使用Android DownloadManager在Android Oreo 8.1中无法成功下载到外部SD卡

Question

我已经编写了一些代码，可以使用Android DownloadManager将文件下载到外部SD卡。在Android 6.0.1（API级别23）上，一切都可以正常工作，但是在Android Oreo（API级别27）上，尽管授予了所有权限，但下载失败并显示“下载失败”。 PermissionUri是使用Intent.ACTION_OPEN_DOCUMENT_TREE（“ / storage / 2633-FECD”）选择的sd卡的Uri。

public static Uri permissionUri;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    SharedPreferences pref = getApplicationContext().getSharedPreferences("AppPrefs", 0);
    String sdUriString = pref.getString("sdUri", null);
    if(sdUriString==null){
        startActivityForResult(new Intent(Intent.ACTION_OPEN_DOCUMENT_TREE), 732);
    }
    else{
        permissionUri = Uri.parse(sdUriString);
    }

    final Button DownloadButton = (Button) findViewById(R.id.downloadButton);
    DownloadButton.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
            DownloadManager dm = (DownloadManager) v.getContext().getSystemService(DOWNLOAD_SERVICE);
            Long downloadID = dm.enqueue(new DownloadManager.Request(Uri.parse("https://www.google.de/images/branding/googlelogo/1x/googlelogo_color_272x92dp.png"))
                    .setAllowedOverRoaming(false)
                    .setTitle("Download")
                    .setDestinationUri(Uri.fromFile(new File("/storage/2633-FECD/Test.jpg")))
                    .setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED)
            );
        }
    });

}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if(requestCode == 732){
        if(resultCode == RESULT_OK){
            permissionUri = data.getData();
            try {
                grantUriPermission(getPackageName(), permissionUri, Intent.FLAG_GRANT_READ_URI_PERMISSION | Intent.FLAG_GRANT_WRITE_URI_PERMISSION);
                getContentResolver().takePersistableUriPermission(permissionUri, Intent.FLAG_GRANT_READ_URI_PERMISSION | Intent.FLAG_GRANT_WRITE_URI_PERMISSION);
                SharedPreferences settings = getSharedPreferences("AppPrefs", MODE_PRIVATE);
                settings.edit().putString("sdUri", permissionUri.toString()).apply();
            }
            catch (Exception e){
            }
        }
    }
}



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