Prioritize section of IF statement

Question

I've got an IF statement that validates data.

Basically looks like this:

Dim s As String = Nothing

If s Is Nothing Or s.Length = 0 Then
    Console.WriteLine("Please enter a value")
End If

Console.Read()

I'd like to check to see if it's nothing first because if I write it this way, it throws a NullReferenceException.

I've thought of re-writing it like this:

If s Is Nothing Then
    Console.WriteLine("Please enter a value")
ElseIf s.Length = 0 Then
    Console.WriteLine("Please enter a value")
End If

But if I do this I've got the same error message twice and I believe it's less clear what my intent is.

I've also tried throwing parenthesis around the s Is Nothing clause, but it doesn't work.

Is there an elegant what to test if the object is nothing and then test a property of it?

Answer 1

.NET 2.0 introduced the OrElse keyword to do short-circuiting. What this means is that it will not evaluate the right-side of the OrElse if the left side is true. Other than that, it works exactly like Or.

The And equivalent is AndAlso, which will not evaluate the right side if the left side is false.

Dim s As String = Nothing

If s Is Nothing OrElse s.Length = 0 Then
    Console.WriteLine("Please enter a value")
End If

Console.Read()

should do what you want.

Answer 2

you can use:

if (string.IsNullOrEmpty(s))
{
//do work
}