Form example with saved and validation

main.dart

import 'package:flutter/material.dart';

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

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

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  final _formKey = GlobalKey<FormState>();
  String _inputMessage = '';

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Container(
        padding: EdgeInsets.all(10),
        child: Form(
          key: _formKey,
          child: Column(
            mainAxisAlignment: MainAxisAlignment.start,
            crossAxisAlignment: CrossAxisAlignment.start,
            children: <Widget>[
              Text('ข้อความ'),
              SizedBox(
                height: 10,
              ),
              TextFormField(
                onSaved: (value) {
                  _inputMessage = value;
                },
                validator: (value) {
                  if (value == null) {
                    return "กรุณากรอกข้อความ";
                  } else {
                    return "";
                  }
                },
              ),
              SizedBox(
                height: 10,
              ),
              SizedBox(
                width: double.infinity,
                child: RaisedButton(
                  onPressed: () {
                    if (_formKey.currentState.validate()) {
                      _formKey.currentState.save();
                      print(_inputMessage);
                    }
                  },
                  child: Text('Submit'),
                ),
              )
            ],
          ),
        ),
      ),
    );
  }
}