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”);