Invoke, property nodes

Could someone please direct me to some reading material about Property nodes and Invoke nodes? I need a basic explanation of what where how and why! Thanks,
Ivanka

Property nodes and invoke nodes let you access the more specific properties and methods of a control.
An easy way to think if this is properties nodes let you manipulate characteristics of a control like color, labels, and etc. and the actual properties change based control. Invoke nodes let you access possible actions of a specific control.
Due to the fact that properties and methods change based on the control, to do further research on the specifics on what is possible using these nodes, you must do control specific research which will discuss this specifically.
If there is something more I could clear up for you please let me know! Have a great day!
Allan S.
Applications Engineering
National Instruments

Similar Messages

Is it better to use Invoke nodes or property nodes to set/get control values?

I have a series of VI's that run in parallel, each to manage different functions- pumping, sensing, a fluid flow model, an experiment generator/runner.
These need to exchange data, which I am currently doing using invoke nodes (that are all in subVIs), using methods "Set control value" and "Get control value". I find that every now and then (perhaps 1% of the time) the data isn't exchanged correctly and therefore the system doesn't work. I can imagine how "set" could go wrong if they happen simultaneously, and can devise ways of preventing this. However, the "Get" method suffers from the same problem. This is a major problem, because I want to leave it running for several hours.
I could in
principle achieve the same thing using property nodes and find myself wondering if this might be more reliable. But I don't want to change over only to find it makes no difference!
Can anyone advise?

You can use some kind of syncronization such as queues, occurances, or notifiers but I think the easiest way would be to create and action engine. This was only one action can execute at a time avoiding a "race condition". Possibly a write action and a read action might help. You also can add queues or notifiers into this concept. hope this helps.
BJD1613
Lead Test Tools Development Engineer
Philips Respironics
Certified LV Architect / Instructor

How to create a specific property node w/ VI script

I am writing a VI script to work with some multi column listboxes. I need it to create a property node that gets a reference to the ItemNames field. I see that I can create a property node via the invoke node method Create.Property Node, but how to get the ItemNames field specifically I so far can't figure out. Can anyone help?
To be clear, I am writing code that looks like this:
...and when I run the script, I want it to produce this:
Right now it produces the MCL as expected, via the New VI Object node...but I don't know how to get the ItemNames created automatcially. I thought it might be in the PropItems array but so far no luck.
thank you
Solved!
Go to Solution.

The output of "PropItems[]" will be a one element array. Index that element and wire the reference to an invoke node. Select the method "SetProperty".

Tree Control Property Node for Accessing "Child Text" String Array

When adding items to a tree control using the EditTreeItems invoke nodes, the inputs include "Child Tag", "Item Indent", "Child Only?", "Glyph Index", "Child Text", and "Left Cell String" as can be seen in this screenshot.
There are property nodes for the tree control for accessing each of these elements, except for the "Child Text", which is an array of strings. It is possible to access this data as outlined in this forum post, but this method is somewhat involved and round about.
I suggest that a property for the Tree class be created to access the Child Text array directly.

The work around only works if you do not have an empty string element some where in the middle.
At lest could the "Active Celltring Property" read return an error when you have gone beyond the end of the array.

Cursor: Bring to Center via Property node?

The pop-up menu on the Cursor Legend for graphs includes an item: Bring to Center which moves the active cursor to the center of the plot.
Is this capability available programmatically? An Invoke Node method or Property Node? I would like to have a button on the FP which "retrieves" a free cursor. I can see complicated ways using Cursor Position and Scale: Range property nodes. I could not find anything as simple as the pop-up menu.
Lynn

Bublina wrote:
It works OK, but I used it and I remember it failed to work for extreme zoom levels (nothing happened)
Do not remember if the inbuilt functionality failed aswell.
Edit: It did
I take the Edit as "it fails as well". At least, it wouldn't surprise me if you meant it differently.
The reason:
Extreme zoom levels usually mean, that both endpoints of the scale do have a very small difference. Since the center is (at least in altenbach's code and i assume that the context menu function works similar) the average of both endpoint values, the difference between endpoint and average cannot be covered by the used numeric representation. So it computes an average, but that equals to one of the endpoints......
So this is rather a "works as expected" issue, even if not very nice and most likely considered a bug by the user (without above explanation).
Norbert
CEO: What exactly is stopping us from doing this?
Expert: Geometry
Marketing Manager: Just ignore it.

Updating a property node from a sub-vi

I want to have a string indicator box that updates as my program moves along, i have been using the property node this works fine in the main vi but now i want to update it from a sub iv. any ideas?

