Visual Basic

2-May-05 21:05

I am using IDisposable interface and trying to dispose my class but that not working. Class variables still hold references to old values. How can i actually dispose off the class. I was of the view that by disposing off a class all the managed memory is freed up.

Public Overloads Sub Dispose() Implements System.IDisposable.Dispose
Dispose(True)
GC.SuppressFinalize(Me)
End Sub

Colin Angus Mackay3-May-05 1:07

3-May-05 1:07

The Dispose method is there so you can free up UNmanaged resources that the class uses, it will not affect any references to the class. You should only call dispose when nothing is referencing your class any more because they could potentially call a method that will not work as the unmanaged resources have been freed.

Does this help?

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nitin_ion3-May-05 1:25

3-May-05 1:25

This is the way i am using the references

Public Class Class3
Private strH3 As String

Public Sub dispose()
GC.Collect()
End Sub

Public Property H3() As String
Get
Return strH3
End Get
Set(ByVal Value As String)
strH3 = Value
End Set
End Property

End Class

Public Class Class1

Dim c3 As Class3 = New Class3

Public Sub H3()
c3.H3 = "Class3 => Class1"
MsgBox(c3.H3)
c3.dispose()
End Sub

Public Sub dispose()
GC.Collect()
End Sub
End Class

Form_Load event of the application

Dim a As Class1 = New Class1

a.H3()
a.dispose()
GC.Collect()

a.H3()

Now when i call the c3.dispose in class1 then the reference to tclass3 should be removed and later when i call a3.dispose reference to a class1 will be destroyed. Second call to a.h3 works fine as well.

I have tried the finalize method as well but the result is same

now when i set a=nothing then it works fine but we know that nothing sets it to the default value. so if i have a constructor with some default values it will set it to that.

If i am wrong do correct it.

Colin Angus Mackay3-May-05 1:36

3-May-05 1:36

First, you should not be calling GC.Collect() - the garbage collector is optimised already so don't undo that optimisation by forcing a collect.

You don't appear to have any UNmanaged resources so the dispose method is pointless - it is for disposing of unmanged (non-.NET) resources. If you don't directly have any unmanaged resources in your class, but it is made up of object that have dispose methods, then your dispose method should call dispose on these objects. So, there are only 2 valid reasons for having a Dispose method. (1) Clear up unmanaged resources, (2) calling dispose on objects in the class.

nitin_ten wrote:
Now when i call the c3.dispose in class1 then the reference to tclass3 should be removed

No, as I've said already, that is not how it works. Dispose is only for clearing up unmanaged resources. It does NOT remove references.

nitin_ten wrote:
now when i set a=nothing then it works fine but we know that nothing sets it to the default value

No, that is not correct. If you set a reference to Nothing the reference does not point to anything. It does not create a default instance of the class; it does not initialise any values.

Does this help?

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nitin_ion3-May-05 1:48

3-May-05 1:48

thanks for this, but my problem is still the same how do i destroy the object completely. Nothing won't work and dispose as u said won't work either and even though gc.collect should work but i want to refrain myself from using it and .net doesn't have 'deterministic finalization'. so what is the solution.

Colin Angus Mackay3-May-05 3:24

3-May-05 3:24

When you set all references to the object to Nothing it is effectively destroyed. While it does still reside in memory for a while, until the garbage collector gets it, it is no longer accessible because nothing refernces it.

If you have a reference to an object then the garbage collector cannot collect it because something is referencing it. If something is referencing it then it is not safe to remove it.

What you might consider looking into is the WeakReference[^] class. This allows you to hold a reference to an object that the garbage collector effectively ignores. So, if you remove all strong references (i.e. a normal reference) then the garbage collector will remove it when it gets round to it. The weak reference will then return Nothing.

Does this help?

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nitin_ion3-May-05 19:21

3-May-05 19:21

Thanx Colin. I first set all the reference of class3 in class1 to nothing and then set the reference of class1 to nothing and then called

GC.GetTotalMemory(True)
GC.Collect()
GC.GetTotalMemory(True)

the memory is freed up and the object is destroyed. The problem i found out in the application is that i am using collections and even though when i set the object of the class to nothing collection should also freeup the memory allocation. But that is what is not happening. I found out that on the click event of the button when i create a new object of the class, all the variable except the collection are re initialized to their default value. In case of collection they already have old values and are adding new values along with the old one. What is the problem.

Colin Angus Mackay3-May-05 20:46

3-May-05 20:46

Since I don't know anything about this collection I cannot really say. If the collection is a member variable on your form and you have not deleted the contents then of course the values will be retained so long as the form exists. The collection will be holding references to the objects, and since the object has a reference to it the garbage collector won't touch it.

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nitin_ion3-May-05 20:51

3-May-05 20:51

I forgot to mention that collection is declared as shared and i did figured out that this is the problem. But i cannot declare collection as instance of the class. But i want to destroy the collection with the instance of the class. so i tried c.col =nothing (col is collection type property). But the next time i click on the button it gives object reference error whcih is understandable since shared are not instance specific. So the now the class is initialized but the shared collection is already set to nothing.
What should i do so that the collection is destroyed along with the instance of the class or is there a datatype that works like shared but is destroyed when the instance is destroyed.

Collection is declared in the declaration part.

Colin Angus Mackay3-May-05 22:28

3-May-05 22:28

I don't understand why the collection is shared. If you want to destroy the shared collection with an instance of the class (i.e. any instance of the class) then it would affect all instances of the class.

Have you considered just emptying the collection? Or assigning a new collection object to the shared member variable. You could encapsulate this by creating, say, a Reset() method that either empties the collection, or assigns a new collection to the shared member variable. This would mean that there is at least a collection object, even if it doesn't have any items in it.

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nitin_ion3-May-05 22:59