Extends AsyncTask , Check Activity finished or not before send back to UI Thread. and change execute to THREAD_POOL_EXECUTOR

SimpleBackgroundTask.java

import android.annotation.TargetApi;
import android.app.Activity;
import android.os.AsyncTask;
import android.os.Build;

import java.lang.ref.WeakReference;

abstract public class SimpleBackgroundTask<T> extends AsyncTask<Object, Void, T> {

    private WeakReference<Activity> weakActivity;

    public SimpleBackgroundTask(Activity activity) {
        weakActivity = new WeakReference<Activity>(activity);
    }
    @Override
    protected final T doInBackground(Object... voids) {
        return onRun(voids);
    }

    private boolean canContinue() {
        Activity activity = weakActivity.get();
        return activity != null && !activity.isFinishing() ;
    }

    public Activity getActivity(){
        return weakActivity.get();
    }

    @Override
    protected void onPostExecute(T t) {
        if(weakActivity != null && canContinue()) {
            onSuccess(t);
        }
    }

    @TargetApi(Build.VERSION_CODES.HONEYCOMB)
    public SimpleBackgroundTask execute() {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
            executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
            return(this);
        }
        return (SimpleBackgroundTask)(super.execute());
    }

    abstract protected T onRun(Object... voids);
    abstract protected void onSuccess(T result);

}