并且也是用法

' Sometimes we don't need to evaluate all the conditions in an if statement's boolean check.

' Let's suppose we have a list of strings:

Dim MyCollection as List(Of String) = New List(of String)()

' We want to evaluate the first value inside our list:

If MyCollection.Count > 0 And MyCollection(0).Equals("Somevalue")
    Console.WriteLine("Yes, I've found Somevalue in the collection!")
End If 

' If MyCollection is empty, an exception will be thrown at runtime.
' This because it evaluates both first and second condition of the 
' if statement regardless of the outcome of the first condition.

' Now let's apply the AndAlso operator

If MyCollection.Count > 0 AndAlso MyCollection(0).Equals("Somevalue")
    Console.WriteLine("Yes, I've found Somevalue in the collection!")
End If 

' This won't throw any exception because the compiler evaluates just the first condition.
' If the first condition returns False, the second expression isn't evaluated at all.