Matt,

Thanks, for your quickly answering my question.
Yes, In debug mode I see that OnClick event handler is never fired if grid doesn't leave edit mode, to be more exact if e.Cancel is set to 'True' in OnDataSourceCellDataUpdating handler. But I hoped an UltraDataSource has any ability to know that something tries to close(dispose, etc) it from outside, like it happens when grid, placed on a form, being disposed during form closing(by clicking 'X' button). Actually I show my form(which I attached to this thread)as modal one from main application form  to allow the user to setup some values and then save they to the database by clicking on 'OK' button. I use OnDataSourceCellDataUpdating event to prevent cell from updating and showing some warning message in the corresponding cases. But if user would not continue to work with that form he should have ability to close form regardless of whether grid is in edit mode or not.
I found the solution that worked, but it seems it's not so good as I would like.
1)  I inherited from IMessageFilter and implemented PreFilterMessage(ref Message m)
 to know about clicking on 'Close' button.
 I store this fact in StorageForFormCloseActions.FormClosing Property.

   public bool PreFilterMessage(ref Message m)
        {
            if  (m.Msg == (int)WindowsMessages.WM_LBUTTONDOWN)
            {
                if (HWNDs.Contains(m.HWnd)) //HWNDs collection contains HWND of 'Close' button.
                {
                    StorageForFormCloseActions.FormClosing = true;// Now I know that form needs to be closed.
                    return false;
                }
                return false;
            }
            return false;
        }

2) On the OnFormLoad event handler of my dialog form I add this MessageFilter to application like this: Application.AddMessageFilter(MyMessageFilter);
And  also store Close Button's HWND to the corresponding collection.

On FormClosed event handler I removed this MessageFilter from application and reset StorageForFormCloseActions.Current.FormClosing to False.

3) Since I stored the fact about clciking on the 'Close' button to bool property I can use that in
OnDataSourceCellDataUpdating event handler:
   if (!StorageForFormCloseActions.Current.FormClosing)// If form is being closed there is no need to update cell's value.
            {
        ..........
            }
else
{
  e.cancel = true;
  // Here we can close form.
  // I use BeginInvoke for Close() method to let controls perform its actions.
}

It would be nice to receive from you comments on this.

Thanks in advance.

Alex.

'

Alex,

As I mentioned there's no way for the UltraDataSource to know that you've clicked the button since, in fact, the button was never clicked and there is nothing to indicate that the form will be closing should the click processing be fully completed.  What I had suggested was delaying performing the updates until a later time, such as if the user closes the dialog, which sesm to be what you're doing.  What confuses me, however, is why you need to cancel updating the data source; are you passing off an instance of the UltraDataSource to your dialog and then this dialog is directly updating the one shared by the main form?  If this is the case, I understand why you're cancelling the updates, but otherwise why bother preventing the cell from being updated if you have an OK button that will save everything that the user did?

I'm not sure what side effects implementing the IMessageFilter will have; it seems like it should work, but I don't know if there will be other implications to doing this (such as if, for whatever reason, the Handle needs to be recreated on the button and then this message filter no longer works).  Personally, I would go with a different approach if you have an OK and Cancel button, since these should be what determine whether the data gets updated or not.

-Matt