textbox只能输入小数

/// <summary>
/// txtbox只能输入小数
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
        private void txtzhongxiang_KeyPress(object sender, KeyPressEventArgs e)
        {
            if (!(Char.IsNumber(e.KeyChar)) && e.KeyChar != (char)13 && e.KeyChar != (char)8)
            {
                int i = ((TextBox)sender).Text.IndexOf('.');
                if (e.KeyChar == '.' && ((TextBox)sender).Text.IndexOf('.') == -1)
                {

                    e.Handled = false;
                }
                else
                {
                    e.Handled = true;
                }
            }
            else
            {
                if (e.KeyChar == (char)13)
                {
                    button3_Click(sender, e);
                }
                else
                    e.Handled = false;
            }
        }