android - 从 url 下载 PDF 文件并存储在内部存储中，然后尝试从任何 PDF 阅读器打开它，它显示的文件格式在 flutter 中不受支持

Question

我试图在我的应用程序中打开我下载的 PDF 文件，然后它显示正常，但是当我从任何其他应用程序(如 PDF 阅读器)打开它时，它显示的文件格式不受支持。

• PDF文件存放在这个目录:
  内部存储/MyApp/pdf
• 我想从任何 PDF 阅读器访问该 PDF 文件或从我的文件管理器打开它，所以需要做什么。
• 我没有使用 getExternalStorageDirectory() 的路径目录
• 我直接给内部存储路径，比如/storage/emulated/0/MyApp

这是我的完整代码

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

void main(){
  runApp(new MaterialApp(
      debugShowCheckedModeBanner: false,
      home: new FileDownloadView()

  ));
}


class FileDownloadView extends StatefulWidget {
  @override
  _FileDownloadViewState createState() => _FileDownloadViewState();
}

class _FileDownloadViewState extends State<FileDownloadView> {
  String _filePath = "";

  Future<String> get _localDevicePath async {

    final _devicePath = await getExternalStorageDirectory();
    return _devicePath.path;
  }

  Future<File> _localFile({String path, String type}) async {
    String _path = await _localDevicePath;

    var _newPath = await Directory("/storage/emulated/0/$path").create();
    return File("${_newPath.path}/pdf.$type");
  }

  Future _downloadSamplePDF() async {
    final _response =
    await http.get("https://firebasestorage.googleapis.com/v0/b/text-recognition-28371.appspot.com/o/Direct%20Recruitment%202020.pdf?alt=media&token=114498c1-0e84-48e0-bda0-15d4b688f745");
    if (_response.statusCode == 200) {
      final _file = await _localFile(path: "MyApp", type: "pdf");
      final _saveFile = await _file.writeAsBytes(_response.bodyBytes);

      Logger().i("File write complete. File Path ${_saveFile.path}");
      setState(() {
        _filePath = _saveFile.path;
      });
    } else {
      Logger().e(_response.statusCode);
    }
  }

  Future _downloadSampleVideo() async {
    final _response = await http.get(
        "https://sample-videos.com/video123/mp4/720/big_buck_bunny_720p_2mb.mp4");
    if (_response.statusCode == 200) {
      final _file = await _localFile(type: "mp4", path: "videos");
      final _saveFile = await _file.writeAsBytes(_response.bodyBytes);
      Logger().i("File write complete. File Path ${_saveFile.path}");
      setState(() {
        _filePath = _saveFile.path;
      });
    } else {
      Logger().e(_response.statusCode);
    }
  }


  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            FlatButton.icon(
              icon: Icon(Icons.file_download),
              label: Text("Sample Pdf"),
              onPressed: () {
                _downloadSamplePDF();



              },
            ),
            FlatButton.icon(
              icon: Icon(Icons.file_download),
              label: Text("Sample Videos"),
              onPressed: () {
                _downloadSampleVideo();

              },
            ),
            Text(_filePath),
            FlatButton.icon(
              icon: Icon(Icons.shop_two),
              label: Text("Show"),
              onPressed: () async {
                final _openFile = await OpenFile.open(_filePath);
                Logger().i(_openFile);
              },
            ),
          ],
        ),
      ),
    );
  }
}

Android list

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example2.downloder_app">
    <uses-permission android:name="android.permission.INTERNET"></uses-permission>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"></uses-permission>
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"></uses-permission>
    <uses-permission android:name="android.permission.READ_PHONE_STATE"></uses-permission>
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <!-- io.flutter.app.FlutterApplication is an android.app.Application that
         calls FlutterMain.startInitialization(this); in its onCreate method.
         In most cases, you can leave this as-is, but you if you want to provide
         additional functionality it is fine to subclass or reimplement
         FlutterApplication and put your custom class here. -->
    <application
        android:name="io.flutter.app.FlutterApplication"
        android:label="downloder_app"
        android:icon="@mipmap/ic_launcher"
        android:testOnly="false">
        <activity
            android:name=".MainActivity"
            android:launchMode="singleTop"
            android:theme="@style/LaunchTheme"
            android:configChanges="orientation|keyboardHidden|keyboard|screenSize|smallestScreenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
            android:hardwareAccelerated="true"
            android:windowSoftInputMode="adjustResize">
            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>
                <category android:name="android.intent.category.LAUNCHER"/>
            </intent-filter>
        </activity>
        <!-- Don't delete the meta-data below.
             This is used by the Flutter tool to generate GeneratedPluginRegistrant.java -->
        <meta-data
            android:name="flutterEmbedding"
            android:value="2" />
    </application>
</manifest>

Answer 1

您可能需要添加 permission_handler在您的工作流程中启用对设备存储的写入权限。

您是否能够验证下载的文件是否确实写入了存储？如果文件已下载但有 0 个字节，则可能存在问题。

我建议避免硬编码根路径，因为它可能会根据您使用的平台版本而改变。相反，您可以考虑使用 getApplicationDocumentsDirectory() - 这应该将文件写入 app 目录。如果数据需要对用户可见，可以使用getExternalStorageDirectory()适用于 Android。