The scope of a variable or
constant is the set of all code that can refer to it without qualifying its
name. A variable's scope is determined by where the variable is declared. It's
usually a good idea to make the scope of variables or constants as narrow as
possible (block scope is the narrowest). This helps conserve memory and
minimizes the chances of your code referring to the wrong item. I'll take a look
at the different kinds of scope in VB .NET here.
A block is a series of statements terminated by an End,
Else, Loop, or Next
statement, and an element declared within a block can be used only within that
block. Here's what block scope looks like in an example. In this case, I'll
declare a variable, strText in an If
statement. That variable can be used inside the If
statement's block, but not outside (VB .NET will tag
the second use here as a syntax error):
Dim intValue As Integer = 1
If intValue = 1 Then
Dim strText As String = "No worries."
System.Console.WriteLine(strText) 'Will not work!
An element declared within a procedure is not available
outside that procedure, and only the procedure that contains the declaration
can use it. Elements at this level are also called local
elements, and you declare them with the Dim or Static
Note also that if an element is declared inside a
procedure but outside any block within that procedure, the element can be
thought of as having block scope, where the block is the entire procedure.
When discussing scope, Visual Basic uses the term module
level to apply equally to modules, classes, and structures. You can
declare elements at this level by placing the declaration statement outside of
any procedure or block within the module, class, or structure.
When you make a declaration at the module level, the
accessibility you choose determines the scope. The namespace that contains the
module, class, or structure also affects the scope.
Elements for which you declare Private
accessibility are available for reference to every procedure in that module,
but not to any code in a different module. The Dim statement
at module level defaults to Private accessibility, so it
is equivalent to using the Private statement. However, you
can make the scope and accessibility more obvious by using Private.
In this example, I've declared Function1 as private to Module2,
so it's inaccessible in Module1 (VB .NET will tag Module2.Function1
below as a syntax error):
System.Console.WriteLine(Module2.Function1()) 'Will not work!
Private Function Function1() As String
Return "Hello from Visual Basic"
If you declare an element at module level using the Friend
or Public statement, it becomes available to all
procedures throughout the entire namespace in which it is declared. Note that
an element accessible in a namespace is also accessible from inside any
namespace nested inside that namespace.
If your project does not contain any namespace
statements, everything in the project is in the same namespace. In
this case, namespace scope can be thought of as procedure scope.