[RESOLVED] NoNullAllowedException error handling

[Mark@SF]

I have a scenario that is raising the System.Data.NoNullAllowedExceptionexception and I don't understand how to intercept (trap) it.

My form has 2 text boxes and both are bound to columns that don't allow null values (SQLite database fields are configured as "NOT NULL"). I have added the Validating events for these text boxes.

The following sequence of events raise the NoNullAllowedException exception:

1. The user opens the form (the first record is shown).
2. The user clicks the BindingNavigator.AddNewItem button (a new record is shown - the 2 text boxes are empty).
3. Without entering values in these 2 text boxes, the user clicks the BindingNavigator.MovePreviousItem button.

I have a global error handler that displays the stack trace.

'...inspect the StackTrace
If flgDebug Then
    Debug.WriteLine("{0}, {1}", mb.DeclaringType.Name, mb.Name)
    For i = 0 To st.GetFrames.Count - 1
        Debug.WriteLine("{0}. {1}", i, st.GetFrame(i).GetMethod.Name)
    Next i
End If

When the error handler is called, the immediate window shows the following sequence of 33 method calls:

DataColumn, CheckNullable
0. CheckNullable
1. RaiseRowChanging
2. SetNewRecordWorker
3. InsertRow
4. FinishAddNew
5. EndEdit
6. EndCurrentEdit
7. ChangeRecordState
8. set_Position
9. MoveFirst
10. OnMoveFirst
11. RaiseEvent
12. OnClick
13. HandleClick
14. HandleMouseUp
15. FireEventInteractive
16. FireEvent
17. OnMouseUp
18. WmMouseUp
19. WndProc
20. WndProc
21. WndProc
22. OnMessage
23. WndProc
24. DebuggableCallback
25. DispatchMessageW
26. System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop
27. RunMessageLoopInner
28. RunMessageLoop
29. RunDialog
30. ShowDialog
31. ShowDialog
32. tsmiDataWorkingQuestions_Click

With the exception of method #32 in the stack trace listing above, I don't know how to trap the above stack trace methods so I'm looking for help.

How can I trap the NoNullAllowedException exception in this scenario? I would like to avoid showing the error and instead call the BindingSource.RemoveCurrent method to abandon the newly added (blank) record.

[jmcilhinney]

I don't often use a BindingNavigator but I'm fairly sure that you can handle the Click events of the Buttons and cancel the navigation, so you could validate the current record and only allow navigation away from it if it passes.

[Mark@SF]

Thanks, jmc.

For anyone interested, here's my solution...

'...the Validate() method of the form verifies the value of the control losing focus by causing the Validating and Validated events to occur, in that order. (Inherited from ContainerControl.)
'...the Validate() method of a ContainerControl class validates the last child control that is not validated and its ancestors up through, but not including, the current container control.
If Validate() Then
    '...ignore, the Validating() methods for all controls have completed successfully
Else
    '...in this case, the Validating() method for a control on the form has failed (e.Cancel = True)
    '   and that method will notify the user, for example see the following:
    '    txtAccount.Validating()
    If DirectCast(bsMain.Current, DataRowView).IsNew Then
        '...the user has added a new record but hasn't entered a required value for one or more controls that are bound to fields that cannot be Null
        '   and the DataTable.EndEdit has been implicitly called by one of the BindingNavigator's navigation buttons
        '...the EndEdit method implicitly validates all controls on the form that have a Validating method (see above)
        '   and the associated control that does not have a required value has failed its validation
        MessageBox.Show("The new record's data has not been validated and therefore it will be abandoned.", strMethodName, MessageBoxButtons.OK, MessageBoxIcon.Information)
        bsMain.RemoveCurrent()
    Else
        '...this is not expected
        MessageBox.Show("Unexpected scenario, please contact the application developer.", strMethodName, MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
    End If
End If