Retrieve file path from caught DownloadManager intent

问题

Since Android 4.2 if a user downloads some file in the browser the DownloadManager is used. If the user clicks the 'download complete' notification an Intent is and was always launched. Before Android 4.2 the intent used to have the downloaded file's path in the content, such that:

intent.getData()

would return a String such as file:///storage/emulated/0/Download/some_file.ext. However, since Android 4.2 the download manager broadcasts and intent with a content scheme, such as content://downloads/all_downloads/2334.

How do I retrieve the local file path for a downloaded file?

I've tried the following:

public static String getRealPathFromURI(Uri contentUri, Activity activity) {
    DownloadManager downloadManager = (DownloadManager) activity.getSystemService(Activity.DOWNLOAD_SERVICE);
    String[] contentParts = contentUri.getEncodedPath().split("/");
    Cursor q = downloadManager.query(new DownloadManager.Query().setFilterById(Integer.parseInt(contentParts[contentParts.length - 1])));
    if (q == null) {
        // Download no longer exists
        return null;
    }
    q.moveToFirst();
    return q.getString(q.getColumnIndex(DownloadManager.COLUMN_LOCAL_FILENAME));
}

But the cursor never returns any rows (so q.getCount() == 0 and therefor the last return statement throws an exception). Also, the hack by parsing the download file id from the Uri seems odd.

UPDATE: I have also tried:

input = getActivity().getContentResolver().openInputStream(contentUri);

but this returns an error stating

Permission Denial: reading com.android.providers.downloads.DownloadProvider uri content://downloads/all_downloads/2334 from pid=30950, uid=10064 requires android.permission.ACCESS_ALL_DOWNLOADS, or grantUriPermission()

Clearly I can't access the downloads (as my app did not initiate them - the browser did) through the ContentProvider.

回答1:

Getting it through the content resolver is the right thing. Not every content url is going to be a file. For example, the Gallery app will give you uri's that translate to a network call or a local file depending on the source.

Even if you'd get to the real file path, you'll probably unable to read it, due to file permissions, although you can be lucky it it's on external storage. Have you tried adding android.permission.ACCESS_ALL_DOWNLOADS to your app like the exception suggests? That won't work, since the permission is at signature level :(

回答2:

Here's what worked. First, you can't (and shouldn't want to) get the file path as botteaap correctly pointed out. (Credits to him for setting me on the right path.) Instead you get a temporary permission automatically to access the file content, using:

InputStream input = getContentResolver().openInputStream(intent.getData());

You can read this InputStream like any other in Java. It seems there is no way to get the file name. If you need a file, first write the input stream to a (temporary) file.

The SecurityException is throw when your temporary access was revoked. This happend for me on some files that I tried to read incorrectly before and specifically when the Intent was picked up in my Acticity's onNewIntent.

回答3:

I just want to add to the answer from @erickok as it took me several hours to figure this out. As stated by @jcesarmobile, you are only guaranteed to be able to get the name and size of the file, not the full path.

You can get the name and size as follows, and then save to a temp file:

String filename = null;
Long filesize = null;
Cursor cursor = null;
try {
    cursor = this.getContentResolver().query(intent.getData(), new String[] {
        OpenableColumns.DISPLAY_NAME, OpenableColumns.SIZE}, null, null, null );
    if (cursor != null && cursor.moveToFirst()) {
        filename = cursor.getString(0);
        filesize = cursor.getLong(1);
    }
} finally {
    if (cursor != null)
        cursor.close();
}

来源：https://stackoverflow.com/questions/14364091/retrieve-file-path-from-caught-downloadmanager-intent