Flutter Age Validator App

main.dart

import 'package:flutter/material.dart';

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

// Hello world with material design
class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        title: 'Age Validator App',
        home: Scaffold(
          appBar: AppBar(
            title: Text("Age Validator"),
          ),
          body: Age()
        )
    );
  }
}

class Age extends StatefulWidget {
  @override
  _AgeState createState() {
    return _AgeState();
  }
}

class _AgeState extends State<Age> {

  String _message = "";
  String _name;
  int _age;

  void nameOnSubmitted(String value) {
    _name = value;
  }

  void ageOnSubmitted(String value) {
    try {
        _age = int.parse(value);
    } on FormatException catch(ex) {
       setState(() {
          _message = "Please enter a valid age";
      });
    }
  }

  void enterClub() {
    setState(() {
      if (_age >= 18) {
        _message = "Hello $_name, You are allowed entry";
      }
      else {
        _message = "Entry denied";
      }
    });
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      padding: EdgeInsets.all(16),
      child: Column(
        children: <Widget>[
          Text(_message, style: TextStyle(fontSize: 20)),
          TextField(
            decoration: InputDecoration(
                hintText: "Name"
            ),
            onChanged: nameOnSubmitted,
          ),
          TextField(
            decoration: InputDecoration(
                hintText: "Age"
            ),
            onChanged: ageOnSubmitted,
          ),
          RaisedButton(
            child: Text("Enter", style: TextStyle(
                fontSize: 20
            ),),
            onPressed: enterClub,
          )
        ],
      ),
    );
  }
}