ArgumentException vs. ArgumentNullException?

Question

I’m refactoring some code and adding a method which will replace a (soon-to-be) deprecated method. The new method has the following signature:

FooResult Foo         


        

Answer 1

In this case, it may be best to check for a null reference of the FooArgs parameter inside that method, and throw an ArgumentNullException if a null reference has been passed in. Then if other methods or sections of code use the parameters contained within the args class, they should be the ones to check this and throw exceptions as necessary. However, if your method that takes in the args class is the one to use all the arguments, then it would be better to check for valid parameters in that method, as you suggested.

Also, use ArgumentNullException only for arguments that are null references. If it's simply an invalid value (for example an empty string), then you should use the more generic ArgumentException.