Control references as subVI input

I have a subVI which accepts control references as input. But these are optional inputs. I have code in the subVI whcih uses the refernecs. I want this code to execute only if the control refernce inputs are wired from the main VI. Is there any way I can check whether the control refernce inputs were wired in the main VI?

You can use Not a Number\Path\Refnum from the Comparison palette or you can type cast the reference to a numeric and check if it is not equal to 0. There are probably some other ways.
Try to take over the world!

Similar Messages

Passing control reference to subVI crashes labview

Hi,
using a image control (as indicator) provided by imaq Vision, I tried to pass the reference of the control to a subVI. On a computer it works and on a other (same labview version, same vision version, same os, same hardware and hardware drivers!), this crashes labview. I tried to close the control refnum at the end of the subVI, but that changed nothing to the issue. Now I use the reference as a global variable and it seems to work...nevertheless, I would like to understand what the issue and if I should remove any passing to subVI of control ref because this can potentially triggers an error. My correlated question is if this global passing is a "fake" workaround or have real chance of improving (this before going through the whole code for changing all passing of reference to subVI)
thanks a lot

Hi,
thank CoastalMaineBird for your answer
How do you know it's this issue which causes the crash?
When I remove this parameter from and the only property node in the subVi that write to it, I have no longer any problem. Moreover, to ensure that's really the "passing", and made a global variable containing the reference to this control and use my original SubVi that do access the control through its reference number
, and it works! In this last exemple, the only change is the way of transmitting the reference
What LabVIEW version?
8.0.1
up to date according Measurement & Automation update tool
Given that one computer works OK, and another crashes, I would say that
you are seeing the effect of something else, not the cause. If passing
a control ref via terminals was fatal, it would be fatal all the time.
You have some other sort of issue, perhaps timing of the different
machines triggers the bug, perhaps running out of memory, perhaps
LabVIEW is corrupted on one machine.... But I don't think changing all
your code to use globals would solve the real problem. Actually, saying that I wonder about problem of synchronisation. I know from Visual C++ that this kind of error happens if two process try to access the same control at the same time. This is typically an error changing from a computer to an other, and mutex or semaphore are the way to deal nicely with that. But does labview contains already such a securisation? If so, the global variable point on a single object and can "fell" the semaphore/mutex. But passing make a copy that will likely have two different semaphore/mutex but will point to a single control! Do someone know if I'm wrong in this idea or not?
Thanks

Pass control references to subVI using Invoke Method

Hi guys,
Can I use <Control Value Set invoke method> to pass some control references to a sub VI, then use the <Run VI invoke method> to run the sub VI with the previously passed data? The control refnums are for some frontpanel controls in the Main VI.
I was able to pass other data but the refnum didn’t work.
Thanks

Hi there, There are a couple examples that use the same method. Check them here:
- Set Control Values and Trigger UI Events in Another VI
- Set Values and Properties of Controls in a SubVI
- Save and retrieve front panel control values
Alejandro | Academic Program Engineer | National Instruments

Finding vi running in subpanel from a subpanel control reference?

I've poked around considerably and cannot find a way to take a control reference to a subpanel control and get the vi reference for the current vi running inside the subpanel.
I know I can save this locally inside the vi containing the subpanel (from the invoke node call to insertvi), but I'm wanting to do this externally from an app that just has references to all the controls.
Any help would be greatly appreciated.
Thanks

If I'm interpreting you correctly, you would like to find the VI reference of the subpanel VI based off one if it's control references that has been passed to some external application from the VI that contains the subpanel VI? See the attached VIs for an example if this is the case.
"VI with subpanel" passes a control reference to "SubVI" which can then get the reference to the "VI in subpanel".
I grabbed the original files from here:
http://digital.ni.com/public.nsf/allkb/0B11E4964685B49F862571430000091E?OpenDocument
Trey B
Applications Engineering
National Instruments
Message Edited by Trey B on 07-24-2007 11:30 PM
Attachments:
VI in subpanel.vi ‏27 KB
VI with subpanel.vi ‏29 KB
subVI.vi ‏8 KB

How can I duplicate a control in a subVI using the reference?

