二次开发中建立UDF的过程
Create a new UDF instantiation in the current part. The steps to instantiate a new UDF are as follows:
1) Open the UDF definition file using UF_PART_open_quiet().
2) Find the UDF feature definition.
3) Ask for the UDF definition to get all the external references.
4) Change part to the instantiation part
5) For each external reference you need to select a new reference in the
instantiation part.
6) Get new values for the expressions.
7) Use UF_MODL_create_instantiated_udf to create a UDF instantiation.