Obtaining reference to cluster with no indicator

[Newbie217]

Hello all,

I am trying to create a program that passes in a cluster of plots to a subvi that accepts generic controls. The reason for this is the number of elements in the cluster may change and I want to create a modular subvi that does not always break the connector pane. I'm guessing an array would actually be a better solution for this example, but in any case I want to see if there is a way to get this specific program working.

 The subvi then converts this generic control to a cluster control using the "to more specific class" function. Using property nodes, I can then index each element and obtain the data information I want.

The problem I am running into is that I receive the ERROR 1057 each time I try to convert the generic control into a cluster control. I am first typecasting the cluster and I'm pretty sure I am doing this incorrectly. I'm not sure how to go about fixing this as I have minimal experience using typecasting functions. I do notice that if I first create an indicator for the clusters, then i can easily convert this indicator to a more generic class, and pass this into the connector pane with no problems. For my application, I would like a way of obtaining a reference to a cluster without having to create an indicator each time. Hopefully there's an easy solution to this problem. Thanks for the help!

[CoastalMaineBird]

You're way off base here, with serious round-peg, square-hole issues.

First, a GRAPH is a thing on the front panel, which displays one or more PLOTs.  There's no such thing as a reference to a plot.

When you bundle the three graph refs (upper left), you have a data structure with three items in it. 

When you cast that to a single control ref, you throw away most of the data.

By definition, a cluster is for a fixed number of various type items.

By definition, an array is for a variable number of identical items.

If you want to pass a variable number of graph refs to a subVI, then build an array using the refs, and pass it.

You are fighting the system, instead of letting it work FOR you.

[MattBradley]

Instead of passing in a cluster of references, try passing in an array of references.  Then you won't need the typecasting at all.

As for your question "Is there a way to obtain reference to a cluster that has no control?"  Well, sort of.

First of all,  a control reference is a reference to a specific front panel object.

That being said, you can put one on the block diagram by selecting (from the function palette) Programming-->Application Control -->Class Specifier Constant  and then from the object menu, select Select VI Server Class -->Generic-->GObject-->Control-->Cluster... but I'm not really sure what (if anything) that would get you.

[MattBradley]

For the record, I was distracted in the middle of writing my post and did not see Steve's.  Great minds think alike.  So do mediocre ones...   🙂

[nathand]

You can't create a reference to an object that doesn't exist.  A control reference points at a specific front-panel object (control or indicator), not to data.  Your typecast tells LabVIEW to treat the cluster data as if it were a reference, but since that reference is garbage and doesn't point at anything, LabVIEW gives you an error.

EDIT: looks like Matt beat me to it (same phrasing, even!)

Message Edited by nathand on 03-26-2009 05:46 PM

[CoastalMaineBird]

Great minds think alike.  So do mediocre ones.

Whether we are the former or the latter is left as an exercise for the reader...

[MattBradley]

Law of averages says that the more people in the group that posted the same thing, the more likely they are to be mediocre.  (Since great minds are rare)

Damn.

[CoastalMaineBird]

Law of averages says 

Crap, now I have to go get my lawyer involved?