java - setDestinationInExternalFilesDir() 有效 setDestinationInExternalPublicDir() 无效

Question

我正在尝试从 url 下载文件并将其保存到常规下载文件夹。 setDestinationInExternalPublicDir() 不起作用，也不会引发任何异常。但是 setDestinationInExternalFilesDir() 工作正常。知道原因是什么吗？

我的代码是这样的:

webView.setDownloadListener(new DownloadListener() {
    @Override
    public void onDownloadStart(String url, String userAgent,
                                String contentDisposition, String mimeType,
                                long contentLength) {

        if (url.startsWith("data:")) {
            save(url);
            return;
        }


        DownloadManager.Request request = new DownloadManager.Request(Uri.parse(url));
        request.setMimeType(mimeType);
        String cookies = CookieManager.getInstance().getCookie(url);
        request.addRequestHeader("cookie", cookies);
        request.addRequestHeader("User-Agent", userAgent);
        request.setDescription(getResources().getString(R.string.downloadingMsg));
        String filename = URLUtil.guessFileName(url, contentDisposition, mimeType);
        request.setTitle(filename);
        request.allowScanningByMediaScanner();
        request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
//DOESN'T WORK
            request.setDestinationInExternalPublicDir("Downloads", filename); 
//WORKS
            //request.setDestinationInExternalFilesDir(getApplicationContext(), "Downloads", filename); 
        DownloadManager dm = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);
        dm.enqueue(request);
        Toast.makeText(getApplicationContext(), R.string.downloadingMsg, Toast.LENGTH_LONG).show();
    }
});

和 list 文件:

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

Answer 1

所以，我终于可以让 setDestinationInExternalPublicDir() 函数工作了。感谢 CommonsWare。通过关注 Commonsware 的评论和回答 here我了解到，在 Android 版本 6+ 上，即使 list 文件中声明了权限，仍然应该在运行时请求它们。你猜怎么着，我正在使用 android 7...也就是说，我收到了权限被拒绝错误。

因此，我在 onCreate() 函数中添加了这些行，该函数也会提示用户获得运行时的权限(最终解决了我的问题):

    if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.M) {
        int PERMISSION_REQUEST_CODE = 1;
        if (ContextCompat.checkSelfPermission(MainActivity.this,
                Manifest.permission.WRITE_EXTERNAL_STORAGE)
                != PackageManager.PERMISSION_GRANTED) {

            if (ActivityCompat.shouldShowRequestPermissionRationale(MainActivity.this,
                    Manifest.permission.WRITE_EXTERNAL_STORAGE)) {
            } else {
                ActivityCompat.requestPermissions(MainActivity.this,
                        new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},
                        PERMISSION_REQUEST_CODE);
            }
        }
    }