Change notification in Azure IOT Hub device twin

Question

I'm working on IOT Hub device twin, and I couldn't find a way to get a notification on the device when a property is changed in the twin.

I know that there's a solution for that on the IOT Hub side, using a dedicated route, but how can I get a notification on the device when the twin has changed?

I've looked into the DeviceClient class but couldn't find anything relevant.

What am I missing?

you should use the SetDesiredPropertyUpdateCallbackAsync method to subscribe the notification on the desired property changes. — Roman Kiss

rido rido · Accepted Answer · 2021-05-07T01:48:01

Depends on the SDK or MQTT library.

For, C, C#, Java, JS and Python you can start here:

https://docs.microsoft.com/en-us/azure/iot-pnp/concepts-developer-guide-device?pivots=programming-language-csharp#implement-telemetry,-properties,-and-commands

From the C# doc


await client.SetDesiredPropertyUpdateCallbackAsync(async (desired, ctx) => 
{
  JValue targetTempJson = desired["targetTemperature"];
  double targetTemperature = targetTempJson.Value();
TwinCollection reportedProperties = new TwinCollection();
TwinCollection ackProps = new TwinCollection();
ackProps["value"] = targetTemperature;
ackProps["ac"] = 200;
ackProps["av"] = desired.Version;
ackProps["ad"] = "desired property received";
reportedProperties["targetTemperature"] = ackProps;
await client.UpdateReportedPropertiesAsync(reportedProperties);
}, null);

For raw MQTT clients see https://docs.microsoft.com/en-us/azure/iot-hub/iot-hub-mqtt-support#receiving-desired-properties-update-notifications

note: You will find the term "change notification events" usually referring to service side events.

Change notification in Azure IOT Hub device twin

1 Answers