Simple Login Register Page in Flutter

main.dart

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: LoginRegisterPage(),
    );
  }
}

enum FormType { Login, Register }

class LoginRegisterPage extends StatefulWidget {
  @override
  _LoginRegisterPageState createState() => _LoginRegisterPageState();
}

class _LoginRegisterPageState extends State<LoginRegisterPage> {
  FormType currentState = FormType.Login;
  final TextEditingController emailController = TextEditingController();
  final TextEditingController passwordController = TextEditingController();
  final TextEditingController usernameController = TextEditingController();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(currentState == FormType.Login ? "Login" : "Register"),
      ),
      body: Container(
        margin: EdgeInsets.all(16),
        child: Column(
          children: <Widget>[
            TextField(
              controller: usernameController,
              decoration: InputDecoration(labelText: 'Username'),
            ),
            currentState == FormType.Register
                ? TextField(
                    controller: emailController,
                    decoration: InputDecoration(labelText: 'Email'),
                  )
                : Container(),
            TextField(
              controller: passwordController,
              decoration: InputDecoration(labelText: 'Password'),
              obscureText: true,
            ),
            SizedBox(
              height: 20,
            ),
            MaterialButton(
                textColor: Colors.white,
                color: Colors.blueAccent,
                child:
                    Text(currentState == FormType.Login ? "Login" : "Register"),
                onPressed: () {
                  if (currentState == FormType.Login) {
                    print(
                        "you are login with id ${usernameController.text} & password ${passwordController.text}");
                  } else {
                    print(
                        "you are register with id ${usernameController.text} , email ${emailController.text} & password ${passwordController.text}");
                  }
                }),
            FlatButton(
              child: Text(currentState == FormType.Register
                  ? 'Have an account? Click here to login.'
                  : 'Don\'nt have an account? Create new Accoun'),
              onPressed: () {
                setState(() {
                  if (currentState == FormType.Login) {
                    currentState = FormType.Register;
                  } else {
                    currentState = FormType.Login;
                  }
                });
              },
            )
          ],
        ),
      ),
    );
  }
}