MyBase.Dispose: NullReferenceException was unhandled

[Martin H.]

Hi,

I've got this problem:

I currently work on a control which inherits from ListBox.
In my control I shadowed the Items with a custom ObjectCollection, which
has some additional properties.

Now, this happens:
If I add some entries to my control, click on one of the items and then
close the form with the control on it, I get this error message:

NullReferenceException was unhandled
Object reference not set to an instance of an object

The error occurs in the form's Dispose method at MyBase.Dispose.

'Form overrides dispose to clean up the component list.
Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
If disposing Then
If Not (components Is Nothing) Then
components.Dispose()
End If
End If
MyBase.Dispose(disposing)
End Sub


I have no clue how to identify the problem, especially since I can
deactivate the click routine and the error still occurs...

Any ideas what the problem could be?

Thanks a lot in advance!

Best regards,

Martin

 

[Cor Ligthert [MVP]]

Matt,

What do you have in the disposing from the by you derived Listbox

Cor

 

[Martin H.]

Hello Cor,

What do you have in the disposing from the by you derived Listbox

I did not write any code for disposing my custom listbox.

Best regards,

Martin

 

[Brian Gideon]

Hi,

I've got this problem:

I currently work on a control which inherits from ListBox.
In my control I shadowed the Items with a custom ObjectCollection, which
has some additional properties.

Now, this happens:
If I add some entries to my control, click on one of the items and then
close the form with the control on it, I get this error message:

NullReferenceException was unhandled
Object reference not set to an instance of an object

The error occurs in the form's Dispose method at MyBase.Dispose.

'Form overrides dispose to clean up the component list.
Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
If disposing Then
If Not (components Is Nothing) Then
components.Dispose()
End If
End If
MyBase.Dispose(disposing)
End Sub

I have no clue how to identify the problem, especially since I can
deactivate the click routine and the error still occurs...

Any ideas what the problem could be?

Thanks a lot in advance!

Best regards,

Martin

Hi,

Can you post a short, but complete program demonstrating the problem?

Brian

 

[Martin H.]

Hello Brian,

Can you post a short, but complete program demonstrating the problem?

You can download the test project from
http://www.henke-hk.com/download/DisposeProblem.zip

Thanks in advance.

Happy holidays!

Martin

 

[Martin H.]

Hi everybody,

I've got the problem solved. It occurred, because I did not add any
items to the base class.

Thanks to all for your help.

Best regards,

Martin