Material changing

main.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  final _controller = new TextEditingController();
  bool _showController = false;
  Color _color = Colors.red;

  void _toggleController() {
    setState(() {
      _showController = !_showController;
    });
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      body: new Center(
        child: new Container(
          width: 200.0,
          height: 200.0,
          child: new Material(
            shadowColor: _color,
            elevation: 8.0,
            child: _showController ? new TextField(controller: _controller) : new Container(),
          ),
        ),
      ),
      floatingActionButton: new FloatingActionButton(
        onPressed: _toggleController,
        tooltip: 'Increment',
        child: new Icon(Icons.add),
      ),
    );
  }
}