Tip: The easiest way to accomplish this is to do the following:
In your top-level VI that has the control right-click on it and select Create-->Reference. This will allow you to place a reference in top-level VI's block diagram.
Create a new VI that will be your subVI.
Drag and drop the reference object from the block diagram of your top level VI to the front panel of your new subVI. This will create a reference control on your subVI that is of the same type as the control on your top-level VI.
Connect the reference control on your subVI to a connection terminal, and then wire the reference object in your top-level VI's block diagram to the subVI's input terminal.
Then, in your subVI you can just use the standard "Property" and "Invoke" nodes to fiddle with the control.

Table property node.

Dear,
I am a beginner in using a table.
My attachment and image explain my problem.
By clicking the left mouse key, the cell background color can be changed.
This color is used as three states contoller.
A string in each cell represent the state of the color. (1:1 corresponding with color).
My problems are
1. I didn't write to modify the cell position. But some cells are moving horizontally(by 2 or 3 column) in one row.
One of attachement explained the snapshot of the problem.
2. In real time, I want to update the state string in active cell. the property node result, "Set cell value", is strange.
Of course, I tried to update whole table by using shift registered array.
But, only deactivating the cell by moving the activation to other cell, the string was updated.
3. I want to use the table as a indicator: I want NOT to write some string in any cells of the table.
As I mentioned, some mouse clicking is preferred. How can I do?
Attachement: 1: LV8.0 code, 2: snapshot image
메시지가 04-14-2007 02:17 AM에 labmaster에 의해 편집되었음
Attachments:
bbb.PNG ‏35 KB
table.vi ‏53 KB

Hi Labmaster,
This is an interesting issue, and something that I am going to investigate further. It appears to have something to do with using the invoke node to change cell values within an event structure that is not working. I tried putting a one button dialog box inside that event case to let the user know that the event had fired, and interestingly enough the value changes then. This is likely a LabVIEW bug of some kind.
By the way, you have some funky effects going on in that table!
Best regards,
-Sam F, DAQ Marketing Manager
Learn about measuring temperature
Learn how to take voltage measurements
Learn how to measure current

Use property node

When I right click on a property node or invoke and then click on help for +++ For example, click " Help for border" and notthing come up? How do I know how to use that specific property since there are so many in Labview.

It never works?
"Border" is a property I'm not familiar with, with which element is this connected?
A good one to verify is the 'bounds' property of an item (it is included in almost everything)
Maybe you didn't install the LV help files?
Ton
Message Edited by TonP on 10-13-2006 09:49 AM
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Attachments:
helpforprops.PNG ‏4 KB

Where can I find docs on all the property nodes

Are all the property nodes for things like waveform charts and graphs documented somewhere. I have looked throught all the .pdf files that came with LV ( at least I think I have ) and haven't been able to find what I'm looking for.
If someone could point me to where all these are documented I would be most appreciative.
Thanks.

The LabVIEW Help describes every VI Server property and method. The easiest way to find the help for a specific property and method is to select the property or method in the Property or Invoke Node, right-click the node, and select Help for xxx from the shortcut menu, where xxx is the name of the property or method.
In LabVIEW 6.0, you can browse the property and method help by selecting Help>Contents and Index, clicking the Contents tab, and navigating to Networking in LabVIEW>Properties and Methods.
In LabVIEW 6.1, select Help>VI, Function, & How-To Help, click the Contents tab, and navigate to Programmatically Controlling VIs>VI Server Properties and Methods.
Kelly H
LabVIEW Documentation
National Instruments

Property node standard error in functionality - odd behavior

I am getting what I would consider unusual behavior from a property node when there is an error on the error cluster input. The Help for the VI indicates this node has Standard Error In functionality, which I interpret as if there is an error on the input then the node does not run and the error is simply passed through to the output.
The behavior I'm getting is that the error gets passed through, but the properties of the node also get passed out with the data that was present the last time the node was called (including when it wasn't this specific node, but a different property node within the same VI that has the same property outputs).
In Psuedo code, this is what I'm doing:
Use Invoke node to call a method from a DLL (which sends a command to a device and gets its response).
Pass the method reference to a property node, which then outputs the properties of the method (the response from the device).
This works fine when everything is as it's supposed to be (device I'm communication to is connected, etc.).
If I disconnect the device completely and then run the VI again, I get the property outputs from the previous communication out of the property node, which are obviously not valid as the device isn't even connected. This happens even if the command I sent to the device is not the same; Command1 is sent and gets valid response, disconnect device, command2 is sent and I get response for command1 from the property node of command2. Command1 and command2 are in different cases of a case structure.
At first I thought there might be an issue with the DLL functionality (and there might be) reporting stale data, but before that is even an option it seems the property node shouldn't even be possible to have data output when the node is supposed to be bypassed entirely when an error is passed in.
Is this supposed to happen? Am I missing something?

