I've just started to work with FxCop to see how poorly my code does against its full set of rules. I'm starting off with the "Breaking" rules, and the first one I came across was CA2227, which basically says that you should make a collection property's setter readonly, so that you can't accidentally change the collection data.

Since I'm using MVVM, I've found it very convenient to use an ObservableCollection with get/set properties because it makes my GUI updates easy and concise in the code-behind. However, I can also see what FxCop is complaining about.

Another situation that I just ran into is with WF, where I need to set the parameters when creating the workflow, and I'd hate to have to write a wrapper class around the collection I'm using just to avoid this particular error message.

For example, here's a sample runtime error message that I get when I make properties readonly:

The activity 'MyWorkflow' has no public writable property named 'MyCollectionOfStuff'

What are you opinions on this? I could either ignore this particular error, but that's probably not good because I could conceivably violate this rule elsewhere in the code where MVVM doesn't apply (model only code, for example). I think I could also change it from a property to a class with methods to manipulate the underlying collection, and then raise the necessary notification from the setter method. I'm a little confused... can anyone shed some light on this?