Changing the value of a control in a subvi

[davey31415]

I think the answer is out there somewhere but I've read through many threads found with searches similar to this topic so sorry to repost...

I would like to change the value of a top-level VI control from a sub-vi.  The data is being used as a parameter, I was thinking about using a local/global but I've seen this discouraged.  Is there a way I can do it with references, property, or invoke nodes (or some other suggested method) ?

I am guessing that if I am not using globals I will need to wire into the sub-vi?

Dave

[davey31415]

I'd like to clarify what I am trying to do a bit more...

The sub-vi has a control of the same type as the top-level vi.  The inital control value is being passed into the sub-vi from the top-level vi.  The sub-vi uses the control value in several places through local variables (reading and writing to it)

I would like to modify the vi so the top-level vi control value changes whenever the sub-vi changes the control value that is passed to it.

My last attempt was to make a refnum control in the sub-vi (by dragging from top-level block diagram to sub front panel) and then creating a property node from that refnum control.  Using the property node "value" did not give me the value of the control from the top-level vi as I had hoped.  Wiring it to a terminal that was expecting the same type of control (a cluster of two numerics) caused a wiring conflict.

I noticed elsewhere in the code that the programmer used a text file to save options (unfortunately the control I am working on was not originially included in the options).  There is a vi that, when called, either reads or writes to the text file.  From a C/C++ programming perspective it seems quite odd to me not to just keep all this data in memory and pass it around.  Is using a file to store variables a typical practice in LV programming (even when they are retrieved multiple times during program execution) ?

[altenbach]

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@davey31415 wrote:

My last attempt was to make a refnum control in the sub-vi (by dragging from top-level block diagram to sub front panel) and then creating a property node from that refnum control.  Using the property node "value" did not give me the value of the control from the top-level vi as I had hoped. 

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Make the refnum control an input connector of the subVI, the wire it to a value property node.

In the main VI, create a reference to your desired control and wire it to that connector when you call the subVI.

[davey31415]

I must not have wired the reference, I think I did everything else.

How about using files to store/retrieve data?  It seems to me it would make more sense to use a reference to a cluster throughout the entire program unless data needs to be saved between program uses. 

[altenbach]

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@davey31415 wrote:
How about using files to store/retrieve data?  It seems to me it would make more sense to use a reference to a cluster throughout the entire program unless data needs to be saved between program uses. 

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That really depends on the purpose. Files have the advatage that updated data is typically not lost if the program or computer crashes. 😉

[davey31415]

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@altenbach wrote:

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@davey31415 wrote:

My last attempt was to make a refnum control in the sub-vi (by dragging from top-level block diagram to sub front panel) and then creating a property node from that refnum control.  Using the property node "value" did not give me the value of the control from the top-level vi as I had hoped. 

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Make the refnum control an input connector of the subVI, the wire it to a value property node.

In the main VI, create a reference to your desired control and wire it to that connector when you call the subVI.

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Okay, I've tried that, here's the error I'm running into:

You have connected wires of 2 different types: source is cluster of 2 elements, sink is cluster refnum of 2 elements.

Is there some way to make these compatible (like a cast maybe) ?

Dave

[davey31415]

Never mind, I was creating a property node for the refnum (I guess that's obvious from the error message when you think about it).  I was wondering why there wasn't a reference input for the property node.  I overlooked the 'Property' item near the bottom of the context menu.  I think in the future I will just select 'Property Node' from the Application palette.  Thanks for the assistance!

Dave