android - java.io.FileNotFoundException : Permission denied - in flutter i got this error

  Future<File> getFileFromUrl(String url, {name}) async {
    var fileName = 'testonline';
    if (name != null) {
      fileName = name;
    }
    try {
      var data = await http.get(url);
      var bytes = data.bodyBytes;
      var dir = await getApplicationDocumentsDirectory();
      File file = File("${dir.path}/" + fileName + ".pdf");
      File urlFile = await file.writeAsBytes(bytes);
      return urlFile;
    } catch (e) {
      throw Exception("Error opening url file");
    }
  }

这是我的示例代码，用于将文件保存在应用程序目录中并在以后使用。

最佳答案

您可以在下面复制粘贴运行完整代码
您需要请求WRITE_EXTERNAL_STORAGE权限
您可以在工作演示中看到文件下载成功

步骤1:将WRITE_EXTERNAL_STORAGE添加到AndroidManifest.xml

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

步骤2:将permission_handler: 4.4.0添加到pubspec.yaml

dependencies:
  flutter:
    sdk: flutter
  http: any
  path_provider: any
  permission_handler: 4.4.0

步骤3:请求存储权限

void requestPersmission() async {
    await PermissionHandler().requestPermissions([PermissionGroup.storage]);
  }

  @override
  void initState() {
    requestPersmission();
    super.initState();
  }

工作演示



完整的代码

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

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: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  Future<File> getFileFromUrl(String url, {name}) async {
    var fileName = 'testonline';
    if (name != null) {
      fileName = name;
    }
    try {
      var data = await http.get(url);
      var bytes = data.bodyBytes;
      var dir = await getApplicationDocumentsDirectory();
      File file = File("${dir.path}/" + fileName + ".pdf");
      print(dir.path);
      File urlFile = await file.writeAsBytes(bytes);
      return urlFile;
    } catch (e) {
      throw Exception("Error opening url file");
    }
  }

  void _incrementCounter() {
    getFileFromUrl("http://www.africau.edu/images/default/sample.pdf");
    setState(() {
      _counter++;
    });
  }

  void requestPersmission() async {
    await PermissionHandler().requestPermissions([PermissionGroup.storage]);
  }

  @override
  void initState() {
    requestPersmission();
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headline4,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}