[MQTT Dash] Refresh on connect

[Rene J. Martins]

Hi Vadim Mostovoy,

I wonder if it is possible to refresh values on connect so that if someone else updates any topic, it could reflect in my dashboard next time I connect to the broker from MQTT Dash.

Thanks and congratulations for your wonderful app!

Regards,

Rene

[Vadim Mostovoy]

Hi Rene, MQTT protocol has `retained` messages. Read about it for better understanding.

In short, last retained message stored on broker side and sent to the client as soon as client subscribed on topic.

--

Thanks,

Vadim Mostovoy

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[Rene J. Martins]

I've read about retained messages and made a bunch of testing. However, it doesn't seem to work with io.adafruit.com, unfortunately. :-(

Regards,

______________________________________________ Rene J. Martins

[Vadim Mostovoy]

Sorry about that.
Unfortunately there is nothing like "request last data" in MQTT protocol specification.

Client app can only passively listen on topic. The only viable thing is retained message.
It works fine in my and others' environments.
I suggest to contact adafruit and check with them.

--

Thanks,

Vadim Mostovoy

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[Rene J. Martins]

I have just confirmed that io.adafruit.com does not support retained messages (https://io.adafruit.com/api/docs/mqtt.html#retained-values), which is a shame!

Fortunately, I managed to find a workaround for this issue (for those who use io.adafruit.com), thanks to your JavaScript handlers!

Here we go:

On Receive event:

if (!event.data) {

  event.data = {};

}

event.data['MyButton'] = 'done';

On Display event:

if (!event.data) {
  event.data = {};
  event.data['MyButton'] = 'refresh';
}
if (event.data['MyButton'] != 'done') {
  app.publish('user/feeds/myfeed/get', 'get', false, 1);
}

Explanation: If you publish anything into feed/get, it won't be published. However, it will force your subscription to receive data as if it had just been updated! (https://io.adafruit.com/api/docs/mqtt.html#using-the-get-topic)

Regards,

______________________________________________ Rene J. Martins