RVTDocs.com
Namespace: Autodesk.Revit.DB Class: FamilyInstance

FamilyInstance.HostParameter

Property
Description:
If the instance is hosted by a wall, this property returns the parameter value of the insertion point of the instance along the wall's location curve, as long as the family of the instance isn't work plane based.
Remarks:
This works for instances with a host element that is of type Wall or is in the OST_Walls category only, including in-place ones.
Syntax
public double HostParameter { get; }
Exceptions
Exception Condition
InvalidOperationException Only hosted instances whose family is not work plane based can support this functionality.
InvalidOperationException Only hosted instances of type Wall or in-place elements of category OST_Walls can support this functionality.