C#登陆界面与数据库中的用户名和密码进行检查

        private void btnlogin_Click(object sender, EventArgs e)
        {
            if (txtname == null)
            {
                MessageBox.Show("请输入用户名","登录界面");
            }
            else if (txtpw == null)
            {
                MessageBox.Show("请输入密码", "登录界面");
            }
                string sql =string.Format( "select count(*) from usera where userid='{0}' and userpw='{1}'",txtname.Text.Trim(),txtpw.Text.Trim());
                SqlCommand cmd = new SqlCommand(sql, DbCon.Conn);
                DbCon.Conn.Open();
                int count = (int)cmd.ExecuteScalar();
                DbCon.Conn.Close();
                if (count == 1)
                {
                    Main Mf = new Main();
                    Mf.Show();
                    this.Hide();//隐藏此窗口
                }
                else
                {
                    MessageBox.Show("账号或密码错误！请确认后重新输入", "登录界面");
                }
        }