Asynctask and Error Handling on Android

AsyncTask and error handling on Android

It works fine but is it the "right"
approach and is there better
alternative?

I hold onto the Throwable or Exception in the AsyncTask instance itself and then do something with it in onPostExecute(), so my error handling has the option of displaying a dialog on-screen.

How to gracefully handle exception inside AsyncTask in Android?

You can't show dialog in non-ui thread. You can pass activity reference to async task. To handle this situation you can try catch the exception in doInBackground and re-throw it in onPostExecute

e.g.

private class MyAsyncTaskTask extends AsyncTask<...> {

     private Activity ownerActivity;
     private Exception exceptionToBeThrown;

     public MyAsyncTaskTask(Activity activity) {
         // keep activity reference
         this.ownerActivity = activity;
     }

     protected Long doInBackground(...) {
         try {
             ...
         } catch (Exception e) {
             // save exception and re-thrown it then. 
             exceptionToBeThrown = e;
         }
     }

     protected void onPostExecute(...) {
         // Check if exception exists.
         if (exceptionToBeThrown != null) {
             ownerActivity.handleXXX();
             throw exceptionToBeThrown;
         }
     }
 }

If you async task is in Acvitiy class, then you can directly access it, e.g.,

public class MyActivity extends Activity {
    ...
    AsyncTask<...> task = new AsyncTask<...>() {
        public void onPostExecute(...) {
            // Access activity directly
            MyActivity.this.xxx()
        }
    }
}

How to set proper error message on AsyncTask in android studio?

You should create new AsyncTaskResult with passing your exception object, something like this :

AsyncTask<String, String, AsyncTaskResult<JSONObject>> jsonLoader = new AsyncTask<String, String, AsyncTaskResult<JSONObject>>() {

        @Override
        protected AsyncTaskResult<JSONObject> doInBackground(
                String... params) {
            try {
                // get your JSONObject from the server
                return new AsyncTaskResult<JSONObject>(JSon Object);
            } catch (Exception E) {
                return new AsyncTaskResult<JSONObject>(E);
            }
        }

        protected void onPostExecute(AsyncTaskResult<JSONObject> result) {
            if ( result.getError() != null ) {
                // error handling here
            } else {
                JSONObject yourResult = result.getResult();
                // result handling here
            }
        };

    }

Async Task Error Handling

What you can do (I'm using this trick in my app) is this:

protected Object doInBackground(Object... arg0) {
    try {
        prs.setStation(strStation);
        return null;
    }
    catch(Exception ex)
    {
        return ex;
    }
}

protected void onPostExecute(Object result) {
    progDialog.hide();         
    if(result != null && result instanceof Exception) {
        String errText = ((Exception)result).getMessage();
        //now deal with your exception on the UI thread
    }
}

Managing exception in AsyncTask

I got the solution. Maybe, it is not the best one.

I get the lastBackup outside AsyncTask, this way I can declare throws BackupException.

 public void remote(final Backup backup) throws BackupException {
        local(backup);
        final File lastBackup = getLastBackup();
        AsyncTask.execute(new Runnable() {
            @Override
            public void run() {
                BackupSendInfo sendInfo = new BackupSendInfo()
                        .setFile(lastBackup)
                        .setFileName(getBackupName(backup))
                        .setBackup(backup)
                        .setDeviceId("Desconocido") //TODO leer dispositivo del fichero deviceName
                        .setApp(config.getAppName());
                fileSender.send(sendInfo);
            }
        });
    }

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