Here's what I want to do. I have a tree control in my main application. I add and delete items dynamically based on user input. If I pass my tree reference to a subVI, I can add, subtract and reorder the items in the tree and the changes are shown on the main tree. How can I duplicate the tree in the subVI? Would I simply pass the tree control in (which I'd rather not do) or is there some other way to accomplish this?
Thanks in advance for any help.
Gary

Here's my attempt. This VI uses a control reference of the old tree and generates a data structure that can be used by the "Edit Tree Items.Add Multiple Items to End" method to add contents to the new tree that should be identical to the contents of the original tree. Note that this VI only works with LabVIEW 8.0 and later, since the afore-mentioned method is not available in previous versions.
I hope this helps...also note that I saw some re-draw issues with LabVIEW 8.0, i.e. after the VI ran, I didn't see the tree displayed properly until I minimized/restored the window, or dragged another window over it. I did not see the redraw issues in LabVIEW 8.2.
-D
Darren Nattinger, CLA
LabVIEW Artisan and Nugget Penman
Attachments:
Duplicate Tree.vi ‏21 KB

Performance issues using control references in Analog control loop?

My main vi of a tensile tester control application calls a number of sub-vi's, including a analog control loop which controls the test. The control loop must update some boolean and digital indicators and respond to user input on the front panel of the main vi during a test.
To simplify my main vi, I moved the control loop code into a sub-vi, and used control references to access the controls and indicators on the front panel. However, this has dramatically affected my loop performance, and the loop can no longer keep up with the acquisition speed.
Do control references always cause such a slowdown? Is there anything that I can do besides moving the code back into the main vi?
Thank You,
David Creech

I have had the same problem. I have discovered other funny things about references also; some kind of memory management (or mismamagement?) is taking place behind the scenes.
Regardless, you can often do away with the references by passing the initial state of a control or indicator into the subvi, changing it inside, and passing the altered state back to the caller. Once back in the caller you update the front panel control or indicator by using a local variable.
One thing to watch out for if using this scenario is the dreaded race condition; this can be avoided using a state machine. Check out
http://www.advmeas.com/goodies/statemachine.html
for a good example. It is a shame that references behave in this way; it limits thier usefulness.
Perhaps someo
ne else will point out a way to utilize them more sucessfully?

Get Control label in SubVI

Greetz All,
Is it possible to get the label of a control that is connected to a subvi from within the subvi without creating a control reference and connecting it to the subvi?
I'm trying to make some new general use subVIs, so I don't want to get a reference to the calling VI and get refs to all its controls and search for the label because what it would search for will change from application to application, so I would have a string input for the label to search for anyway.
Thanks
Ed
Ed Dickens - Certified LabVIEW Architect - DISTek Integration, Inc. - NI Certified Alliance Partner
Using the Abort button to stop your VI is like using a tree to stop your car. It works, but there may be consequences.

I realized the "wire=control" issue late yesterday. And even though I figured out how to get the control name using a variant input ternimal, then use either 'Get Variant Attribute' or convert to XML and parse out the label, there's a good chance the label will not be there anymore for one reason or another, or that there never was one because the wire didn't come from a control.
So I've reverted back to just using a serarate string input to get the needed string into the subVI.
Thanks
Ed
Ed Dickens - Certified LabVIEW Architect - DISTek Integration, Inc. - NI Certified Alliance Partner
Using the Abort button to stop your VI is like using a tree to stop your car. It works, but there may be consequences.

Main VI stops when using control references.

Hi, This is my first question on this forum. I've created an engine simulation VI which uses control references. The main VI has a data acquistion loop and control references. The control references link to another VI that runs an equation loop which continuously calculates engine speed base on data collected in the main VI. The control references work but the main VI data is collected and updated only once when the main VI starts. If I remove the control references from the main VI the daq loop runs fine. Thanks in advance for your help.
Mike

Joe,
Thanks for the response. I do not load the subvi dynamically. I have attached a similar vi to show what I'm trying to accomplish. The DAQ vi reads the input and calculates the power. The power is sent to the "engine momentum sub" vi where the speed, as a function of time, is generated and sent back to the DAQ vi. I created the sub vi to clean up and isolate the DAQ vi from the subvi. I wanted the sub vi to run at a certain speed (by adjusting the wait time)and not affect the DAQ vi. If you input a value of 10 into the DAQ vi and then start it you will see the speed ramp up to 100. While the DAQ vi is running, I need to be able to change the input which would cause the power to change and in turn change the speed. I thought the control r
eferences were the way to go. In my real DAQ vi, I have many more inputs, all which do not update after the first reading. I considered putting the DAQ functions in another subvi and reading the outputs through control references but that seemed too cumbersome.
Thanks again,
Mike
Attachments:
DAQ.vi ‏27 KB
Engine_Momentum_Sub.vi ‏33 KB

