Shared Parameters and Multi-Category | Auto update

[jejeno2544]

Hi all, 

I'm creating an add-in that adds annotation labels to pipes, ducts, etc. 
And I need to display the length of these elements. 
I know that I can create separate annotations for each type (pipe, duct, ...):

As a result, I get a lot of files.

But I want to have one common Multi-Category tag.
I've created a custom shared parameter and set the name to CustomLength. 

The problem is that I need to manually set this parameter, and when I resize the pipe, this value is not updated automatically. 

Is there a way to create a Multi-Category - CustomLength tag that takes the information from the Length element and automatically updates if we make any changes to that element?

Thanks for any ideas.

[jeremy_tammik]

You should explore how to achieve what you need manually in the end user interface first. The API will almost never provide any functionality beyond that.

One little API artefact that I found is the PostableCommand enumeration member:

MultiCategoryTag

Attaches tags to elements of multiple categories, based on a shared parameter.

https://www.revitapidocs.com/2023/f6ccdc1b-6ac3-9c49-d0bb-8a7d1877eab0.htm

It mentions a shared parameter that apparently plays some role in the multi-category tagging.

[ricaun]

IUpdater works perfectly for this case.

For example, every time an element with the types Pipe, Duct, and Conduit is created or modified a code runs to update the CustomLength parameter using the build-in Length of the element.

• https://help.autodesk.com/view/RVT/2021/ENU/?guid=Revit_API_Revit_API_Developers_Guide_Advanced_Topi...