How to use ReadPropertyMultipleRequest

[mcmayer]

I'm starting to go round in circles with ReadPropertyMultipleRequest...

My understanding is that I need to pass in a BacnetAddress and a List<BacnetReadAccessSpecification>. Each BacnetReadAccessSpecification has a BacnetObjectId and a List<BacnetPropertyReference>. And a BacnetPropertyReference is a bacnet property ID (a uint, e.g. 85 for PRESENT_VALUE) and an array index.

So, as an example, if I wanted to get PROP_PRESENT_VALUE, PROP_DESCRIPTION, PROP_UNITS for some ANALOG_VALUE of instance 0 I think I should do this:

var adr = new BacnetAddress(BacnetAddressTypes.IP, "192.168.0.123:47808");
var objId = new BacnetObjectId(BacnetObjectTypes.OBJECT_ANALOG_VALUE, 0);

var propRefs = new List<BacnetPropertyReference>();
propRefs.Add(new BacnetPropertyReference(85, 0));    // PROP_PRESENT_VALUE
propRefs.Add(new BacnetPropertyReference(28, 1));    // PROP_DESCRIPTION
propRefs.Add(new BacnetPropertyReference(117, 2));   // PROP_UNITS

var spec = new BacnetReadAccessSpecification(objId, propRefs);

var specs = new List<BacnetReadAccessSpecification>();
specs.Add(spec);

IList<BacnetReadAccessResult> results;
bacnet_client.ReadPropertyMultipleRequest(adr, specs, out results);

This is always giving me an error ERROR_CODE_PROPERTY_IS_NOT_AN_ARRAY. I'm probably interpreting the purpose of the various objects the wrong way.

Can someone help out?

[gralin]

@mcmayer How about doing it like this:

var results = await bacnet_client.ReadPropertyMultipleAsync(adr, objId,
    BacnetPropertyIds.PROP_PRESENT_VALUE,
    BacnetPropertyIds.PROP_DESCRIPTION,
    BacnetPropertyIds.PROP_UNITS);

[mcmayer]

I didn't know about these Async calls. I can give your suggestion a try.

But I still would like to know how to use these BacnetPropertyReference and BacnetReadAccessSpecification Lists.

[jreisman]

I ran into the same problem when trying to use ReadPropertyMultipleRequest() and found that I had to change my BacnetPropertyReference from: new BacnetPropertyReference((uint) BacnetPropertyIds.PROP_PRESENT_VALUE, 0);

To: new BacnetPropertyReference((uint) BacnetPropertyIds.PROP_PRESENT_VALUE, System.IO.BACnet.Serialize.ASN1.BACNET_ARRAY_ALL);

I guess if you specify an index at all it wants to require it to be an array, but BACNET_ARRAY_ALL will let it accept non-array values.

[gralin]

Correct, this is a design flaw made by the original authors. I totally agree that this is not intuitive, even though under the covers indeed the index is always sent. That's why I added some suplement methods (the async ones) to make life easier. In the future I was planning on breaking backward compatibility and rewritting the API so it makes more sense.