Control references and XY graph

hi there,
I was wondering if somebody can help me with passing data to a " XY graph
" not waveform graph [ in a main VI ]
from a sub vI using the concept of a control reference..
p.s: I dont intend to flatten data .
It works fine with waveform graph but there is nothing to show ( even
examples ) me how to do it with XY
graph.
thanks.
ananth

In the example, why is the control reference outside the case statement, since the graph
is only updated when plot=true the ref belongs inside or did I miss something?.
ananth wrote:
> thanks
> and you said it right. that was the problem.
>
> "John Lum" wrote:
> >>>I was wondering if somebody can help me>>with passing data to a " XY
> graph" not>>waveform graph [ in a main VI ] >>from a sub vI using the concept
> of a>>control reference.. >>I don't see any problems here using LabVIEW 6.0,
> and I'm wondering if you're>having trouble with a Variant input or something.>>Here's
> an example of a subVI that spits data into a main VI's XY Graph by>way of
> a control reference>ftp://ftp.ni.com/incoming/xy.zip>>Regards,>John Lum>Na
tional
> Instruments

Data acquisition with control references

I'm a new LabView user and I would like to acquire data in a subVI and display that data in the main VI. I think that I need to use control references and refnums, but I just haven't been able to figure it out. I would GREATLY appreciate any help I could get.
Thank you!

From your description I would guess that the "subVI" has a loop in it that repeatedly reads the FP hardware, and the indicator is inside the loop. Right?
The thing to do is move a lot of the logic in the subVI up to the Main VI--or add the Main's added logic to the subVI, whichever is easier. In the first case, the subVI would go away, in the second, the subVI would become the Main VI.
If you're confused, post your code in V6.0 format and I'll show you what I mean.
Mike...
Certified Professional Instructor
Certified LabVIEW Architect
LabVIEW Champion
"... after all, He's not a tame lion..."
Be thinking ahead and mark your dance card for NI Week 2015 now: TS 6139 - Object Oriented First Steps

Control references/refnums: general info

Please forgive this question, I am a relatively new LV programmer and the help files & manual seem quite poor to me!
I am after some basic information about control references & refnums as I am sure they would be of help to me.
1. What are the main advantages in using them? (i.e. what they can achieve)
2. How are they implemented?
3. How is a control refnum/reference passed from one VI to another programmatically?
Huge thanks to anyone who may be able to shed some light on this topic.
Dan

> 1. What are the main advantages in using them? (i.e. what they can
> achieve)
The references let you access properties and methods of controls on a
front panel. Previously, the access was limited to the diagram of that
panel, and each property node accessed a single particular control.
With control refnums, you can have one property node access an arbitrary
control with the refnum parameter controlling which one. You can also
send the refnums to subVIs meaning that the code can be abstracted to
simpolify your diagram and shared with other panels.
> 2. How are they implemented?
I assume you want to know how to use them. You right click on the
control or its terminal and under the create menu, next to where you can
create an implicit property node, you can also create a Reference node.
The datatype of this node is unique to the type of control that you
created it from, and when wired to a property node, the property node
will show the same properties as an implicit one. As an example, if you
have 8 Boolean buttons on your panel that need to be enabled, disabled,
hidden, colored, labeled, or whatever based upon the state of your
application. You can right click on the eight buttons creating
Reference nodes and build an array of the references. You can now loop
through your array and with one property node, set the properties of the
buttons based upon whatever logic or table of information that you need.
You can also do this in a subVI by passing the array of references to
the subVI.
It is also possible to get control refnums/references from other
properties. For example, a slider will give the reference to its
digital display, a graph will give references to its cursors, etc. It
is also possible to loop through the references of all objects on the
panel inspecting names or types rather than using the Create Reference
popup, but this is more advanced and requires casting the references.
If you really want to know how they are implemented, it is much like
file refnums or VISA refnums. I can give more info if you ask a more
specific question.
> 3. How is a control refnum/reference passed from one VI to another
> programmatically?
>
In the refnum palette there is a Control/VI refnum control. You drop it
on your subVI and right click to set the class. Note that there are
lots of classes arranged from basic to very specific. Class refnums
will convert to more basic automatically, but will not wire if they are
incompatible. So, if you are careful, you can select the class from the
menu and create the control refnum that you can wire to the connector
pane allowing you to pass refnums into the VI. A shortcut that is a bit
simpler is to draw the reference from the diagram to the subVI panel.
It will make the correctly typed control refnum for you, ready to wire
to the connector pane.
That is sort of the basic overview. You probably want to look at the
example -- general/cntrlref.llb/Property Nodes.vi. I also suspect that
the devzone contains other examples showing how they can be used.

