Is the class
part of the same assembly? If yes, then just create an object of it and you can access the property using the object. Something luke this -
TwoClass objTwoClass = new TwoClass();
int ValueOfA = objTwoClass.A;
objTwoClass.A = 1;
I didn't get this point in your question - "The problem is TwoClass cannot inherit from OneClass."? AFAIK, the partial classes can be inherited.