Formulas in Revit Family Do Not Lock

[jmiller]

This appears to be a bug in the family editor at least as far back as Revit 2011.  When using a formula to drive a parameter, the value for the parameter should turn gray and not be editable by the user in the project environment.  At least, that's the theory that seems to be espoused in the manual.  What I've come to determine is that this behavior is true for formulas that include 'if' or other statements, and for simple math that uses two or more parameter names ("Parameter 1 + Parameter 2").  However, formulas that include only one parameter name plus a value ("Parameter 1 + 1'") have inconsistent behavior.  Sometimes the parameter value will turn gray, and sometimes it stays black.  It calculates correctly, but the user has no way in the project environment to tell that the value is being calculated by a formula and is free to type a different value into the field.  I have searched all over and can find no mention of this behavior anywhere.  Am I truly the only person having this problem over the last 5 years?

Some examples:

Expected behavior:

Observed behavior:

And yet, sometimes the same type of expression works as expected:

???

[L.Maas · Accepted solution]

Not really noticed when using. Could be that when simple parameters are used Revit can still work with it.

As an example:

B = A + 1. In this case even if there is a formula for Parameter B. When changing B Revit knows what A should be and can update both values.

This situation changes when the formula is something like B = A + C + 1. Then no conclusion can be drawn about A or C when B changes.

I see that behaviour changes when parameters are type parameters (not greyed) vs instance parameters (greyed).

As mentioned never really noticed this behaviour, so never bothered me. So I would not call it a real bug but at most and inconsistent policy.

In case you would like to see this behaviour changed you could ask by using THIS form on the Autodesk Website.

[fabiosato]

There is an workaround to prevent editing the input parameter from the output one, use a formula like:

B=if(1=1,A+1,1), actually the last value has no meaning.

This will make possible to edit only the A parameter

[jmiller]

Thanks. I'll use the form to request that the behavior be made consistent. It's really irritating because content we build in house gets corrupted in the project environment because users can't tell which parameters are being calculated by formulas (and so they change the values...). And no, in my experience Revit does not automatically compensate for the change in value to make everything still stay the same.

Jeff Miller LEED AP, CTS-D
Senior Consultant

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