check string for nothing and then for certain value in 1 line?

Question

I always seem to see if a string (querystring value usually) has a value but first I have to check that it is not nothing first so I end up with 2 if then statements - am I missing somethign here - there has to be a better way to do this:

If Not String.IsNullOrEmpty(myString) Then
  If CBool(myString) Then
   //code
   End If
End If

Answer 1

The boolean "and" operator in your language of choice? Conditionals generally short-circuit so if the first one fails, the second won't run/error.

Answer 2

The problem with that is I get an Invalid Cast Exception because myString is nothing when the Cbool is applied, here is the error:

Conversion from string "" to type 'Boolean' is not valid.

Answer 3

In VB.Net, And does not short-circuit, but AndAlso does.

(same for Or and OrElse)

So your code should look something like

If Not String.IsNullOrEmpty(myString) AndAlso CBool(myString) Then 
    ....
End If

Answer 4

FYI this type of code fits perfect as an "extension method". In short this means that you can extend string with a method providing your own code.

Look it up :)

Answer 5

AndAlso (as mentioned) is the most general purpose answer. But, you could also use the various TryParse methods, which will make code like this:

Dim b as Boolean
If Boolean.TryParse(myString, b) AndAlso b Then
End If

Bonus, it'll save you from the FormatException when someone sends in "blah" in your querystring.

Answer 6

Use the following if using .NET 2.0 or greater: String.IsNullOrEmpty(thestringobject)

Will evaluate to True or False depending. I usually create another function in a Utility Class that does this check and also checks the trim/length so I know if the string object is null, empty, or a bunch of blanks.