当运行此代码时，我看到一个白色页面5秒，然后加载页面一会儿，然后是主页。我希望看到加载页面5秒。我认为问题出在加载页面的代码中。有没有办法让我看到加载页面5秒？
main.dart

import 'package:flutter/material.dart';
import 'pages/home.dart';
import 'pages/loading.dart';

void main() {
  runApp(MaterialApp(
      initialRoute: '/loading',
      routes: {
        '/loading': (context) => const Loading(),
        '/home': (context) => const Home(),
        },
    )
  );
}

载入页面

import 'package:flutter/material.dart';
import 'package:flutter/scheduler.dart';

class Loading extends StatefulWidget {
  const Loading({Key? key}) : super(key: key);

  @override
  State<Loading> createState() => _LoadingState();
}

class _LoadingState extends State<Loading> {

  @override
  void initState() {
    super.initState();
  }

  @override
  void didChangeDependencies() {
    super.didChangeDependencies();
    SchedulerBinding.instance.addPostFrameCallback((_) {
      Future.delayed(const Duration(seconds: 5));
      Navigator.pushReplacementNamed(context, '/home');
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.purpleAccent,
      body: SafeArea(child: Container(
          decoration: const BoxDecoration(
            image: DecorationImage(
                image: AssetImage('assets/loadingBackground.JPG'),
                fit: BoxFit.cover),
          ),
      ),
    ),
    );
  }
}