Question

Somewhat unclear to me are references (pointers?) to classes in VB.NET. The question I am about to ask can be answered by a little bit of testing, but I was wondering if anybody could post a decent explanation (or links, too).

If you create a class:

Public Class ReferenceClass      Private myBooleanValue As Boolean = False     Public Property BooleanValue As Boolean         Get             Return myBooleanValue         End Get         Set(value As Boolean)             myBooleanValue = value         End Set     End Property  End Class 

And then a class which actually uses this class as a property:

Public Class UsingClass       Private myReference As ReferenceClass      Public Property Reference As ReferenceClass         Get              return myReference          End Get          Set(value As ReferenceClass)              myReference = value          End Set      End Property       Public Sub New(ByVal Reference As ReferenceClass)          myReference = Reference      End Sub  End Class 

And then use it like this:

Public Class RuntimeOrSomething       Public Shared myReference As ReferenceClass      Public Shared ReadOnly Property Reference As ReferenceClass          Get              If myReference Is Nothing Then myReference = new ReferenceClass()              return myReference          End Get      End Property       Public Shared Function BooleanCheck() As Boolean          Reference.BooleanValue = True          Dim tempClass As New UsingClass(Reference)          tempClass.Reference.BooleanValue = False           Return (tempClass.Reference.BooleanValue = Reference.BooleanValue)      End Sub       Public Shared Sub DoNothing()           Reference.BooleanValue = True           Dim someBoolean As Boolean = BooleanCheck            ' Now Reference.Booleanvalue is 'False'      End Sub  End Class 

Now the function BooleanCheck will always return true, even though the reference is passed to the new class UsingClass ‘by value’, not by reference. So a copy of the class is not made, but the local variable myReference in UsingClass still references/points to the property Reference in RuntimeOrSomething.

How can this be explained elegantly?

Answer 1

A reference points to an instance of an object, it is not an instance of an object. Making a copy of the directions to the object does not create another object, it creates another reference that also points to the same object.