VI High 3: How to Use Property Nodes in SubVIs through Use of LabVIEW Control References & Refnums


Uploaded by Sixclear on 14.12.2010

Transcript:
>> NARRATOR: In our last episode! We learned about intuitivity and disabling
and enabling front panel objects with property nodes. As we see here, these front panel objects
being enabled or disabled with these property nodes. At the end I asked if there exists
an easy way to modularize what I’ve done and access the same disable property on all
these objects without creating separate property nodes for each object each time I enable and
disable. That’s what we really want and that’s what we’ll do now.
First we’ll look at how we previously accessed the disable property: through these implicitly
linked property nodes. Why are they called that? To differentiate them from explicitly
linked property nodes. Well what’s that? I can create an explicitly linked property
node by simply pulling up a generic property node, this property node can display the properties
of any object, it just needs to be pointed to that object. We do that by creating a reference
to an object. Let’s do that. We’ll copy these controls to a new VI. Ctrl+N is a shortcut.
I’ll right-click on Acquisition Rate and choose create>>reference. Now, I’ll pull
up that same generic property node and wire the reference into the Reference input. Now
I’ve exposed all the same properties of the object with this explictly linked property
node as I had with this implicitly linked property node. The object is the Acquisition
Rate Control. This property node is explicit because I used this reference to explicitly
point it to a particular object, and has the added benefit of not needing a parental advisory.
So why would we want to be so explicit? Let’s examine. There are many reasons. A common
reason is to have a single property node access the same property of multiple objects. We
have a perfect need for an explicitly linked property node in our current Test.vi as these
3 implicitly linked property nodes here and here are accessing the disabled property on
3 different front panel objects, these three. If I want to use one generic property node
on these other two objects I’ll need to create references for those. How can I have this same property node access
these references? Simple, create an array and auto-index it into a For Loop.
Now choose the disabled property, change to write, move this over, create a constant.
Now if I pull up my front panel,
and put this on highlight execution, I can watch as one by one, I will disable each object.
Take off highlight execution, enable them, run them, they’re all enabled. Perfect.
Going back to test.vi. I need to essentially do the same thing in 2 places: disabling here
and enabling here. Rather than make a copy of this block of code twice, we know that
this is a perfect case for a subVI. So I’ll make this new VI into a subVI. To be able
to control whether I enable or disable, I’ll pull this constant outside of the loop and
also create an error cluster going in and going out. Wire these back up, and disable indexing because
I don’t want to have an array of error clusters. This is the section I want to make into a
subVI, so I’ll just select it and go to Edit>>create SubVI. I’ll look at the block
diagram of this new subVI. Let’s clean it up with the block diagram cleanup. And I have
this array of incoming references which corresponds to an array of refnums or reference numbers
on the front panel. This accepts an array of incoming references from a calling VI.
Let’s save this. I’ll call it disable and give it a nice icon. There’s a glyph
already waiting for me. Lovely.
Now I’ll drop disable.vi in place of these existing property nodes and connect everything.
But first we’ll fix the connector pane,
to the 4x2x2x4. Back on test.vi, I’ll make this array of references.
Simply copy this.
Now I’ll see that my test.vi behaves exactly as it did before. I can run it, edit these
controls, when I click on run test, the test is running and I can’t edit these controls,
until the test is finished and they’ve been re-enabled. Disable VI is now a very handy
subVI to be able to use in future applications. We’ll take a look at that in part B of this
video.