Check if file downloaded with DownloadManager still exist on device storage

Question

I'm downloading all files in my application using DownloadManager. Also, I save all id's which enqueue method returns. The question is: How to determine is file still exist after some amount of time?

I'm trying to do this in that way

Cursor c =
        mgr.query(new DownloadManager.Query().setFilterById(lastDownload));

if (c == null || !c.moveToFirst()) {
    // File doesn't exist?
}

But that didn't work. Sometimes downloadManager returns a Cursor and moveToFirst invocation return true but in fact, downloaded file was been deleted from a filesystem.

Okay, second way I found - obtain a content Uri from the download manager. Also, I'm reading this post about content Uri limitations. If I understand correctly, in short - Uri doesn't guarantee that content exists, furthermore, Uri even doesn't guarantee that content IS A file. Anyway, I think that this construction should work:

try {
    contentResolver.openFileDescriptor(contentUri, "r");
} catch (FileNotFoundException e) {
    // File doesn't exist?
}

But the result is very frustrating. Sometimes (absolutely random) application crash with SecurityException.

java.lang.SecurityException: Permission Denial: reading com.android.providers.downloads.DownloadProvider uri content://downloads/all_downloads/1145 from pid=16585, uid=10086 requires android.permission.ACCESS_ALL_DOWNLOADS, or grantUriPermission()

My questions are: How I can check if downloaded file exists? Why application crashes sometimes? It's looks like heisenbug because behavior is absolutely random.

Answer 1

Have you add permission on your manifest for read or write file.

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

or if you are working on version 23 then you should use security permission condition before fetching data.