验证合法输入，数字和小数点

        private void textBoxLength_KeyPress(object sender, KeyPressEventArgs e)
        {
            if ((char.IsDigit(e.KeyChar)) || (e.KeyChar == 46) || (e.KeyChar == 8))//验证合法输入 （.0123456789）
                e.Handled = false;
            else
                e.Handled = true;
        }