Handling exceptions in AsyncTask.doInBackground in an Activity?

Question

I am following the guide on Processes and Threads to implement an AsyncTask in an android activity in which I will perform some database access. However, my code has to handle an exception in doInBackground .

My current thinking is to provide a Toast popup to inform the user of this exception, but now I am afraid this too " violates the second rule of the single-threaded model: do not access the Android UI toolkit from outside the UI thread " (as per the guide).

Would I be wrong in providing a Toast popup? Is there a better way to handle exceptions in the doInBackground method?

Answer 1

Will the exception cause you to stop what doInBackground is processing?

If yes, store what exception you encountered, exit doInBackground and show the Toast in onPostExecute

If no, pass the exception information to onProgressUpdate with publishProgress .

Trying to pop-up the Toast in doInBackground will not work.

Answer 2

You can use runOnUIThread to update UI from background thread

  @Override
  protected void doInBackground(Void... params) {
   try{
        // do some stuff
    }catch(Exception ex){
    ex.printStackTrace();
    final String message = ex.getMessage();
        yourActivity.runOnUiThread(new Runnable() {
            public void run() {
               // show toast
                Toast.makeText(getApplicationContext, message, Toast.LENGTH_SHORT).show();
            }
        });
    }

}