如何在flutter中制作这样的自定义应用栏？

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: PreferredSize(
          preferredSize: Size.fromHeight(60.0),
          child: AppBar(
            title: Text(
              'Custom App Bar',
              style: TextStyle(
                fontSize: 20.0,
                fontWeight: FontWeight.bold,
              ),
            ),
            actions: [
              IconButton(
                icon: Icon(Icons.search),
                onPressed: () {
                  // Add your search functionality here
                },
              ),
              IconButton(
                icon: Icon(Icons.notifications),
                onPressed: () {
                  // Add your notification functionality here
                },
              ),
            ],
            leading: IconButton(
              icon: Icon(Icons.menu),
              onPressed: () {
                // Add your menu functionality here
              },
            ),
            flexibleSpace: Container(
              decoration: BoxDecoration(
                gradient: LinearGradient(
                  colors: [Colors.blue, Colors.green],
                  begin: Alignment.topLeft,
                  end: Alignment.bottomRight,
                ),
              ),
            ),
          ),
        ),
        body: Center(
          child: Text('Custom App Bar Example'),
        ),
      ),
    );
  }
}