Re-casting of object from control reference

I feel like this question is likely answered elsewhere, but after days of searching I couldn't find an answer. Sorry if I'm missing the answer in some obvious place.
I'm given a reference to a cluster control and told that the elements of the cluster are all children of parent class A. Using the controls[] property I get an array of the elements, and the value property of each of those elements gives a variant that can be turned into class A. At that point, all of the object oriented overriding and private data stuff works as expected.
So far so good.
But one method I call on those objects changes the private data, and I need to update the control with the updated object. There I get a runtime error because the control isn't A but some child class of A.
I think this is where Preserve Runtime Class comes into play, but since I only get a reference to work with, what do I do? This is especially frustrating because debugging probes show that LabVIEW knows the child class on the wire, but I can't see how to tell LabVIEW to cast down to the class that it knows it has.
For example, is there some way to use the ClassName property of the control to cast the object of class A into the child that the control is expecting?
Solved!
Go to Solution.

nathand wrote:
So your trying to write to the specific control within the cluster, by reference, as a variant, and you're getting an error? What's the actual text of the error?
Really you shouldn't ever be using a front panel object this way, especially one where the user never sees the data in it. For passing data around you should use a wire. Neither a wire nor a DVR will get you the ability to pass an arbitrary cluster, though, which it sounds like is what you're trying to do. With a bit more information we might be able to suggest a better approach.
I don't have the text of the error handy, but it comes from the write value property node and basically says the given variant can't be converted to the type of the control. It happens only when the value is cast to the parent class, which makes sense.
In other words, given a control of child type,
control.value ---> variant ---> to parent ---> variant ---> control.value failes with the error
control.value ---> variant ---> to child ---> variant ---> control.value succeeds
So a solution would be a way to cast to the child instead of to the parent. LabVIEW knows what class the control contains; it is listed in a number of places from the ClassName property through the probe window. The problem is I know of no way to bridge the gap from "LabVIEW knows what class this thing is" to "have LabVIEW cast the variant to that class."
I completely agree that I shouldn't have to ever be using a front panel control this way, but I don't want to get sidetracked into talking about the shortcomings of LabVIEW that have required such a use. Suffice it to say, that is the assignment.

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