I using an event structure for an input box and also for hardware input

Question

Hi there!
I have many input boxes and display boxes on my user interface and i have a case for it in the event structure. If the user changes the values of the input boxes, the particular event case writes this new value to the hardware. However, in the timeout section of the event structure, we read the inputs from the hardware and we set the value for its related display object.  Within the timeout section i set the value for the related user interface display component, by making use of the property node value.
Furthermore, for most of the display components, i have a event case for a value change associated with it. In that event case, i check for range errors and so forth.
My assumption was that when i read the value in from the hardware and set the property node value, the user interface component's value will change and it would then trigger the event of the value changed for that component. 
My assumption worked to the point of updating the component's value, however, it did not trigger the event  for the value changed for this component.
Please advise me on how to achieve what i wish to.
Thanks.
Regards,

Answer 1

Local variables are actually much more efficient than property nodes as far as execution speed goes. Take that same VI and delete the property node and instead write to a local variable inside the loop. You'll see the speed nearly identical to writing directly to the indicator. But note that variables also cause a copy of the data to be created. So if you're just using the "Value" property, you're much better off using a local variable. But don't use both at the same time. If you are reading/writing other properties when you update/read the value, you might as well use the value property.
Sometimes you can't get around using either variables or property nodes. Initializing controls to saved values from an ini file is one example. But in this case, they are only written to once as the application starts so the performance hit is negligible.
One thing you can do is store values in a shift register as they are read and pass this through your application so the last value read can be accessed from anywhere. You can even create a cluster that runs through the shift register to hold several values in a single register. This can be expanded a bit farther to create what's called a Functional Global. This basically a subVI with a While loop that only runs once on each call. It has a shift register to store data and a Case structure to Read or Write data into the register. There's a pretty good example that ships with LabVIEW showing how these work. Open the Example finder and search for "Functional Global Communication". This example shows how to use them to pass data between two independent loops, but they work just as well in a single loop application.
One of the big advantages of these Functional Globals over the standard LabVIEW Globals and local variables is that you can add cases to manipulate the data in addition to just storing it. Also, since it's a subVI, access to the data is protected to one caller at a time whereas variables can have multiple reads and/or writes at the same time. This can cause race conditions.
Hope that helps a bit.
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.