// Look at the stackoverflow link for description...

import 'package:flutter/material.dart';

void main() {
  runApp(new MaterialApp(
    home: new HomePage(),
  ));
}

class HomePage extends StatefulWidget {
  HomePageState createState() => new HomePageState();
}

class HomePageState extends State {

  TextEditingController _controller = new TextEditingController();
  bool _enabled = false;

  @override
  Widget build(BuildContext context) {
    ThemeData theme = Theme.of(context);
    return new Scaffold(
      appBar: new AppBar(
        title: new Text('Disabled Text'),
      ),
      floatingActionButton: new FloatingActionButton(
        child: new Icon(Icons.free_breakfast),
        onPressed: () {
          setState(() {
            _enabled = !_enabled;
          });
        }
      ),
      body: new Center(
        child: new Container(
          margin: const EdgeInsets.all(10.0),
          child: _enabled ?
          new TextFormField(controller: _controller) :
          new FocusScope(
            node: new FocusScopeNode(),
            child: new TextFormField(
              controller: _controller,
              style: theme.textTheme.subhead.copyWith(
                color: theme.disabledColor,
              ),
              decoration: new InputDecoration(
                hintText: _enabled ? 'Type something' : 'You cannot focus me',
              ),
            ),
          ),
        ),
      ),
    );
  }
}