How to handle AsyncTask failure

Question

Is there a specific way to handle failure in an AsyncTask? As far as I can tell the only way is with the return value of task. I\'d like to be able to provide more details o

Answer 1

What I always do is create a new Object (you can call it AsyncTaskResult or whatever you like) that can get returned with doInBackground. This Object would have two things:

1. The expected result (String in your example)
2. Error code or even if you want, the Exception object itself or a wrapped version of it. Anything that basically will help you handling error if any occurs

I would then return this object to postExecute() and let that method check for the error, if there is then I handle it accordingly, otherwise I take the expected result and do whatever with it.

The object would be something like:

     public class AsyncTaskResult {
            Exception exception;
            T asyncTaskResult;

            public void setResult(T asyncTaskResult) {
                this.asyncTaskResult = asyncTaskResult;
            }

            public T getResult() {
                return asyncTaskResult;
            }

            public void setException(Exception exception) {
                this.exception = exception;
            }

            public boolean hasException() {
                return exception != null;
            }

            public Exception getException() {
                return exception;
            }
        }

And your code becomes :

    /** this would be cool if it existed */
    protected void onError(Exception ex) {
        // handle error...
    }

    @Override
    protected AsyncTaskResult doInBackground(String... params) {
        AsyncTaskResult result = new AsyncTaskResult();
        try {
            // ... download ...
        } catch (IOException e) {
            result.setException(e);
        }

        return result;
    }       

    @Override
    protected void onPostExecute(AsyncTaskResult result) {
        if(result.hasException()) {
            // handle error here...
            onError(result.getException());
        } else {
            // deal with the result
        }
    }