private void txtArea_TextChanged_1(object sender, EventArgs e)
        {
            if (e.KeyChar != 8 && !char.IsDigit(e.KeyChar))
            {
                MessageBox.Show("只能输入数字", "提示",//弹出消息对话框
                    MessageBoxButtons.OK, MessageBoxIcon.Information);
                e.Handled = true;//已经处理过此事件
            }
        }