_MyHomePageState.dart

_MyHomePageState.dart

import ...
import 'package:flutter_mqtt/thermometer_widget.dart';

...

class _MyHomePageState extends State<MyHomePage> {
 ...

 @override
 Widget build(BuildContext context) {
   return Scaffold(
     appBar: AppBar(
       title: Text(widget.title),
     ),
     body: Center(
       child: SizedBox(
         child: ThermometerWidget(
           borderColor: Colors.red,
           innerColor: Colors.green,
           indicatorColor: Colors.red,
           temperature: _temp,
         ),
       ),
     ),
     floatingActionButton: FloatingActionButton(
       onPressed: _connect,
       tooltip: 'Play',
       child: Icon(Icons.play_arrow),
     ), 
   );
 }