private class backgroundLoadList extends AsyncTask<Void, Integer, ArrayList<CustomDataStructure>> {

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        mSpinner.setVisibility(View.VISIBLE);
    }

    @Override
    protected ArrayList<CustomDataStructure> doInBackground(Void... voids) {
        ArrayList<CustomDataStructure> result = getTabNetworkList();
        return result;
    }

    @Override
    protected void onPostExecute(ArrayList<CustomDataStructure> customDataStructures) {
        adapter.listItems.retainAll(customDataStructures);
        adapter.listItems.addAll(customDataStructures);
        adapter.notifyDataSetChanged();
        mSpinner.setVisibility(View.GONE);
        super.onPostExecute(customDataStructures);
    }
}

private ArrayList<CustomDataStructure> getTabNetworkList() {
            CustomDataStructure item;
            ArrayList<CustomDataStructure> items = new ArrayList<>();
            try {
              item = new CustomDataStructure(getResources().getString(R.string.itemDescType), networkRoaming);
              items.add(item);
            // long list with further items is added below...
            } catch (SecurityException e) {
            // Exception occurs on the next line because the context is not available anymore for getting the resources...
              item = new CustomDataStructure(getResources().getString(R.string.itemInfo), getResources().getString(R.string.textNotAvailable));
              items.add(item);
            }
            return items;
    }