createState() => _ShowFormState();
}

class _ShowFormState extends State<ShowForm> {

  // Controllers for text editing
  final TextEditingController _emailTextController = TextEditingController();
  final _focusEmail = FocusNode();
  final TextEditingController _passwordTextController = TextEditingController();
  final _focusPassword = FocusNode();

  bool _obscurePassword = true;

  // Form management key
  static final GlobalKey<FormState> _formKey = GlobalKey<FormState>();


  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(title: const Text("Form")),
        body: Container(
            padding: const EdgeInsets.all(20),
            alignment: Alignment.center,
            child: Center(
                child: loginForm(context)
            )
        )
    );
  }

  /// **********************************************************************
  /// Sign in form with email/password: 2 TextFormFields and 1 ElevatedButton
  /// **********************************************************************
  Widget loginForm(BuildContext context) {
    return Form(
      key: _formKey,
      child: Column(
        mainAxisSize: MainAxisSize.min,

        children: <Widget>[

          emailInput(context),

          const SizedBox(height: 8.0),

          passwordInput(context),

          const SizedBox(height: 25.0),

          confirmButton(context)

        ],
      ),
    );
  }

  /// **********************************************************************
  /// Email input capture with TextFormField
  /// **********************************************************************
  Widget emailInput(BuildContext context) {
    return TextFormField(
      controller: _emailTextController,
      focusNode: _focusEmail,
      validator: (value) => _validateEmail(context: context, email: value!),
      decoration: InputDecoration(
        hintText: "Email",
        border: const OutlineInputBorder(
            borderRadius: BorderRadius.all(Radius.circular(20),
            )),
        errorBorder: UnderlineInputBorder(
          borderRadius: BorderRadius.circular(6.0),
          borderSide: const BorderSide(
            color: Colors.red,
          ),
        ),
      ),
    );
  }

  /// **********************************************************************
  /// Password input capture with TextFormField
  /// **********************************************************************
  Widget passwordInput(BuildContext context) {
    return TextFormField(
      controller: _passwordTextController,
      focusNode: _focusPassword,
      obscureText: _obscurePassword,
      validator: (value) => _validatePassword(context: context, password: value!),
      decoration: InputDecoration(
          hintText: "Password",
          border: const OutlineInputBorder(
              borderRadius: BorderRadius.all(Radius.circular(20),
              )
          ),
          errorBorder: UnderlineInputBorder(
            borderRadius: BorderRadius.circular(6.0),
            borderSide: const BorderSide(
              color: Colors.red,
            ),
          ),
          suffixIcon: IconButton(
            onPressed: () {
              setState(() {
                _obscurePassword = !_obscurePassword;
              });
            },
            icon: (_obscurePassword)
                ? const Icon(CupertinoIcons.eye_slash_fill)
                : const Icon(CupertinoIcons.eye_fill),
          )
      ),
    );
  }

  /// **********************************************************************
  /// Button to confirm the login details
  /// **********************************************************************
  Widget confirmButton(BuildContext context) {
    return Row(
      children: [
        Expanded(
            child: ElevatedButton(
              onPressed: () => _login(),
              style: ElevatedButton.styleFrom(
                  backgroundColor: Colors.blue,
                  shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(20.0))
              ),

              child: Text("Confirm"),
              ),
            )
        ]
    );
  }

/// **********************************************************************
/// Called when confirmButton is pressed
/// **********************************************************************
Future<void> _login() async {
  _focusEmail.unfocus();
  _focusPassword.unfocus();

  // Validation of all inputs
  if (_formKey.currentState!.validate()) {
    print("Login with email = ${_emailTextController.text} "
        "and password = ${_passwordTextController.text}");
  }
}

  /// **********************************************************************
  /// Checks whether the email address field is empty
  /// and validate format using a regular expression
  /// **********************************************************************
  static String? _validateEmail({required BuildContext context, required String email}) {
    RegExp emailRegExp = RegExp(
        r"^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,253}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,253}[a-zA-Z0-9])?)*$");

    if (email.isEmpty) {
      return "Please enter a valid email address";
    } else if (!emailRegExp.hasMatch(email)) {
      return "Please enter a valid email address";
    }

    return null;
  }

  /// **********************************************************************
  /// Checks whether the password field is empty
  /// and verify that the length is longer than six characters
  /// **********************************************************************
  static String? _validatePassword({required BuildContext context, required String password}) {

    if (password.isEmpty) {
      return "Password must contain at least 6 characters";
    } else if (password.length < 6) {
      return "Password must contain at least 6 characters";
    }

    return null;
  }
}