Question

I am just adding validation into a new winform. I am using the validating and validated events, in conjunction with an error provider control. Please see code below.

No problem with first validation (ie. if user enters more than 12 characters). Error is set in validating event, and error stays until user enters 12 or less characters. Validated event is then entered and error is reset to empty string.

However, there is a problem with the 2nd validation on same text box. The code checks for zero length in text box.. and sets error with provider. Watching in the debugger, this code is indeed invoked, and error is set ok. Then something weird happens, the validated event is (unexpectedly) fired, and the code there promptly resets the error.

Why is the validated event fired when there is already an error set ? This seems like a .NET bug. Can anyone suggest another way of doing this, or say what I am doing wrong ?

Thanks,

Bazza

Private Sub SampleCodeTextBox_Validating(sender As Object, e As System.ComponentModel.CancelEventArgs) Handles SampleCodeTextBox.Validating
    If SampleCodeTextBox.Text.Length > 12 Then
        e.Cancel = True
        FormErrorProvider.SetError(SampleCodeTextBox, "Max of 12 characters for sample code")
    End If

    If SampleCodeTextBox.Text.Trim.Length = 0 Then
        FormErrorProvider.SetError(SampleCodeTextBox, "Must enter a sample code")
    End If
End Sub

Private Sub SampleCodeTextBox_Validated(sender As Object, e As System.EventArgs) Handles SampleCodeTextBox.Validated
    FormErrorProvider.SetError(SampleCodeTextBox, "")
End Sub

Answer 1

You need to set the CancelEventArgs.Cancel property to True when your zero-length Text check fails in your Validating event handler.

From the MSDN article on the Control.Validated Event:

If the Cancel property of the CancelEventArgs is set to true in the
Validating event delegate, all events that would usually occur after
the Validating event are suppressed.