如何在RawMaterialButton中使用onLongPressed属性连续增加或减少一个值？

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: MyHomePage(),
    );
  }
}

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

class _MyHomePageState extends State<MyHomePage> {
  int count = 0;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('RawMaterialButton Example'),
      ),
      body: Center(
        child: RawMaterialButton(
          onPressed: () {},
          onLongPress: () {
            setState(() {
              count++;
            });
          },
          child: Text(
            'Count: $count',
            style: TextStyle(fontSize: 20),
          ),
          fillColor: Colors.blue,
          padding: EdgeInsets.all(20),
          shape: CircleBorder(),
        ),
      ),
    );
  }
}