如何使用SelectableDayPredicate将我的DatePicker限制为仅限工作日？

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('Workday DatePicker'),
        ),
        body: Center(
          child: ElevatedButton(
            child: Text('Open DatePicker'),
            onPressed: () {
              _selectDate(context);
            },
          ),
        ),
      ),
    );
  }

  Future<void> _selectDate(BuildContext context) async {
    final DateTime? picked = await showDatePicker(
      context: context,
      initialDate: DateTime.now(),
      firstDate: DateTime(2022),
      lastDate: DateTime(2023),
      selectableDayPredicate: _isWorkday,
    );

    if (picked != null) {
      print('Selected date: $picked');
    }
  }

  bool _isWorkday(DateTime day) {
    // 判断日期是否为工作日
    return day.weekday != DateTime.saturday && day.weekday != DateTime.sunday;
  }
}