Adding a parameter through code

[Anonymous]

I have this code

        public void CreateParameter(ExternalCommandData commandData) {
         UIApplication uiapp = commandData.Application;
         UIDocument uidoc = uiapp.ActiveUIDocument;
         Document doc = uidoc.Document;
         FamilyManager fam = doc.FamilyManager;
         var param = fam.AddParameter("Size", BuiltInParameterGroup.PG_STRUCTURAL, ParameterType.Length, true);
         fam.Set(param, 0.2);
         }

Although I can't seen to run it in the Macro Manager --> http://i.imgur.com/1iaApXy.png

I've also tried running it as an Add-Ins External Tools and this message pops up --> http://i.imgur.com/ZIKpC8i.png

I'm new to Revit API so I'm not sure what I need to do to fix this. Any help would be great.

[keith_white · Accepted solution]

You need to separate the parameter creation and the parameter value update into two transactions.

First create the parameter in a transaction and commit it.

var param = fam.AddParameter("Size", BuiltInParameterGroup.PG_STRUCTURAL, ParameterType.Length, true);

Then update the parameter in a transaction and commit it.

fam.Set(param, 0.2);