how to generate keypress even?

private void textBox4_KeyPress(object sender, KeyPressEventArgs e)
{
    int ascii = Convert.ToInt16(e.KeyChar);

    if ((ascii >= 97 && ascii <= 122) || (ascii >= 65 && ascii <= 90) || (ascii == 8))
    {

        e.Handled = false;

    }

    else
    {

        e.Handled = true;

    }
}