AsyncTask called from Handler will not execute doInBackground

The application I'm working on is using a background thread to download a list of images through a API, then display the images in a slideshow. There is a background task (currently AsyncTask) to periodically fetch the new images. I'm not getting any error messages about the wrong Thread etc, it's just that the AsyncTasks's second instance will not run the doInBackground method. Here is some code from the Activity: ``` private DownloadTask mDownloadTask = null; private Handler mHandler; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); mHandler = new Handler() { @Override public void handleMessage(Message msg) { if(mDownloadTask != null) { mDownloadTask.cancel(true); } mDownloadTask = new DownloadTask(); mDownloadTask.execute((Void[]) null); } }; mDownloadTask = new DownloadTask(); mDownloadTask.execute((Void[]) null); } ``` The `DownloadTask` looks like this: ``` @Override protected List<String> doInBackground(Void... voids) { // Download list of URLs from server, etc. } @Override protected void onPostExecute(List<String> urls) { mHandler.sendEmptyMessageDelayed(111, 5000); } ``` The handler will be called, the onPreExecute (in the AsyncTask) will be called and the initial run of DownloadTask (right in `onCreate`) also works. According to this question: Android SDK AsyncTask doInBackground not running (subclass) , it might be SDK15 related. Thanks for any hints. Update As I received comments that the Handler might not be in the UI thread (which is weird, as `Thread.currentThread` is the same both in onCreate and the Handlers `handleMessage` method, I revised the `handleMessage` method to: ``` mHandler = new Handler() { @Override public void handleMessage(Message msg) { runOnUiThread(new Runnable() { @Override public void run() { if(mDownloadTask != null) { mDownloadTask.cancel(true); } mDownloadTask = new DownloadTask(); mDownloadTask.execute((Void[]) null); } }); } }; ``` Still without success. Update the full DownloadTask class ``` class DownloadTask extends AsyncTask<Void, Void, List<String>> { @Override protected void onPreExecute() { // Cancel the animation. if (mSlideshowAnimation != null) { mSlideshowAnimation.cancel(true); } mImageView1.setVisibility(View.GONE); mImageView2.setVisibility(View.GONE); animate(mProgressBar).alpha(1.0f).setDuration(500).start(); Log.d(TAG, "Download preparation done."); } @Override protected List<String> doInBackground(Void... voids) { Log.d(TAG, "Download"); SharedPreferences s = getSharedPreferences("access", Context.MODE_PRIVATE); String token = s.getString("token", null); Log.d(TAG, "Downloading slideshows."); List<String> urls = new ArrayList<String>(); Slideshow[] slideshows = new Api(SlideshowActivity.this).getSlideshows(token); for (Slideshow slideshow : slideshows) { urls.addAll(slideshow.getAllPhotoUrls()); } Log.d(TAG, "Downloading slideshows: " + slideshows.length); for (String url : urls) { try { url = Api.HOST + url; if (!Cache.fileExists(Cache.getCacheFilenameForUrl(SlideshowActivity.this, url))) { Cache.cacheStream(SlideshowActivity.this, HttpHelper.download(SlideshowActivity.this, url), url); } else { Log.d(TAG, "Cached: " + url); } } catch (IOException e) { Log.e(TAG, "Error while downloading.", e); } } Log.d(TAG, "Downloading slideshows finished."); return urls; } @Override protected void onPostExecute(List<String> urls) { Log.d(TAG, "download successful"); animate(mProgressBar).alpha(0.0f).setDuration(500).start(); mCurrentImageIndex = -1; mImageUrls = urls; mSlideshowAnimation = new SlideshowAnimation(); mSlideshowAnimation.execute((Void[]) null); mHandler.sendEmptyMessageDelayed(111, 5000); } } ```