How to solve Unhandled Exception: FormatException: Could not find End of Central Directory Record while downloading file in Flutter?

user_10764147 0
Viewed 908

In my Flutter project, I want to download some files as zip and then unzip it programmatically and save it in device locally. So, for that reason I followed some examples, here's the code for that-

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

class DownloadAssetsDemo extends StatefulWidget {
  DownloadAssetsDemo() : super();

  final String title = "Download & Extract ZIP Demo";

  @override
  DownloadAssetsDemoState createState() => DownloadAssetsDemoState();
}

class DownloadAssetsDemoState extends State<DownloadAssetsDemo> {
  //
  bool _downloading;
  String _dir;
  List<String> _images, _tempImages;
  String _zipPath = 'https://coderzheaven.com/youtube_flutter/images.zip';
  String _localZipFileName = 'images.zip';

  @override
  void initState() {
    super.initState();
    _images = List();
    _tempImages = List();
    _downloading = false;
    _initDir();
  }

  _initDir() async {
    if (null == _dir) {
      _dir = (await getApplicationDocumentsDirectory()).path;
    }
  }

  Future<File> _downloadFile(String url, String fileName) async {
    var req = await http.Client().get(Uri.parse(url));
    var file = File('$_dir/$fileName');
    return file.writeAsBytes(req.bodyBytes);
  }

  Future<void> _downloadZip() async {
    setState(() {
      _downloading = true;
    });

    _images.clear();
    _tempImages.clear();

    var zippedFile = await _downloadFile(_zipPath, _localZipFileName);
    await unarchiveAndSave(zippedFile);

    setState(() {
      _images.addAll(_tempImages);
      _downloading = false;
    });
  }

  unarchiveAndSave(var zippedFile) async {
    var bytes = zippedFile.readAsBytesSync();
    var archive = ZipDecoder().decodeBytes(bytes);
    for (var file in archive) {
      var fileName = '$_dir/${file.name}';
      if (file.isFile) {
        var outFile = File(fileName);
        //print('File:: ' + outFile.path);
        _tempImages.add(outFile.path);
        outFile = await outFile.create(recursive: true);
        await outFile.writeAsBytes(file.content);
      }
    }
  }

  buildList() {
    return Expanded(
      child: ListView.builder(
        itemCount: _images.length,
        itemBuilder: (BuildContext context, int index) {
          return Image.file(
            File(_images[index]),
            fit: BoxFit.fitWidth,
          );
        },
      ),
    );
  }

  progress() {
    return Container(
      width: 25,
      height: 25,
      padding: EdgeInsets.fromLTRB(0.0, 20.0, 10.0, 20.0),
      child: CircularProgressIndicator(
        strokeWidth: 3.0,
        valueColor: AlwaysStoppedAnimation<Color>(Colors.white),
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
        actions: <Widget>[
          _downloading ? progress() : Container(),
          IconButton(
            icon: Icon(Icons.file_download),
            onPressed: () {
              _downloadZip();
            },
          ),
        ],
      ),
      body: Container(
        child: Column(
          children: <Widget>[
            buildList(),
          ],
        ),
      ),
    );
  }
}

This example, works fine with all the functionalities- zip file download, extract the file and load the images.

But the problem is

When I want to download the file from my desired location where I have saved a sqlite database(Size:19 mb) as a zip file, it doesn't work like the way it happened for the given code.

It shows the following error exception-

[ERROR:flutter/lib/ui/ui_dart_state.cc(186)] Unhandled Exception: FormatException: Could not find End of Central Directory Record

And I am not exactly getting whether the problem is in my download path or I need to make some changes in my coding example?

So, I need some suggestion to fix this exception and download and unzip my desired file from desired url.

dart flutter download
1 Answers

This was likely caused by the fact that the file was not yet flushed to the filesystem after downloading before attempting to extract same. To fix this update the _downloadFile method to the following

Future<File> _downloadFile(String url, String fileName) async {
    var req = await http.Client().get(Uri.parse(url));
    var file = File('$_dir/$fileName');
    return file.writeAsBytes(req.bodyBytes, flush: true); // Added flush: true
  }

From dart:io docs

Future<File> writeAsBytes(List<int> bytes, {FileMode mode = FileMode.write, bool flush = false})

Writes a list of bytes to a file.

Opens the file, writes the list of bytes to it, and closes the file. Returns a Future<File> that completes with this [File] object once the entire operation has completed.

By default [writeAsBytes] creates the file for writing and truncates the file if it already exists. In order to append the bytes to an existing file, pass [FileMode.append] as the optional mode parameter.

Note: --> If the argument [flush] is set to true, the data written will be flushed to the file system before the returned future completes.
user_53727840
Related