This post builds on my Smartish Edge Camera -Azure IoT Direct Methods post adding two updateable properties for the image capture and processing timer the due and period values. The two properties can be updated together or independently but the values are not persisted.
When I was searching for answers I found this code in many posts and articles but it didn’t really cover my scenario.
private static async Task OnDesiredPropertyChanged(TwinCollection desiredProperties,
object userContext)
{
Console.WriteLine("desired property chPleange:");
Console.WriteLine(JsonConvert.SerializeObject(desiredProperties));
Console.WriteLine("Sending current time as reported property");
TwinCollection reportedProperties = new TwinCollection
{
["DateTimeLastDesiredPropertyChangeReceived"] = DateTime.Now
};
await Client.UpdateReportedPropertiesAsync(reportedProperties).ConfigureAwait(false);
}
When AZURE_DEVICE_PROPERTIES is defined in the SmartEdgeCameraAzureIoTService project properties the device reports a number of properties on startup and SetDesiredPropertyUpdateCallbackAsync is used to configure the method called whenever the client receives a state update(desired or reported) from the Azure IoT Hub.
protected override async Task ExecuteAsync(CancellationToken stoppingToken)
{
_logger.LogInformation("Azure IoT Smart Edge Camera Service starting");
try
{
#if AZURE_IOT_HUB_CONNECTION
_deviceClient = await AzureIoTHubConnection();
#endif
#if AZURE_IOT_HUB_DPS_CONNECTION
_deviceClient = await AzureIoTHubDpsConnection();
#endif
#if AZURE_DEVICE_PROPERTIES
_logger.LogTrace("ReportedPropeties upload start");
TwinCollection reportedProperties = new TwinCollection();
reportedProperties["OSVersion"] = Environment.OSVersion.VersionString;
reportedProperties["MachineName"] = Environment.MachineName;
reportedProperties["ApplicationVersion"] = Assembly.GetAssembly(typeof(Program)).GetName().Version;
reportedProperties["ImageTimerDue"] = _applicationSettings.ImageTimerDue;
reportedProperties["ImageTimerPeriod"] = _applicationSettings.ImageTimerPeriod;
reportedProperties["YoloV5ModelPath"] = _applicationSettings.YoloV5ModelPath;
reportedProperties["PredictionScoreThreshold"] = _applicationSettings.PredictionScoreThreshold;
reportedProperties["PredictionLabelsOfInterest"] = _applicationSettings.PredictionLabelsOfInterest;
reportedProperties["PredictionLabelsMinimum"] = _applicationSettings.PredictionLabelsMinimum;
await _deviceClient.UpdateReportedPropertiesAsync(reportedProperties, stoppingToken);
_logger.LogTrace("ReportedPropeties upload done");
#endif
_logger.LogTrace("YoloV5 model setup start");
_scorer = new YoloScorer<YoloCocoP5Model>(_applicationSettings.YoloV5ModelPath);
_logger.LogTrace("YoloV5 model setup done");
_ImageUpdatetimer = new Timer(ImageUpdateTimerCallback, null, _applicationSettings.ImageTimerDue, _applicationSettings.ImageTimerPeriod);
await _deviceClient.SetMethodHandlerAsync("ImageTimerStart", ImageTimerStartHandler, null);
await _deviceClient.SetMethodHandlerAsync("ImageTimerStop", ImageTimerStopHandler, null);
await _deviceClient.SetMethodDefaultHandlerAsync(DefaultHandler, null);
await _deviceClient.SetDesiredPropertyUpdateCallbackAsync(OnDesiredPropertyChangedAsync, null);
try
{
await Task.Delay(Timeout.Infinite, stoppingToken);
}
catch (TaskCanceledException)
{
_logger.LogInformation("Application shutown requested");
}
}
catch (Exception ex)
{
_logger.LogError(ex, "Application startup failure");
}
finally
{
_deviceClient?.Dispose();
}
_logger.LogInformation("Azure IoT Smart Edge Camera Service shutdown");
}
// Lots of other code here
private async Task OnDesiredPropertyChangedAsync(TwinCollection desiredProperties, object userContext)
{
TwinCollection reportedProperties = new TwinCollection();
_logger.LogInformation("OnDesiredPropertyChanged handler");
// NB- This approach does not save the ImageTimerDue or ImageTimerPeriod, a stop/start with return to appsettings.json configuration values. If only
// one parameter specified other is default from appsettings.json. If timer settings changed I think they won't take
// effect until next time Timer fires.
try
{
// Check to see if either of ImageTimerDue or ImageTimerPeriod has changed
if (!desiredProperties.Contains("ImageTimerDue") && !desiredProperties.Contains("ImageTimerPeriod"))
{
_logger.LogInformation("OnDesiredPropertyChanged neither ImageTimerDue or ImageTimerPeriod present");
return;
}
TimeSpan imageTimerDue = _applicationSettings.ImageTimerDue;
// Check that format of ImageTimerDue valid if present
if (desiredProperties.Contains("ImageTimerDue"))
{
if (TimeSpan.TryParse(desiredProperties["ImageTimerDue"].Value, out imageTimerDue))
{
reportedProperties["ImageTimerDue"] = imageTimerDue;
}
else
{
_logger.LogInformation("OnDesiredPropertyChanged ImageTimerDue invalid");
return;
}
}
TimeSpan imageTimerPeriod = _applicationSettings.ImageTimerPeriod;
// Check that format of ImageTimerPeriod valid if present
if (desiredProperties.Contains("ImageTimerPeriod"))
{
if (TimeSpan.TryParse(desiredProperties["ImageTimerPeriod"].Value, out imageTimerPeriod))
{
reportedProperties["ImageTimerPeriod"] = imageTimerPeriod;
}
else
{
_logger.LogInformation("OnDesiredPropertyChanged ImageTimerPeriod invalid");
return;
}
}
_logger.LogInformation("Desired Due:{0} Period:{1}", imageTimerDue, imageTimerPeriod);
if (!_ImageUpdatetimer.Change(imageTimerDue, imageTimerPeriod))
{
_logger.LogInformation("Desired Due:{0} Period:{1} failed", imageTimerDue, imageTimerPeriod);
}
await _deviceClient.UpdateReportedPropertiesAsync(reportedProperties);
}
catch (Exception ex)
{
_logger.LogError(ex, "OnDesiredPropertyChangedAsync handler failed");
}
}
The TwinCollection desiredProperties is checked for ImageTimerDue and ImageTimerPeriod properties and if either of these are present and valid the Timer.Change method is called.
The AzureMLMetSmartEdgeCamera supports both Azure IoT Hub and Azure IoT Central so I have included images from Azure IoT Explorer and my Azure IoT Central Templates.
When I modified, then saved the Azure IoT Hub Device Twin desired properties JavaScript Object Notation(JSON) in Azure IoT Hub Explorer the method configured with SetDesiredPropertyUpdateCallbackAsync was invoked on the device.
In Azure IoT Central I added two Capabilities to the device template, the time properties ImageTimerDue, and ImageTimerPeriod.
I added a View to the template so the two properties could be changed (I didn’t configure either as required)
In the “Device Properties”, “Operation Tab” when I changed the ImageTimerDue and/or ImageTimerPeriod there was visual feedback that there was an update in progress.
Then on the device the SmartEdgeCameraAzureIoTService the method configured with SetDesiredPropertyUpdateCallbackAsync was invoked on the device.
Once the properties have been updated on the device the UpdateReportedPropertiesAsync method is called
Then a message with the updated property values from the device was visible in the telemetry
Then finally the “Operation Tab” displayed a visual confirmation that the value(s) had been updated.
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