Coincidentally, this week I ran into what appears to be the same behavior with the Scan from String function, and I thought of this thread. It doesn't help solve your problem, but maybe it's useful to know that this behavior happens in other built-in functions, not just Property Nodes. I started a new thread to look at this more generally.

IVI-COM Vi's or property nodes?

I'm fairly new to IVI-COM instrument drivers and have up until now been using the supplied IVI-COM Vi's for the instrument I'm doing a driver for. However I'm finding that more and more it's making sense to just use a property node to set things such as Start Frequency etc so I'm thinking I might just use them for everything from now on.
All I really want to know is are there any major issues with doing this - and is it something is recommended to be done - just really want reassurance that if I take the route of using property nodes I won't get bitten on the arse by something that I don't know about.
Any thoughts happily received,
David Clark
CLA | CTA
CLA Design Ltd
Hampshire, England

Hi David,
I'm guessing that you've got a bunch of LabVIEW vi's from the vendor - that are basically wrappered IVI-COM calls? (If you can tell me where to download the driver from I can look in more detail). The low level IVI-COM calls will just use ActiveX (so property nodes and invoke nodes) to access the COM object.
Whether you use the wrappered vi's or the lower level calls is up to you, it will depend on the level of flexibility that you require. For some configuration settings for the instrument there might not be a ready built vi - so you may have to use the lower level calls to acheive it. (A bit like the usual plug and play instrument drivers, versus low level calls directly using VISA - which may or may not give you an idea - depending on whether you've used them!).
Take a look at the following tutorial which might give you some more pointers:
http://zone.ni.com/devzone/cda/tut/p/id/4505
I guess one point to bear in mind is that the vendor can at any time change the ActiveX methods and properties with a new release of the driver (a bit like Microsoft have done in the past with things like media player and office) which may leave code you've generated with broken wires, if you are using their wrappered vi's then its possible that they'll keep the wrapper and change whats inside so that its seamless to the end user. - (Its also possible that they could update the automation servers version number which would result in a non working vi - but may not result in broken wires, working with the vendors LabVIEW API should solve these issues - since they will have re-linked them specifically to each version)
Another factor that should help you make up your mind is how well documented each of the options are - they may have put more time into the friendly end user vi's than they have to the API?
But if you're generating your own driver, then it will probably be more useful to you to strip away some of the abstraction to get more efficient results.
I hope this helps - perhaps other members of the NI community can give you their experiences
Hannah
NIUK & Ireland

Add Intellisense support to the property node

I really hate having to dig through a long hierarchy of menus when I know what I want:
Visual Studio (and other MS and non-MS products) have a feature called Intellisense, which is meant to make this easier. Basically, as you type, it pops up a list of matching objects, based on context, so you can quickly select what you want:
It would be nice if LV had a similar feature - click on a property in the property node using the text tool (or Ctrl+click if using the auto-tool) and now you can type in the property name and you will get an Intellisense-like pop-up, which will have all the relevant properties.
Specific features it could have:
It should know all the relevant names - full names with the hierarchy (Boolean Text.Font.Color), long names (Mechanical Action) and short names (MechAction). This could probably be similar to how Quick Drop handles shortcuts or they could simply appear as separate items.
It should be context sensitive. If the class is Boolean, then there's no need to have Listbox properties in the list.
It should match all the properties which include the search string (so "in" on a boolean would match both "Indicator" and "Strings[]") and only them.
It should have the ability to use caps for acronyms (e.g. in the above screenshot you could use "BT" instead of "Boolean Text", similar to what appears in this video).
It could probably also work on the invoke node, although there it's less needed.
It could probably also be used to quickly select a class if you have a class specifier using the same basic mechanism.
This example (LV 2009) shows how useful this could be. You don't need anything installed. Just run the VI and start changing properties.
Caveats:
It will only work on the last property in the node.
It doesn't have the proper list of names and it doesn't implement all the features in the idea, as this is just a basic example.
Note - this is similar to this idea, but I think that it's much more usable. Also note that the second idea refers to a QDKS which ships with 2010, but that is far from perfect.

