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(FooArgs args) { ... } 

The deprecated method contained a growing list of parameters. These parameters are now properties on the FooArgs class. The deprecated method has several guard conditions which checked for null values with the following structure:

if (parameter1 == null)     throw new ArgumentNullException(“parameter1”); if (parameter... == null)     throw new ArgumentNullException(“parameter...”); if (parameterN == null)     throw new ArgumentNullException(“parameterN”); 

Now that the parameters have been collapsed into the FooArgs class should I throw an ArgumentNullException for the individual properties of the FooArgs parameter:

if (args.Property1 == null)     throw new ArgumentNullException(“args.Property1”); if (args.Property... == null)     throw new ArgumentNullException(“args.Property...”); if (args.PropertyN == null)     throw new ArgumentNullException(“args.PropertyN”); 

Or to throw a more general ArgumentException for the entire FooArgs parameter:

if (args.Property1 == null)     throw new ArgumentException(“Property1 cannot be null.”, “args”); if (args.Property... == null)     throw new ArgumentException(“Property... cannot be null.”, “args”); if (args.PropertyN == null)     throw new ArgumentException(“Property2 cannot be null.”, “args”); 

Thanks!

Answer 1

You need to add a check for the args itself to be non-null. The ANE is not appropriate for individual components, so you need to use more general AE, like this:

if (args == null)     throw new ArgumentNullException(“args”); if (args.Property1 == null)     throw new ArgumentException(“Property1 cannot be null.”, “args”); if (args.Property... == null)     throw new ArgumentException(“Property... cannot be null.”, “args”); if (args.PropertyN == null)     throw new ArgumentException(“Property2 cannot be null.”, “args”); 

Answer 2

While I agree completely with dasblinkenlight's answer, you may also want to consider moving the validation for FooArgs into the FooArgs class itself. If this class is designed specifically to move arguments around, it is likely not valid for it to have null proeprties, in which case, I would allow its constructor to do its validation.