How can I make a class variable accessible from different object instances of the same class?

You may have the need to be able to access the same instance of a class variable from multiple object instances of that class. This is known as a "class" scope variable. Here I'll explain how it's done.
There is an important destinction between the scopes of member variables in a class. Under normal circumstances, the variables you put into your class are known as "instance" variables. You can modify any of these variables and make them "class" scope by putting the word static [C#] or Shared [VB] after the first scope modifier keyword.

Public Class MyClass
	Public Shared AStaticStr As String
End Class
Being class scope means that from the time the class is loaded into the runtime, that variables is alive. Any instance of that class can access that variable (assuming it's either Public or Protected, but not Private).

Dim objMyClass1 As New MyClass
Dim objMyClass2 As New MyClass

objMyClass1.AStaticStr = "Hello"
Print objMyClass2.AStaticStr 'Prints "Hello"
objMyClass2.AStaticStr = "World"
Print objMyClass1.AStaticStr 'Prints "World"
If you inherit from that class you'll be able to see the same instance of that variable from within any instance of your derived classes.

Public Class MySubClass
	Inherits MyClass
	Public Function AMethod() As String
		Return AStaticStr
	End Sub
End Class
You can make any member (variables, properties, methods, etc) of a class Shared but you have to remember that Shared methods can only access other Shared members of the class. They can not access instance scope members. However, any instance scope member can access Shared members.

Where to Next?

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Doc ID 272
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Written by Imar Spaanjaars
Date Posted 04/14/2004 22:52
Date Last Reviewed 08/06/2006 16:54

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