[Bug] VI methods "Create from Data Type / Reference" clear undo history

[raphschru]

Hi fellow VI scripters,

I noticed VI methods "Create from Data Type" and "Create from Reference" clear the undo history of the target VI. As a consequence, even if the action is wrapped in an undo transaction, it can't be undone:

This is not a major concern however, as a workaround is to call the method in a temporary VI / Control instead, then copy the control / constant to the target VI:

This is quite silly since it adds unnecessary steps, and I see no reason why a direct call on the target VI couldn't be undone...

I wanted to share it here because it can be critical to maintain the undo history when implementing plugins such as right-click menus, and also in a hope that NI fixes it one day...

Attached is a benchmark demonstrating the "undoability" of the different methods. Here are the results:

Regards,

Raphaël.

[wiebe@CARYA]

This might actually explain why a lot of 'normal' LabVIEW operations clear the undo history...

[raphschru]

For your information, I have reported this bug to NI. Here is a quote from the support:

"I have opened a BUG request, here is the BUG report number #3030762. I have reported this issue to the R&D team, and they have confirmed that it is indeed a BUG. However, they are unable to provide a resolution date and to be honest, I am not confident that this BUG will be fixed within this year. However, I recommend opening a new SR referencing this BUG number to check whether the issue is resolved in future LabVIEW releases."

[styrum]

The workaround with creating a temporary file is quite a big overhead.

But there is more: Not only they clear the Undo history, they also totally ignore the Position and Style inputs (they will create a control even if you explicitly tell them to create an indicator)! You have to add an additional property node call to write to the Position property(ies) to move the control and its terminal where you really want them to be and change to an indicator if needed. Looks like somebody at NI just really wanted to go home early that day when they were working on these.🙄

[raphschru]

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@styrum wrote:

[...] Not only they clear the Undo history, they also totally ignore the Position and Style inputs (they will create a control even if you explicitly tell them to create an indicator)! You have to add an additional property node call to write to the Position property(ies) to move the control and its terminal where you really want them to be and change to an indicator if needed. [...]

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Even if a little bit ambiguous, the documentation of the "Create from Data Type" VI method describes what you observe with the Style input:

"Creates a control or constant of the data type you specify. LabVIEW always creates a control initially, even if you configure Style to create a

constant or indicator. To change the type of the new object, use the Indicator property."

Keep in mind that for the Control class, style and data direction (aka "Indicator" property) are independent. You can perfectly have a control stylized as an LED or an indicator stylized as a toggle switch.

The ambiguous part in the documentation in my opinion is that it would imply that it creates a Control reference even when asking for a Diagram object (so, a Constant), which is factually wrong.

As for the ignored Position, I have not observed this behavior. If for example I set it to 12,12, it aligns with the first 12*12 grid square perfectly on the front panel. If you expect it to also position the associated Control Terminal on the diagram, then it doesn't, since it is an independent object.

Regards,

Raphaël.