Base Loader for Android

BaseLoader.java

public abstract class BaseLoader<T> {
    AsyncTask<Void, Void, Void> task = new AsyncTask<Void, Void, Void>() {
        @Override
        protected void onPreExecute() {
            isNotReady = false;
            isError = false;
            isRunning = true;
        }

        @Override
        @Nullable
        protected Void doInBackground(Void... params) {
            try {
                lastResult = load();
            } catch (RuntimeException e) {
                lastResult = null;
                isError = true;
                isNotReady = false;
            }
            isRunning = false;
            return null;
        }

        @Override
        protected void onPostExecute(Void result) {
            deliverResults();
        }
    };

    private void deliverResults() {
        if (isError) {
            onLoadError();
        }
        if (!isNotReady) {
            onDataLoaded(lastResult);
        }
    }

    private T lastResult;
    private volatile boolean isNotReady;
    private volatile boolean isError;
    private volatile boolean isRunning;

    private final Set<Class<?>> observedModels;

    protected abstract T load();

    public BaseLoader() {
        observedModels = observedModels();
    }

    public void reload() {
        start(true);
    }

    public void start() {
        TeacherApp.bus().register(this);
        start(false);
    }

    private void start(boolean forceReload) {
        if (forceReload) {
            task.cancel(false);
            task.execute();
        } else if (lastResult == null) {
            if (!isRunning) {
                task.execute();
            }
        } else {
            deliverResults();
        }
    }

    public void unregister() {
        TeacherApp.bus().unregister(this);
    }

    public abstract void onDataLoaded(@Nullable T data);

    protected abstract void onLoadError();

    protected Set<Class<?>> observedModels() {
        return Collections.emptySet();
    }

    @Subscribe
    public void onModelUpdate(ModelUpdate modelUpdate) {
        if (observedModels.contains(modelUpdate.modelClass)) {
            reload();
        }
    }

    protected void setLoadError() {
        isError = true;
    }

    protected void setNotReady() {
        isNotReady = true;
    }
}