Control references vs. global variables

I guess my question centers on the appropriate application of control references.
I am writing a complex program that has a state machine at the top level, and, for one frame of the state machine, a while loop containing a couple subVIs, each of which contains many subVIs. The lower-level subVIs are affected by buttons on the top-level VI. Information from the lower-level VIs must be shown on the top-level front panel within the loop. My question is: what is the best way to do this?
(I have a previous version of the program that I wrote that keeps just about everything on the top level so that I can update the front panel, but this is not at all modular.
In addition, I considered breaking things up into more than on
e front panel, but this doesn't seem to be a good option for this section of this program.)
Last week I read about control references, and decided that this could be the way to deal with this issue. I have not worked with them before, so I want to know: Are control references an appropriate solution for this issue? Is it good programming practice to use them, especially to update data on charts and graphs? How do they compare programming-wise and efficiency-wise to global variables?
Global variables are another solution, I think, but I would have way too many variables to update. I think the advantage with global variables is that one could just insert a global variable in a subVI and not have to wire it up through the different subVI levels, which one would have to do (I think) with control references.
Can you offer any advice?
Thanks!

Paul,
The actual implementation of the solution is up to you. This is indeed a complex question.
I would offer the following advice:
On globals:
Try to avoid them. I try to restrict the use of globals to unidirectional. If you have ever dealt with a race condition, you will know why. Mistakes are often made with globals, and they are quite apt to become the biggest source of bugs in a program, especially in one as large and/or complex as your appears to be. If you must use globals, try using a shift register, or LabVIEW 2 style global instead. Basically, you use an unitialized shift register with two (or more) cases: Read and Write. This prevents race conditions, but only if the VI is non reentrant. However, implementation is still difficult.
Control References:
I also have read and heard about control references. I have had much use for them, for controlling the appearance of controls and indicators (and decoratiopns too, I guess...). However, I would caution you on using them to pass data around. This violates dataflow in a big way, as you are passing around pointers, instead of data. I believe this is difficult to implement, and even more difficult to keep straight. I personally recommend using them only for attributes of FP components, not for passing data.
So, what do I believe is the most elegant solution? I think a data server is your best bet. This is close to a LabVIEW 2 style global, but a little more active. Simply write all of your data into a subVI in any manner, a queue, a FIFO, LIFO, etc. Then, retrieve the data as desired. Buffering, queuing, etc are all handled by the data storage and retrieval subVI. It becomes sort of a small active database. The two sides (storage and retrieval) are independent of each other, and the code is all handled in the function. A basic version is a LIFO, Last In First Out, wherein the data is overwritten constantly. The data is then read by the reading VI, the front panel VI in your case, at any time, and the data is always the latest. You can add complexity as you need, such as making it a FIFO. This is done by simply writing the data to an array, then reading back the oldest value (by reversing the array and reading index 0.)
I believe this is an elegant solution to your problem. It does maintain dataflow, except that time is taken out of the equation, depending on how you look at it. It simplifies your program because you only need to do three things. Write the data handler, then drop in the function into the VI that writes, and the one that reads. It is also flexible in handling the data.
Good luck, and let us all know how you do.

Given array control reference, how do I obtain array size programatically

If an array control reference is passed to a sub-vi, how do I obtain the current length of the array within the sub-vi? I've tried two properties: "NumRows", which as documented, contains the visible number of rows in the array control. "IndexVals" contain the indices of the array element in the upper left corner of the array control. There seem to be no methods for obtaining the current array length. I tried changing the class of the array reference to cluster then using the "Controls[]" property... but this generated a runtime error. What am I missing? Thanks.
Solved!
Go to Solution.

