Casting an object which could be null

Question

DateTime? testDate = (DateTime?)arrayOfObjects[dateObject];

Does that code look ok? I attempted to use the as operator but I got the 'non-nullable' error. What I'm trying to say is that the object I'm choosing from the array is either DateTime or a null DateTime but either can be assigned to testDate.

Doesn't feel right doing it this way, I think I'm missing something obvious.

EDIT: I suppose it's the same as the way I could've adapted the as in the following way:

DateTime? testDate = arrayOfObjects[dateObject] as DateTime?;

Is either line of code the best way of handling potential nulls?

Answer 1

Is either line of code the best way of handling potential nulls?

The second form will silently result in null when the array contains something other than a DateTime. That seems a good reason to use the first.

To the basic question:

am I missing something or is this the typical (or at least an acceptable) approach

It is acceptable but a little obscure maybe, because it is 'hiding' an unboxing operation.
You could use:

DateTime? testDate = null;
if (arrayOfObjects[dateObject] != null)  
   testDate = (DateTime) arrayOfObjects[dateObject];  // no '?'

But that's verbose. And this particular problem doesn't lend itself well to the conditional operator (?:)

So I would stick with your first version.

Answer 2

DateTime? is a shorter form for another struct

Nullable<DateTime> {
    bool HasValue;
    DateTime Value;
}

You will never get this type from your DB, so the first line will never cast correctly. The database will provide you with a DateTime value stored in an object variable. Or a null (untyped).

DateTime is a struct, so "as" operator won't work for it. So, simply check for null as follows:

DateTime? testDate = arrayOfObjects[dateObject] == null ? (DateTime?) null : (DateTime)arrayOfObjects[dateObject];