CODEWITHSUNDEEP
c#datetimecastingnull
user1017882
user1017882

Reputation:

Casting an object which could be null

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?

Upvotes: 3

Views: 5781

Answers (4)

Henk Holterman
Henk Holterman

Reputation: 273439

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.

Upvotes: 4

Ebad Masood
Ebad Masood

Reputation: 2379

Try using Array.ConvertAll method. Below is roughly how it is implemented:

DateTime?[] dates = Array.ConvertAll<object, DateTime?>arrayOfObjects,DateTime);

Note: This is just a rough idea. you can correct it to suit your self.

Upvotes: -1

Roland Mai
Roland Mai

Reputation: 31097

A better approach would be to do something like:

if(arrayOfObjects[dateObject] != null && arrayOfObjects[dateObject] is DateTime)
{
  DateTime testDate = (DateTime)arrayOfObjects[dateObject];
  // logic here
}

or something like:

DateTime? testDate = null;
if(arrayOfObjects[dateObject] is DateTime)
{
    testDate = (DateTime)arrayOfObjects[dateObject];
} 
else if (arrayOfObjects[dateObject] is Nullable<DateTime>) 
{
    testDate = (Nullable<DateTime>)arrayOfObjects[dateObject];
}

Upvotes: 0

Ivan Nikitin
Ivan Nikitin

Reputation: 4143

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];

Upvotes: 2

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