This API specifies a call back to be used when the device receives a state update.
IOTHUB_CLIENT_RESULT IoTHubClient_SetDeviceTwinCallback( IOTHUB_CLIENT_HANDLE iotHubClientHandle, IOTHUB_CLIENT_DEVICE_TWIN_CALLBACK deviceTwinCallback, void * userContextCallback );
iotHubClientHandleThe handle created by a call to the create function.
deviceTwinCallbackThe callback specified by the device client to be used for updating the desired state. The callback will be called in response to a request send by the IoTHub services. The payload will be passed to the callback, along with two version numbers:
userContextCallbackUser specified context that will be provided to the callback. This can be NULL.
NOTE: The application behavior is undefined if the user calls the IoTHubClient_Destroy function from within any callback.
IOTHUB_CLIENT_OK upon success or an error code upon failure.