[2005] DateTimePicker Valuechanged event firing twice??

[Ginolard]

This seems pretty straighforward. I have two DateTimePickers. One for a start date and the other for an end date.

I want to check when each one has changed to ensure that the dates are consistent (ie. end date is greater than start date).

This is the code I have so far.

      Private Sub dtp_SchTaskEnd_ValueChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles dtp_SchTaskEnd.ValueChanged
        Dim dtp As DateTimePicker = DirectCast(sender, DateTimePicker)
        If dtp.Value.ToShortDateString < Me.dtp_SchTaskStart.Value.ToShortDateString Then
            MessageBox.Show("End date cannot be earlier than start date", "Wrong end date", MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
            dtp.Value = Me.dtp_SchTaskStart.Value
        End If
    End Sub

However, the warning message gets shown twice if the If condition is true. Why is that?

[Atheist]

It would probably be because you are setting the value of the datetimepicker inside the eventhandler:

dtp.Value = Me.dtp_SchTaskStart.Value

I would do this instead:

Private Sub DateTimePicker1_ValueChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles DateTimePicker1.ValueChanged
        DateTimePicker2.MinDate = DateTimePicker1.Value
    End Sub
 
    Private Sub DateTimePicker2_ValueChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles DateTimePicker2.ValueChanged
        DateTimePicker1.MaxDate = DateTimePicker2.Value
    End Sub

DateTimePicker1 can never have a date higher than the date in DateTimePicker2, and DateTimePicker2 can never have a date lower than the date in DateTimePicker1.
No need for error messages