Question

I Have a control inheriting the dataGridView control.
I have the onLostFocus method overrided. Lately I encountereda weird behavior. if trying to close the form while a cell is in teh middle of being edited. the dispose method will be called and then teh onLostFocus is called that results in a nullReferenceException

   protected override void OnLostFocus(EventArgs e)
        {
           base.OnLostFocus(e);
          base.DefaultCellStyle = myStyle1;
            }
        } 

my question is how come the lostFocus is called after the userControl starts being disposed?
and what is the correct way to handle this isuue?
A workaround can be to check explicitly if dispose had started and then return from the OnLostFocus. But I’d rather understans better what happens behind.
Thanks!

Answer 1

According to http://msdn.microsoft.com/en-us/library/system.windows.forms.control.lostfocus.aspx, Microsoft suggested that OnEnter and OnLeave should be used instead of OnGotFocus and OnLostFocus.

The GotFocus and LostFocus events are
low-level focus events that are tied
to the WM_KILLFOCUS and WM_SETFOCUS
Windows messages. Typically, the
GotFocus and LostFocus events are only
used when updating UICues or when
writing custom controls. Instead the
Enter and Leave events should be used
for all controls except the Form
class, which uses the Activated and
Deactivate events. For more
information about the GotFocus and
LostFocus events, see the WM_SETFOCUS
and WM_KILLFOCUS topics in the
“Keyboard Input Reference” section in
the MSDN library at
http://msdn.microsoft.com/library.http://msdn.microsoft.com/library.