Getx - Sample Form

main.dart

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

void main() {
  runApp(GetMaterialApp(
    initialRoute: '/login',
    getPages: [
      GetPage(
        name: '/login',
        page: () => LoginPage(),
        binding: LoginBinding(),
      ),
    ],
  ));
}

class LoginBinding implements Bindings {
  @override
  void dependencies() {
    Get.lazyPut(() => LoginController());
  }
}

class LoginController extends GetxController {
  final loginFormKey = GlobalKey<FormState>();
  final emailController = TextEditingController();
  final passwordController = TextEditingController();

  @override
  void onInit() {
    // Simulating obtaining the user name from some local storage
    emailController.text = '[email protected]';
    super.onInit();
  }
  
  @override
  void onClose() {
    emailController.dispose();
    passwordController.dispose();
    super.onClose();
  }

  String validator(String value) {
    if (value.isEmpty) {
      return 'Please this field must be filled';
    }
    return null;
  }

  void login() {
    if (loginFormKey.currentState.validate()) {
      checkUser(emailController.text, passwordController.text).then((auth) {
        if (auth) {
          Get.snackbar('Login', 'Login successfully');
        } else {
          Get.snackbar('Login', 'Invalid email or password');
        }
        passwordController.clear();
      });
    }
  }

  // Api Simulation
  Future<bool> checkUser(String user, String password) {
    if (user == '[email protected]' && password == '123') {
      return Future.value(true);
    }
    return Future.value(false);
  }
}

class LoginPage extends GetView<LoginController> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('LOGIN')),
      body: Container(
        padding: const EdgeInsets.all(16.0),
        child: Form(
          key: controller.loginFormKey,
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              TextFormField(
                controller: controller.emailController,
                decoration: const InputDecoration(labelText: 'E-mail'),
                validator: controller.validator,
              ),
              TextFormField(
                controller: controller.passwordController,
                decoration: const InputDecoration(labelText: 'Password'),
                validator: controller.validator,
                obscureText: true,
              ),
              RaisedButton(
                child: Text('Login'),
                onPressed: controller.login,
              )
            ],
          ),
        ),
      ),
    );
  }
}

@eduardoflorence, Thanks for the example, I'm just learning, I know the problem below is due to different flutter version and the null safety feature, but I try everything and still controller.validator is not accepted.

validator: controller.validator,

it is given me this error

Error: The argument type 'String Function(String)' can't be assigned to the parameter type 'String? Function(String?)?' because 'String?' is nullable and 'String' isn't.

@clust3rsekt0r
you can simply change the validator to =>

String? validator(String? value) {
  if (value == null || value.isEmpty) {
    return 'Please this field must be filled';
  }
  return null;
}

and it will work.

you need to check if the value is null before using value.isEmpty

Big thanks

https://stackoverflow.com/a/72657878/1432751

big big big thanks...

thank you