private void TelephoneTB_Validating(object sender, CancelEventArgs e)
{
string tel = TelephoneTB.Text.Trim();
if (string.IsNullOrEmpty(tel) || TelephoneTB.TextLength != 10)
{
TelephoneErr.SetError(TelephoneTB, "The telephone number must have 10 characters.");
e.Cancel = true;
}
}
private void TelephoneTB_Validated(object sender, EventArgs e)
{
TelephoneErr.Clear();
}