在flutter中，当后退按钮被按下时，我如何返回到上一个URL？

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('Flutter Back Button'),
        ),
        body: Center(
          child: RaisedButton(
            child: Text('Go to Second Page'),
            onPressed: () {
              Navigator.push(
                context,
                MaterialPageRoute(builder: (context) => SecondPage()),
              );
            },
          ),
        ),
      ),
    );
  }
}

class SecondPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Second Page'),
      ),
      body: Center(
        child: RaisedButton(
          child: Text('Go Back'),
          onPressed: () {
            Navigator.pop(context);
          },
        ),
      ),
    );
  }
}