Why do I get "A first chance exception of type 'System.ArgumentException' occurred in mscorlib.dll" exception

Posted on 2008-06-25
Last Modified: 2008-06-25
Hi guy,
I'm a bit puzzled as to why I'm getting a "A first chance exception ..." when trying to remove an event handler using "RemoveHandler". I this particular case I have five (5) RemoveHandler statments looking identical, but with different parameters, and only the last statement fails.

The app appears to be working fine so I'm just a bit confused.

Any thoughts?

Question by:gem56
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LVL 96

Expert Comment

by:Bob Learned
ID: 21866732
There are too many possibilities to be sure of anything, without more detail.

Author Comment

ID: 21866990
As part of creating a Form instance I added several event handlers that includes the following statement:
   "AddHandler Me.ParentSection.Panel.Click, AddressOf Me.Sections.ParentForm.DeselectAllSectionsClick"

Then as part of closing that Form I am removing the added event handlers amongst which is the following statement that compliments the AddHandler statement above:
   "RemoveHandler Me.ParentSection.Panel.Click, AddressOf Me.Sections.ParentForm.DeselectAllSectionsClick"

So I wasn't expecting any exceptions because stepping through the code I can't see any empty pointers, etc. so I'm a bit confused.

LVL 96

Expert Comment

by:Bob Learned
ID: 21868144

Do you have the full stack trace text for the exception?  When the form is closed, is it disposed?
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Author Comment

ID: 21868840
Sorry, I forgot to say that I get that message only in the IDE Immediate Window and not as a crash.
The Form also closes OK and all looks normal, except for those messages so I was just curious as to whether I should worry about that or not.


LVL 96

Accepted Solution

Bob Learned earned 250 total points
ID: 21869952
I would ignore that exception with a Try/Catch block.

Author Comment

ID: 21870670
Actually I am using Try/Catch but (stupid me) I forgot to print the ex.Message from the "Catch ex As Exception", I only looked at the output in Immediate Window.

The message in (Catch ex As Exception) has the following message:
"Delegate to an instance method cannot have null 'This'."

That makes sense so, even though I expected all references to be valid, sometimes "Me.Sections.ParentForm' is Nothing and hence the failure.

Thanks for your assistance (as always).


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