Mine

     private void textBox3_Validating(object sender, CancelEventArgs e)
        {
            try
            {
                short.Parse(textBox3.Text);
            }
            catch (Exception)
            {
                e.Cancel = true;
            }
        }

        internal void RemoveClipboardHandler()
        {
            WinApi.ChangeClipboardChain(Handle, _nextCBHandler);
        }