Change control values on button press

Question

Hi, I've got a situation where I have several numeric controls where you can change different values. I also have several subVIs with control references (as described in this article: http://labviewwiki.org/Control_References) that takes in references to these numeric controls on the mainVI. These subVIs continously read the values in their own threads.
So whenever I change a value on any of the controls, the values does of course change in the subVIs, since they reference to the value of the control.  How would I make the actual value only change only after I clicked the ok button?
To illustrate this I made a VI with an event structure and a separate while loop that continoulsy reads a reference to the control and updats an indicator. I can think of a few cumbersome solutions, whereas I have two controls for every value. The second control would then be hidden and only written to in case of the Ok button press. But having two controls to do something simple as this seems superfluous.
Message Edited by Siniz on 10-20-2009 10:36 AM
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ValueChangeOnButtonPress.vi ‏19 KB

Answer 1

Given what you want to do then I would suggest that you use an Action Engine to contain your data. This has the advantage of decoupling the UI from the subtasks. I would recommend that your action engine consist of an array of clusters. Each cluster would contain the data values, in your case Ki, Kd and Kp for each controller. This has the advantage of reducing the individual values you are dealing with and treats the data for a given controller as a whole. The subtasks could either poll the data looking for a value change. You could even keep track of that in your Action Engine so you would only need to poll to see if the data changed. If it did, then read the data. You would need an index or ID to specify which controller's data you would want to access. The action engine allows you to grow your application if more controllers are added. You should use a typedef to define the cluster. If you wanted to make this more event driven you could use a single notifier shared by your subtasks that would simply indicate a data change event. Part of the data for the notifier could specify which data. That way only interested subtasks would take action. This type of architecture wouldn't add lots of wires to your diagram especially if you used a named notifier.
Regardless of the way you choose to pass the data to the subtasks I would take a look at your UI. I haven't seen it so I can't comment on it specifically. However is you have 40 controls on the front panel at the same time it most likely is a confusing interface. There are ways to reduce the complexity and still provide the same functionality. If you haven't already looked at I would recommend getting the book The LabVIEW Style Book by Peter Blume. If you did reduce your UI to only work with a single controller or a couple of related controllers at a time the Action Engine approach would work nicely since you take your data from the FP and only update the data that has changed. From a UI perspective you have less controls to worry about on your UI and it will probably be easier for the user to understand. From the application's perspective you have decoupled the subtasks from the UI in a very clean way. Another approach would be to use LVOOP for your controller data and processing. Then you simply instantiate a new instance of the class (an object) for each controller that your system is using. This has an added benefit of allowing you to use different controllers and load them at runtime using dynamic dispatching.
PS You are good for the overall Kudo count. Thanks.
Message Edited by Mark Yedinak on 10-20-2009 12:33 PM
Mark Yedinak
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