Taki1999 wrote:
There's a lot of casting going on in your subvi.
What is the actual use case? There might be a way to do this which doesn't require the casting and you could work just with the reference that is passed in.
For your method you need to wire in a strict class specifier into the To More Specific Class conversion. I'm not sure how to make the strict class specifier.
I can help with that but first...
Working with arrays on unknown data types is no esy task and determining the size is a special challenge and I did just that in this Nugget that talks about using control references. This task is much easier when you know at development time what is in the array. That is where the strict type casting comes into play.
What I would do...
1) Make sure the contents of the array is a type def (to support data strcuture changes in the future).
2) Go to the FP of the VI that has the array in question and drop a generic control ref control.
3) Ctrl-copy and drag the array in question INTO the the generic ref (still working on the FP). You can tell when you find the "sweet spot" in the ref control because it will switch it appearence. See this mini-nugget for an image where the same thing can be done with que refs.
4) Make the now strict ref a type def.
5) Use the type-def'd ref from step #4 in the sub-VI as the proptype used by the "To More Specific...."
After those changes you should be able to work with array in the sub-VI as if it were in the top level.
BTW:
Doing the above on the control in the sub-VI that brings in the ref would allow skipping the "To more Specific..."
Have fun!
Ben
Ben Rayner
I am currently active on.. MainStream Preppers
Rayner's Ridge is under construction

Can you use a control reference for a graph with two channels of data?

when i try to wire a 2-D array of data to the value property of a graph(strict control reference), it shows a conflict. The value data type only shows up as accepting a 1-D array input. I want to use control references to pass the chart data to my main vi. Will I have to change the waveform graph control reference into an array control reference to make this work?? This would require adding a while loop in the main vi to read the array data and update the graph data??

> when i try to wire a 2-D array of data to the value property of a
> graph(strict control reference), it shows a conflict. The value data
> type only shows up as accepting a 1-D array input. I want to use
> control references to pass the chart data to my main vi. Will I have
> to change the waveform graph control reference into an array control
> reference to make this work?? This would require adding a while loop
> in the main vi to read the array data and update the graph data??
I think the problem is that your waveform graph is set to take one type,
a 1D array of doubles, and you are wiring a different type. While
charts adapt to type when the data is wired to their terminal, they do
not adapt to data wired to their value property. If you change the
datatype of the graph from its terminal, then you should see the value
property change type also and you are set.
Greg McKaskle

How do get an indicator to appear when using control references

Hi, can anyone help with the following?
I've just managed to resolve the problem of getting indicators of a sub VI to appear on the front panel of my main VI and remain active. This was done by using control references. Basically, I created a reference for the control on the front panel of the main VI. I then dragged the reference in the block diagram of the main VI to the front panel of the subVI to obtain a Control Refnum. Then in the block diagram of the subVI I created a property node and linked the indicator and control refnum to it. Then I wired the subVI's connector pane to the control refnums in the subVi front panel. Finally, I copied the subVI icon into the mainVI block diagram
and wired the references to the relevent renum terminals of the subVI connector pane. However, I'm still having a problem with one of the indicators, which I've called 'time limit reached?'. When the VI has reached the end of the run this indicator in the subVI changes from the word 'No' (surrounded by a red box) to 'Yes' (surrounded by a green box). In the sub VI this was done by using a comparison function and linking the visible property node to the 'time limit reached?' true/false boolean. I would like the same to happen on the front panel of my main VI. In this case where should I put my property node and control refnum? I'm unable to link a control refnum to the current visible property node. When I create a visible property node which can be joined to a control refnum then I don't have the option to link it to the true/false boolean. Any suggestions? I have written a small VI which demonstrates the problem if need be.
Thanks, Adrian
[email protected]

I would suggest to use a customized boolean instead of making it visible/invisible, just take a boolean, change boolean text from TRUE/FALSE to YES/NO and change also diferent cases colors, this way, you don't need to play with property nodes. If this can't be done for any reason, using a local / global variable is the only solution that comes to my mind.
Hope this helps

Control references as subVI input

Similar Messages

Maybe you are looking for