What exception should be thrown when validating results from external callbacks in .NET?

Question

ArgumentException and ArgumentNullException are both used for validating arguments, eg.

if (argument == null)
    throw new ArgumentNullException("argument must not be null", "argument");

What is the best equivalent for validating the results of callbacks, eg.

var x = argument.GetX();
if (x == null)
    throw ???

Answer 1

Hi there.

I personally use ArgumentException or ArgumentNullException in conjunction with testing parameters passed to routines, like this:

Public Sub Test(s As Object)

If s Is Nothing Then
  Throw New ArgumentNullException("s")
End If

End Sub

In your case, I would just throw a normal Exception, since the variable 'x' is not an argument passed to your routine, it's a local variable. I would recommend using ArgumentException or ArgumentNullException for parameters passed to routines rather then local variables.

Cheers. Jas.

Answer 2

Without knowing much about your code, I can suggest throwing InvalidOperationException.

Alternatively, if this piece of code is important, you can create custom exception, say XLoadException, and throw that.