flutter_adafruit_mqtt

Goal

The goal of this project is to understand how to "do this in flutter":

• subscribe and publish to AdafruitIO
• log events similar/closest to the rich logging I enjoy in Python

  Non Goal

  There is no error checking. My intent was to learn more like a conversation in which we learn how something works, but we stop short of studying so completely that we address all the "what ifs."

  Thanks to Those that Went Before

• shamblett for his mqtt_client dart package and mqtt_client GitHub. Thank you for your well documented and so far robust code. Thank you for being very responsive and supportive answer questions that I had. Even when the questions clearly showed how clueless I am.
• abachman (Adam B.) for his clear answers to questions on the Adafruit.io forum. Thank you for the persistance and final nudge to help me realize the client id is not the username...um...sure obvious to the rest of you!
• Adafruit for not only Adafruit.IO but the quality customer and community experience. You inspire me to ask myself "How hard can it be?" and answer with "As hard as I make it." And most times I figure it out.
• the logging dart package. While I don't understand everything going on in the code, I was delighted with how easy it was to customize log messages to include stack trace information.

  Code Highlights

  Connecting to Adafruit IO

  The Info You Need

  I'm assuming you have familiarity with Adafruit IO. You've subscribed and published to a feed. There is three pieces of information you need to have on hand when connecting to Adafruit.io:

• the broker name. This is io.adafruit.com
• your username. This is your adafruit.com username.
• your AIO key. This is a secret key generated for your Adafruit IO transactions. You find this within the Adafruit IO web interface.

I put this info into a config/private.json file. Here's a screenshot of where the file goes within the project:

The contents of the file looks like:

{
    "broker": "io.adafruit.com",
    "username": "your username",
    "key": "your AIO key"
}

The helper function _getBrokerAndKey() read the file and turn it into something akin to a dictionary in Python:

  Future<Map> _getBrokerAndKey() async {
    // TODO: Check if private.json does not exist or expected key/values are not there.
    String connect = await rootBundle.loadString('config/private.json');
    return (json.decode(connect));
  }

for example:

  Map connectJson = await _getBrokerAndKey();
    // TBD Test valid broker and key
    log.info('in _login....broker  : ${connectJson['broker']}');

WARNING: As I noted earlier, I do no error checking. The code assumes all is well with the keys and values.

Authenticated connection

The example code that comes with mqtt_client does not authenticate to the broker. I do this by adding:

final MqttConnectMessage connMess = MqttConnectMessage()
    .authenticateAs(connectJson['username'], connectJson['key'])   

authenticateAs to the MqttConnectMessage.

Passing Updates to the Flutter UI

Passing updates requires a subscription to a feed. Check out the subscription code in mqtt_stream.dart.

Streams

This is where the code in Adafruit_feed.dart comes in. It's all about the dance between the StreamController (the Dart library code that has a method to add data to a Stream), the Stream (the Dart library code that contains the data), and the StreamBuilder (the Flutter widget that updates the associated UI component).

Adding Data to the Stream

Adding data happens when this line of code in mqtt_stream.dart runs:

AdafruitFeed.add(pt);

Displaying Data

The _subscriptionData Widget in mqtt_ui_page.dart uses a StreamBuilder to associate the data coming in from the mqtt subscription with a UI element (in this case a Text widget) that displays.

Publishing Data

Publishing is simpler than subscribing. I am hoping it is obvious what's going on if you go from the mqtt_ui_page where the publish button is and follow it into mqtt_stream.dart where the publish method is.

Logging

• [main.dart]() Obviously the entry point. Here is where I initialize how the log messages will print out.

  final Frame f = frames.skip(0).firstWhere((Frame f) =>
  f.library.toLowerCase().contains(rec.loggerName.toLowerCase()) &&
  f != frames.first);

  in this line of code, we're sifting through the stack frames, pulling out the one that contains the name of the dart file where the log message came from. Once we have this glorious piece of info, we can send it to an output stream (in this case, our debug console):

  print('${rec.level.name}: ${f.member} (${rec.loggerName}:${f.line}): ${rec.message}');    

  For example, I set up logging in the mqtt_stream.dart file:

  log = Logger('mqtt_stream.dart');

  (Sadly, i couldn't find a similar library to Python's to get the name of the file the code is currently running) Then in the code I have on line 167 of mqtt_stream.dart:

  log.info('Adafruit client connected');

  when the app runs past this line, the debug console prints out:

  flutter: INFO: AppMqttTransactions._login (mqtt_stream.dart:167): Adafruit client connected

  _Note: The mqtt_client library has its own logging that currently is turned off. This can be toggled on or off by:

  client.logging(on: true);

  which I put in the _login() function within mqtt_stream.dart.