C#Winform如何获取登录时输入的用户名

我在登录页面获取了：UserHelper.loginId = txtLoginId.Text;
                    UserHelper.loginPwd = txtLoginPwd.Text;

但是加断点调试时看到的值是空值，这是怎么回事？
这是应该显示用户信息的页面！
            txtLogId.Text = UserHelper.loginId;
            txtpwd.Text = UserHelper.loginPwd;

            string constr = "Server=.;DataBase=MySchool;Uid=sa;Pwd=yule9616866@;Integrated Security=true";
            SqlConnection con = new SqlConnection(constr);
            con.Open();
            SqlCommand cmd = new SqlCommand();
            cmd.Connection = con;
             = CommandType.Text;
             = "select LoginPwd,UserStateId,TeacherName,Sex,Birthday from Teacher where LoginId = '" + txtLogId.Text  + "'and LoginPwd='"+txtpwd .Text+"'";
            SqlDataReader dr = cmd.ExecuteReader();

            dr.Read();
            txtLogId.Text = dr["LoginId"].ToString();
            txtpwd.Text = dr["LoginPwd"].ToString();
            txtSpwd.Text = "";
            cmbLogState.Text = dr["UserStateId"].ToString();
            txtLogName.Text = dr["TeacherName"].ToString();
            txtLogSex.Text = dr["Sex"].ToString();
            dateTimePicker1.Text = dr["Birthday"].ToString();