>I saw this AndAlso usage in such a line:
>
>

>            If (requestValidationSource__1 = RequestValidationSource.QueryString) AndAlso (collectionKey = "data") Then
>

>
>What is the difference with And?

(1) And - http://msdn.microsoft.com/en-us/library/sdbcfyzh.aspx
Evaluatates all expressions, you can use side-effects

If ( ( x   > 1) And MyFunction()) )

MyFunction() will be called regardless of whether x > 1 or not

(2) AndAlso - http://msdn.microsoft.com/en-us/library/cb8x3kfz.aspx


Is said to use short-circuiting and stops evaluating as soon as it finds that it has processed sufficient parts of the expression to know the result

If ( ( x  > 1) AndAlso MyFunction()) )

if x less or equal to 1, then MyFunction() will not be called