textbox只能输入数字

        private void txt_tel_KeyPress(object sender, KeyPressEventArgs e)
        {
            //允许输入的字符
            string AstrictChar = "0123456789-";

            //「BackSpace」「Delete」后退键正常删除操作
            if ((Keys)(e.KeyChar) == Keys.Back || (Keys)(e.KeyChar) == Keys.Delete)
            {
                return;
            }
            //「Ctrl+C」(3)「Ctrl+X」(24)特殊组合键正常
            //「Ctrl+Z」(26) 撤消组合键正常
            if ((e.KeyChar == 3) || (e.KeyChar == 24) || (e.KeyChar == 26))
            {
                return;
            }

            //允许输入的字符外，
            if (AstrictChar.IndexOf(e.KeyChar.ToString()) == -1)
            {
                e.Handled = true;
                return;
            }

        }