Interface attributes not automatically replicated to class in UML class diagram in Visual Studio

Question

In Visual Studio, I've created a UML class diagram with a class that realises an interface containing an attribute and an operation as thus:

The operation is automatically replicated to the class, but not the attribute. The MSDN guidelines indicate this behaviour:

When you create a realization connector, the operations of the interface are automatically replicated in the realizing class. If you add new operations to an interface, they are replicated in its realizing classes.

However, this seems counterintuitive to their statement just beforehand, namely:

Realization means that a class implements the attributes and operations specified by the interface.

I'm sure there must be a good technical reason for this (some OO concept like polymorphism or abstraction), but I can't think why it discerns between attributes and operations in this way.

Can anyone give me some insight into this, and perhaps what I should do to get round it (do I add the attributes to the class manually in UML?), as it's resulting in generated code that doesn't compile?

Answer 1

While I don't know for sure, I'd imagine it is because in C# interfaces cannot contain fields, only methods. Having attributes on an Interface therefore doesn't make sense.

Interfaces can contain properties, but these just get compiled to PropType get_PropName() and void set_PropName(PropType value) . (Fun fact, trying to declare those methods yourself will generate a compiler error.)

Unfortunately, there is not a nice "out of the box" way of defining properties in UML class diagrams, as they are a language specific feature. I think you have to define a custom stereotype and the templates to generate the code accordingly - faff.