I have a class (sharedClass) that is instantiated (not derived) by two other
classes (guiClassA and guiClassB).  The sharedClass needs to be able to call
a method that is defined in its parent class (guiClass).  

Specifically, when guiClassA or guiClassB calls a method from the
sharedClass, the sharedClass needs to log its actions by sending strings to
the guiClass (via guiClass method calls), which in turn display or record
this log information in their own unique ways.  

How can the sharedClass call out a function from its parent class without
knowing exactly what kind of class the parent class is?  (I can however
guarantee that the parent class will implement the logging function).

Since both guiClasses are not used in the same application, I was able to
solve this  in C++ by declaring the logging function prototype in a header
file that was included by all the classes, and then defining the function
implementation at the same level as the guiClass was instantiated.  Thus, the
connection was made by the linker.  Is there any way to do something similar
in C#?