.NET Tips and Tricks

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New in Visual C# 6.0, Visual Basic 14: New Null/Nothing Check

I don't know how many times I've written this code like this:

if (stringVariable != null)
{
  int x = stringVariable.Length;
}

In Visual Basic I'd write this:

If stringVariable IsNot Nothing then
  Dim x as Integer 
  x = stringVariable.Length
End If

I test the string for null/nothing because if I try to get the Length of a variable set to null/Nothing ... well, I don't get the string's Length (null values don't have lengths). Instead, I get an exception.

To simplify this block of code, both C# 6.0 and Visual Basic 14 add a new operator that you can tack onto the end of a string (or other values): the question mark (?). If the string that the operator is added to is null then the expression returns null and no further processing happens.

This means that I could rewrite my previous code like this:

int x = stringVariable?.Length;

If stringVariable is set to null or Nothing, processing ends at the ? mark and no attempt is made to retrieve the Length value ... which means no exception is raised.

However, my code still isn't right because, after all, the expression with the ? operator has to return something. If my string is null then the ? operator will return null ... and my code has to handle that. The solution is to use a nullable data type to catch the result of my expression. For my example, the final code looks like this:

Dim x As Integer? = stringVariable?.Length

Two other items: First, you can use the ? operator with types other than strings. Second, if you think the ? operator is useful, consider looking at the string object's IsNullOrWhiteSpace method.

Posted by Peter Vogel on 05/04/2015 at 11:05 AM


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