登陆出错，请给予解决

Question

 if (textBox_user.Text == "")
            {
               MessageBox.Show("用户名为空！");
               textBox_user.Focus();
                return;
            }
            if (textBox_pwd.Text == "")
            {
                MessageBox.Show("密码不能为空！");
                textBox_pwd.Focus();
                return;
            }
            SqlConnection cmd12 = new SqlConnection("server=127.0.0.1;uid=sa;pwd=123;database=REMIS");
            string str12 = "select uid,pwd from user where uid='" +textBox_user.Text+"'and pwd='" +textBox_pwd.Text+"'";
            cmd12.Open();
            SqlCommand com = new SqlCommand(str12,cmd12); ;
            SqlDataReader dr = com.ExecuteReader();
            if (dr.Read())
            {
                this.Close();
                new ALL().Show();
                
            }
            else
            {
                MessageBox.Show("登录错误，请重新输入！");
                textBox_user.Clear();
                textBox_pwd.Clear();
                cmd12.Close();
            }

Answer 1

string str12 = "select count(*) from user where uid='" +textBox_user.Text+"'and pwd='" +textBox_pwd.Text+"'";
            cmd12.Open();
            SqlCommand com = new SqlCommand(str12,cmd12); ;
            int sum=Convert.ToInt32(com.ExecuteScalar());
            if (sum>0)
            {
                //成功
                new ALL().Show();
               
            }
            else
            {
                MessageBox.Show("登录错误，请重新输入！");
                textBox_user.Clear();
                textBox_pwd.Clear();
                cmd12.Close();
            }
楼主对象实例命名有点问题，取的名字不好理解

Answer 2

            dr.Read()
            if (dr.HasRows)  这个改下试试 
            { 
                this.Close(); 
                new ALL().Show(); 
                
            } 
            else 
            { 
                MessageBox.Show("登录错误，请重新输入！"); 
                textBox_user.Clear(); 
                textBox_pwd.Clear(); 
                cmd12.Close(); 
            }

Answer 3

string str12 = "select count(*) from user where uid='" +textBox_user.Text+"'and pwd='" +textBox_pwd.Text+"'"; 
            cmd12.Open(); 
            SqlCommand com = new SqlCommand(str12,cmd12); ; 
            SqlDataReader dr = new SqlDataReader(com); 
            // 数据的取得
              DataSet ds = new DataSet();
            dr.Fill(ds);
            DateTable dtlResult = ds.Tables[0];
            if (dtSearch.Rows.Count > 0) 
            { 
                //成功 
                new ALL().Show(); 
              
            } 
            else 
            { 
                MessageBox.Show("登录错误，请重新输入！"); 
                textBox_user.Clear(); 
                textBox_pwd.Clear(); 
            } 
            cmd12.Close();