Saving sensor data from Android device and sending all data to server

I'm having a bit of trouble as I am somewhat new to Android development. I'm attempting to read in sensor data, temporarily save that data to a database, and do a bulk insert to a server I created so that I can visualize the data online.

I have my activity that is a SensorEventListener, and I have each event's values being written out to TextViews. I'm reading event data just fine. I assumed that sending data to a server too frequently could be a problem, so I decided to have the saving of data to the internal db for my Android app be initiated via the click of a menu button and the act of taking that data from the internal db and sending it to my server initiated with a different menu button.

My onSensorChanged(SensorEvent event) method looks like:

@Override
public void onSensorChanged(SensorEvent event) {        
    // Accuracy is handled in the onAccuracy Changed ( - 1 )
    for (int i = 0; i < mTextViews.length - 1; i++) {
        mTextViews[i].setText("Value " + i + ": " + event.values[i]);
    }

    if (mSensorEvents == null) mSensorEvents = new ArrayList<>();
    if (mSensorEvents.size() < VALS_MAX) {
        mSensorEvents.add(event);
    } else {
        mSensorManager.unregisterListener(this);
        new SensorEventLoggerTask().execute(mSensorEvents);
    }
}

As I said earlier, the saving and sending actions are initiated via menu buttons, and here is where I handle that:

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    int id = item.getItemId();
    if (id == R.id.action_save_data) {
        mSensorManager.unregisterListener(this);
        new SensorEventLoggerTask().execute(mSensorEvents);
    } else if (id == R.id.action_send_data) {
        new SendSensorDataTask().execute();
    }

    return super.onOptionsItemSelected(item);
}

Those tasks look like this:

private class SensorEventLoggerTask extends AsyncTask<List<SensorEvent>, Void, Void> {

    @Override
    protected Void doInBackground(List<SensorEvent>... events) {
        for (int i = 0; i < events.length; i++) {
            SensorEvent event = events[0].get(i);
            String value = Arrays.toString(event.values);
            long timestamp = (new Date()).getTime() + (event.timestamp - System.nanoTime()) / 100000L;
            ContentValues values = new ContentValues();
            values.put(SensorDataHelper.COL_ACCURACY, event.accuracy);
            values.put(SensorDataHelper.COL_NAME, mSensorName);
            // TODO: get the email from the user
            values.put(SensorDataHelper.COL_EMAIL, "jakehockey10@gmail.com");
            values.put(SensorDataHelper.COL_TIMESTAMP, timestamp);
            values.put(SensorDataHelper.COL_VALUE, value);
            getActivity().getContentResolver().insert(SensorDataProvider.CONTENT_URI, values);
        }
        return null;
    }
}

and...

private class SendSensorDataTask extends AsyncTask<String, String, String> {
    private List<HashMap<String, String>> mData = null; // post data

    /**
     * constructor 
     */
    public SendSensorDataTask(){}

    /**
     * background
     */
    @Override
    protected String doInBackground(String... params) {

        Cursor query = getActivity().getContentResolver().query(SensorDataProvider.CONTENT_URI, null, null, null, null);

        return null;
    }
}

The query method in my SensorDataProvider class just does this:

@Override
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, 
                    String sortOrder) {
    Cursor cursor = getDatabase(false).rawQuery("select * from table", null);
    return cursor;
}

As you can see, I don't have the post request happening yet, but that's because I'm not quite sure how to do it, although I've found some examples online. But I can't get the records I've added to my internal db out and if I can figure that out, my next step would be to create JSON objects out of those records and make a POST request.

From what you see, is there some advice you have for me? Am I approaching this the right way? Where am I screwing up? Please let me know if you need me to post any more snippets. I would really appreciate some guidance...