Question

你好朋友，我在用户安装我的应用程序时创建项目，他们首先从互联网下载zip文件并提取其中的所有文件，然后在我的应用程序中显示，但是问题是当用户下载并提取文件时，zip图像在应用程序中显示时，我关闭了应用程序，然后重新打开它，每次他们需要单击下载按钮时都没有从文档目录中加载图片，然后在应用程序中显示该图片。有人告诉我这里的问题是代码吗？

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(),
          ],
        ),
      ),
    );
  }
}

Answer 1

您可以在下面复制粘贴运行完整代码
您可以使用软件包List<String>保存和恢复SharedPreferences
代码段

getHistoryImageList() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    setState(() {
      _images = prefs.getStringList("images");
    });
  }
...
Future<void> _downloadZip() async {
    ...
    await unarchiveAndSave(zippedFile);

    SharedPreferences prefs = await SharedPreferences.getInstance();
    prefs.setStringList("images", _tempImages);
    setState(() {
      _images = List<String>.from(_tempImages);
      _downloading = false;
    });
  }

工作演示

完整代码

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';
import 'package:shared_preferences/shared_preferences.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';

  getHistoryImageList() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    setState(() {
      _images = prefs.getStringList("images");
    });
  }

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

  _initDir() async {
    if (null == _dir) {
      _dir = (await getApplicationDocumentsDirectory()).path;
      print("init $_dir");
    }
  }

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

    SharedPreferences prefs = await SharedPreferences.getInstance();
    prefs.setStringList("images", _tempImages);
    setState(() {
      _images = List<String>.from(_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}';
      print("fileName ${fileName}");
      if (file.isFile && !fileName.contains("__MACOSX")) {
        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 _images == null
        ? Container()
        : 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(),
          ],
        ),
      ),
    );
  }
}

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: DownloadAssetsDemo(),
    );
  }
}

下载ZIP，解压缩并显示图像文件，但无法从文档目录加载？

1 个答案: