Question

I got a requirement in my project to add another property to some class.
Now I want to avoid changing the class because I figured it shouldn’t be aware that he has this property (this property only has significance in the context of this project).

The way I thought to accomplish this was (Please critic this because I wanna know if there are simpler ways of doing this)

1. Adding a new singleton class that has a mapping between objects of my class and the type of the property I wanted to add
2. adding in this class an extension method (extension property?) to access the mapping and fetch the property.

Is there a simpler alternative?
Is this just unnecessary complexity? Maybe I should just add a new property to my class?

Thanks!

Answer 1

The design you’ve described is actually the one used by Microsoft to implement the DependencyProperty system and, in particular, Attached Properties, though in the greater context of a binding framework. That said, using a dictionary with ‘attached’ data is a very typical solution when you need to tag a class with additional context for a particular use, but don’t want to modify the class.