Here's a more detailed response.
Browser:
Click Ctrl+Shift+B.
Get a new window. Great. Just lost a little bit of focus on what I was doing.
Find the search button. Oh, there it is. It's that little button.
Oh, another window popped up. What did I want? ... ... ... Ah, yes. It was that property.
Search for it. OK, that was easy. Now Enter.
Oh, I'm back to the original browser window, but the property is highlighted.
OK, so now I can drag the property into the BD and get a new property node with that property, but that's not actually what I wanted. I wanted to set a property on an existing node.
So, to summarize: A key combo, some mouse activity, 3 window changes and we still didn't get what we want.
Compare that to:
Ctrl+Click on the property you want to replace.
Start typing.
The intellisense popup appears as part of the current window, already navigable with the up and down keys.
Press Enter.
And two additional points:
Imagine working in VS without intellisense. What if you had to use something similar to the browser (or the menu hierarchy) every single time you wanted to get a property?
You encourage people to work with LV classes. Property nodes offer a productivity enhancement when working with classes and this offers another one, so you not only not be questioning it. You should be evangalizing it.
And for those who survived this far, a bonus. This example (LV 2009) shows how useful this could be. You don't need anything installed. Just run the VI and start changing properties.
Caveats:
It will only work on the last property in the node.
It doesn't have the proper list of names and it doesn't implement all the features in the idea, as this is just a basic example.

What is difference between local variable and property node ?

What is difference between local variable and property node ?
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To make things clear, here are two small examples that show how nasty locals and value properties can be to the naive programmer.
- Open the diagram of the race condition.vi before running it and try to predict what will be the values of the two counters after the third run.
- Use the Compare Locals Properties and Wires.vi to find out how slow locals and value properties can be (times 1000+).
This being demonstrated, I must add that I use globals and value properties quite often, because they are often very convenient
Chilly Charly (aka CC)
E-List Master - Kudos glutton - Press the yellow button on the left...
Attachments:
Race condition.vi ‏9 KB
Compare Locals Properties and Wires.vi ‏18 KB

Is there a way to reference the property node value of a control in another VI?

Let's say that I have a situation like the one shown in the attached image.
I have an interlock system which is basically a bunch of booleans
If for example the "RF Enable" button in the "interlock VI" is true, then I should be able to flick the ON switch in my other VI (in the back), but if the value is FALSE, then it shouldn't allow it.
In other words, how do I check the value of a control across 2 separate VIs (running simultaneously)?
Thanks!!
Attachments:
sample.jpg ‏295 KB

Is one VI launched by the other, or are they launched independently? If it's the former then you just need to pass the control reference to the subVI via terminal node. If it's the latter there are a variety of ways to handle this:
Use a global variable - somewhat "sloppy" as it requires a global variable, and can lead to race conditions. In the "Interlock" VI you just set the value of the global variable when you change the value of the Boolean. In the other you're just reading it.
Action Engine - Ben wrote a Community Nugget a while back. Similar concept to a global variable.
Queue - The "Interlock" VI simply pops an element onto the queue with the value. The other VI just monitors the queue for a new element. It just needs to have something like a shift register to keep track of the last state.
Use the VI Server to access the controls of the "Interlock" VI. You can do this by accessing the "Interlock" VI's pane and get the control references. With the control reference you just need to get the value with a property node.
... (I'll let others chime in)

Just checking on another odd feature: Typedef enum Property Node "Value" not reflecting changes in the Typedef?

Just encountered this odd behavior in LV 2011 which I reduced to the following example:
- create a new VI and drop an enum control on te FP.
- make this control a typedef and open the corresponding typedef
- create a "case 1" item and a "case 2" item
- save the typedef (I used the name Typedef Control 1) and CLOSE it (this is to allow updating of the original control).
- drop a case structure on the diagram and connect the enum to it:
So far so good. Now create a "Value" Property node for the enum and use it instead of the terminal:
If I now go back to the typedef and add a "case 3" item, save the typedef and close it, the control is updated, but the Property node is not.
How do I know that? For one, the Case Structure contextual menu does not offer to create a case for every value. Also, if I add a "case 3" case manually, it turns red.
Luckily, the magic Ctrl-R key stroke actually does solve this problem.
Tested in LV 2011.

By Ctrl-R trick do you simply mean running the VI? That is one way to force a recompile, but if you hold down Ctrl while pressing the run button you can recompile without running. This should not be "dangerous" in any situation.
As you have drawn your example, I see no reason not to use a local in that situation (ok, maybe for vanity). Still, I view the behavior you describe as a bug, and it should certainly be fixed for the benefit of local haters out there. You have to be a little careful where you draw the line between what gets handled in real time and what gets handled only at compile time.

Invoke, property nodes

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