import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {

  @override

  Widget build(BuildContext context) {

    return MaterialApp(

      home: HomePage(),

      theme: ThemeData(

        brightness: Brightness.dark,

      ),

    );

  }

}

class HomePage extends StatefulWidget {

  @override

  _HomePageState createState() => _HomePageState();

}

class _HomePageState extends State {

  var _formKey = GlobalKey();

  var isLoading = false;

  void _submit() {

    final isValid = _formKey.currentState.validate();

    if (!isValid) {

      return;

    }

    _formKey.currentState.save();

  }

  @override

  Widget build(BuildContext context) {

    return Scaffold(

      appBar: AppBar(

        title: Text("Form Validation"),

        leading: Icon(Icons.filter_vintage),

      ),

      //body

      body: Padding(

        padding: const EdgeInsets.all(16.0),

        //form

        child: Form(

          key: _formKey,

          child: Column(

            children: [

              Text(

                "Form-Validation In Flutter ",

                style: TextStyle(fontSize: 24.0, fontWeight: FontWeight.bold),

              ),

              //styling

              SizedBox(

                height: MediaQuery.of(context).size.width * 0.1,

              ),

              TextFormField(

                decoration: InputDecoration(labelText: 'E-Mail'),

                keyboardType: TextInputType.emailAddress,

                onFieldSubmitted: (value) {

                  //Validator

                },

                validator: (value) {

                  if (value.isEmpty ||

                      !RegExp(r"^[a-zA-Z0-9.a-zA-Z0-9.!#$%&'*+-/=?^_`{|}~]+@[a-zA-Z0-9]+\.[a-zA-Z]+")

                          .hasMatch(value)) {

                    return 'Enter a valid email!';

                  }

                  return null;

                },

              ),

              //box styling

              SizedBox(

                height: MediaQuery.of(context).size.width * 0.1,

              ),

              //text input 

              TextFormField(

                decoration: InputDecoration(labelText: 'Password'),

                keyboardType: TextInputType.emailAddress,

                onFieldSubmitted: (value) {},

                obscureText: true,

                validator: (value) {

                  if (value.isEmpty) {

                    return 'Enter a valid password!';

                  }

                  return null;

                },

              ),

              SizedBox(

                height: MediaQuery.of(context).size.width * 0.1,

              ),

              RaisedButton(

                padding: EdgeInsets.symmetric(

                  vertical: 10.0,

                  horizontal: 15.0,

                ),

                child: Text(

                  "Submit",

                  style: TextStyle(

                    fontSize: 24.0,

                  ),

                ),

                onPressed: () => _submit(),

              )

            ],

          ),

        ),

      ),

    );

  }

}