Why can't doInbackground method have empty body?

Issue

I have a class that extends AsyncTask. I pass in a list of cholesterol monitors and create the fragment in onPostExecute. However, doInbackground cannot be an empty method and onPostExecute also doesn't override correctly?

private class CholesterolFragment extends AsyncTask<ArrayList<CholesterolMonitor>, Void, Void>`{

        @Override
        protected Void doInBackground(ArrayList<CholesterolMonitor>... arrayLists) {

        }

        @Override
        protected void onPostExecute(ArrayList<CholesterolMonitor> result){
            cholesterol_monitor= result;
            monitorListFragment = MonitorListFragment.newInstance(cholesterol_monitor);
            getSupportFragmentManager()
                    .beginTransaction()
                    .replace(R.id.fragment_monitor_layout, monitorListFragment)
                    .commit();
        }
    }

In my onCreate I pass in the cholesterol monitor list:

monitor_list= this.getIntent().getParcelableArrayListExtra("monitorList");

cholesterol_monitor = (ArrayList<CholesterolMonitor>) monitor_list;
CholesterolFragment cholesterolFragment= new CholesterolFragment();
cholesterolFragment.execute(cholesterol_monitor);

Solution

There's no point in having an async task with an empty doInBackground, at that point you aren't doing anything asynchronously. You may as well just do it directly on the main thread.

But the answer is that doInBackground returns a value. So the body can just be return null; but it needs that return.

Answered By - Gabe Sechan