未处理的异常:在flutter中下载文件时，在反按后在dispose()之后调用setState()

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;

class DownloadPage extends StatefulWidget {
  @override
  _DownloadPageState createState() => _DownloadPageState();
}

class _DownloadPageState extends State<DownloadPage> {
  bool _isDisposed = false;

  @override
  void dispose() {
    _isDisposed = true;
    // 取消下载任务
    // cancel download task
    super.dispose();
  }

  void _downloadFile() async {
    // 下载文件逻辑
    // download file logic
    try {
      final response = await http.get('file_url');
      // 下载完成后检查页面是否已销毁
      // check if the page is disposed after download completes
      if (!_isDisposed) {
        setState(() {
          // 更新状态
          // update state
        });
      }
    } catch (e) {
      // 错误处理
      // error handling
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Download Page'),
      ),
      body: Center(
        child: RaisedButton(
          onPressed: _downloadFile,
          child: Text('Download'),
        ),
      ),
    );
  }
}