flutter - 从 Flutter 下载 pdf 时的权限问题

Question

给定权限并创建目录：

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

  void getHttp() async 
  {
    print("Got called");
    requestPersmission();

    Directory appDocDirectory = await getApplicationDocumentsDirectory();
    print(appDocDirectory);

    Directory directory =
        await new Directory(appDocDirectory.path + '/' + 'sulaksh')
            .create(recursive: true);
    print(directory);

    requestPersmission();


    var response =
        await Dio().download('https://www.google.com/', '$directory/xx.html');
  
    print(response);
  }

AndriodManifest.xml：
在这里我放了所需的权限：

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.buttons">

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

    <application .......

重新启动应用程序多次，仍然收到此错误：

E/flutter ( 4223): [ERROR:flutter/lib/ui/ui_dart_state.cc(199)] Unhandled Exception:  
FileSystemException: Creation failed, path = 'Directory: '' (OS Error: Read-only file  
system, errno = 30)