How do I determine an array's dimension from the following IDL?

[Ray Stevens]

I have an IDL defined as follows:

[SendAs(IdlType.A, Length=78f, Dim=20f, Trim=true)]public StringBuilder[]
LEGAL_FREEFORM ;

In this case it is obvious that the Dim is 20 with a length of 78, however I
want to be able to determine this at run time.

This compiles but fails at runtime because it is not set to an instance of
the object:

int itr = inrec.LEGAL_FREEFORM.GetLength(0);

I would like to determine both the dimension and length parameters (i.e., 20
and 78) inso far as I have potentially large StringBuilder objects that will
need to be chunked into this array prior to sending it to the mainframe.