title: File.list and File.listFiles return NULL
body: <p>in my app, the user can download different sound files. I use the downloadManager for this and everything is working fine here.</p>
  
  <pre><code>String url = localList.get(position).guid;
  DownloadManager.Request request = new DownloadManager.Request(Uri.parse(url));
  request.setDescription(localList.get(position).title);
  request.setTitle("Downloading Podcast");
  
  if (Build.VERSION.SDK_INT &gt;= Build.VERSION_CODES.HONEYCOMB) {
      request.setNotificationVisibility(DownloadManager.Request.
      VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
  }
  
  
  request.setDestinationInExternalPublicDir("/MyAudio/",
  localList.get(position).title + ".mp3");
  
  DownloadManager manager = (DownloadManager)
  v.getContext().getSystemService(Context.DOWNLOAD_SERVICE);
  manager.enqueue(request);
  </code></pre>
  
  <p>The problem is, when i try to show all files in the directory with file.list or file.listfiles its returning NULL.</p>
  
  <pre><code>File f = new File("/MyAudio/");
  File file[] = f.listFiles();
  String filename[] = f.list();
  </code></pre>
  
  <p>I tried a lot of stuff, like changing the folder name and location, using request.setDestinationInExternalFileDir , writing and reading the folder with</p>
  
  <pre><code>File sdCard = Environment.getExternalStorageDirectory();
  String folder = sdCard.getAbsolutePath() + "/MyAudio" ;
  </code></pre>
  
  <p>But nothing helped so far. I always get NULL returned by file.listFiles.</p>
  
  <p>I use these permissions:</p>
  
  <pre><code>&lt;uses-permission android:name="android.permission.INTERNET" /&gt;
  &lt;uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /&gt;
  &lt;uses-permission android:name="android.permission.ACCESS_WIFI_STATE" /&gt;
  &lt;uses-permission android:name="android.permission.CHANGE_WIFI_STATE" /&gt;
  &lt;uses-permission android:name="android.permission.INTERNET" /&gt;
  &lt;uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" /&gt;
  &lt;uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" /&gt;
  </code></pre>
  
  <p>which should cover everything i need. </p>
  
  <p>One last point: I write the file in an arrayadapter class and try to read the folder from my mainactivity, and i see the folder and files on my phone, so im sure they exist.</p>
  
  <p>Thx in advance</p>