Flutter: Buttons inside ListView. Button onPressed will change the color of the button

main.dart

import 'package:flutter/material.dart';

void main() => runApp(
  new MaterialApp(home: new MyApp())
);

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => new _MyAppState();
}

class _MyAppState extends State<MyApp> {
  static var btnPressed;

  void onPressed(btnNumber){
    setState(() {
      btnPressed = btnNumber;
    });
  }
   Widget createButton(btnName) {
     var clr = Colors.blue;
     if(btnPressed != null && btnPressed == btnName) {
       clr = Colors.yellow;
     }
     Widget btn = new FlatButton(
        color: clr,
        disabledColor: Colors.grey,
        child: new Text(btnName, style: new TextStyle(fontSize: 20.0),),
        onPressed: () => onPressed(btnName),
      );
      return btn;
   }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      body: new Center(
        child: new Container(
          alignment: Alignment.center,
          height: 100.0,
          //width: 200.0,
          padding: const EdgeInsets.all(10.0),
          child: new ListView(
            scrollDirection: Axis.horizontal,
            children: <Widget>[
              createButton('b1'),
              new Padding(padding: const EdgeInsets.only(right: 10.0),),
              createButton('b2'),
              new Padding(padding: const EdgeInsets.only(right: 10.0),),
              createButton('b3'),
              new Padding(padding: const EdgeInsets.only(right: 10.0),),
              createButton('b4'),
              new Padding(padding: const EdgeInsets.only(right: 10.0),),
              createButton('b5'),
            ],
          ),
        ),
      ),
    );
  }
}