C# 在修改登陆信息的问题

Question

if (this.tabControl1.SelectedTab.Text == this.tabPage2.Text)
            {
                string user2 = this.textBox4.Text.ToString().Trim();
                string psw21 = this.textBox5.Text.ToString().Trim();
                string psw22 = this.textBox6.Text.ToString().Trim();
                string psw23 = this.textBox7.Text.ToString().Trim();
                if (psw22 == psw23)//PSW22和PSW23是输入的新密码 和 确认密码
                {
                    try
                    {
                        con.Open();
                        string sql = "select * from admin";    //连接SQL数据库
                        SqlCommand com = new SqlCommand(sql, con);
                        SqlDataReader sdr = com.ExecuteReader();
                        sdr.Read();
                        if (Convert.ToString(sdr["password"]) == psw21 && Convert.ToString(sdr["user"]) == user2) //核对用户名和原来的老密码
                        {
                            string sql1 = "update admin set user='" + user2 + "',password='" + psw22 + "'";
                            SqlCommand com1 = new SqlCommand(sql1, con);
                            
                          com.ExecuteNonQuery();//错误提示“已有打开的与此命令相关联的 DataReader，必须首先将它关闭。”大家帮我看看应该怎么修改
                            con.Close();
                            MessageBox.Show("用户密码修改成功！", "完成");
                            this.textBox4.Text = "";
                            this.textBox5.Text = "";
                            this.textBox6.Text = "";
                            this.textBox7.Text = "";
                        }
                        else if (Convert.ToString(sdr["user"]) != user2)
                        {
                            MessageBox.Show("用户不存在，请重新输入！", "失败");
                            this.textBox4.Text = "";
                            this.textBox5.Text = "";
                            this.textBox6.Text = "";
                            this.textBox7.Text = "";
                        }else if(Convert.ToString(sdr["password"]) != psw21)
                        {
                            MessageBox.Show("旧密码错误，请重新输入！", "错误");
                            this.textBox5.Text = "";
                        }                    }
                    catch (SqlException e1)
                    {
                        MessageBox.Show("用户不存在，请重新输入！", "失败");
                        this.textBox4.Text = "";
                        this.textBox5.Text = "";
                        this.textBox6.Text = "";
                        this.textBox7.Text = "";
                    }
                    finally
                    {
                        con.Close();
                    }
                }
                else
                {
                    MessageBox.Show("两次输入密码不相同，请重新输入！", "错误");
                    this.textBox6.Text = "";
                    this.textBox7.Text = "";
                }
                
            }这是修改登陆密码的点击确定的源代码 

Answer 1

 com.ExecuteNonQuery();//[color=#FF0000]错误提示“已有打开的与此命令相关com1吧

Answer 2

 if (this.tabControl1.SelectedTab.Text == this.tabPage2.Text)
        {
            string user2 = this.textBox4.Text.ToString().Trim();
            string psw21 = this.textBox5.Text.ToString().Trim();
            string psw22 = this.textBox6.Text.ToString().Trim();
            string psw23 = this.textBox7.Text.ToString().Trim();
            if (psw22 == psw23)//PSW22和PSW23是输入的新密码 和 确认密码
            {
                try
                {
                    con.Open();
                    string sql = "select * from admin";    //连接SQL数据库
                    SqlCommand com = new SqlCommand(sql, con);
                    SqlDataReader sdr = com.ExecuteReader();
                    sdr.Read();
                    if (Convert.ToString(sdr["password"]) == psw21 && Convert.ToString(sdr["user"]) == user2) //核对用户名和原来的老密码
                    {
                        sdr.close();
                        string sql1 = "update admin set user='" + user2 + "',password='" + psw22 + "'";
                        SqlCommand com1 = new SqlCommand(sql1, con);                        com.ExecuteNonQuery();//错误提示“已有打开的与此命令相关联的 DataReader，必须首先将它关闭。”大家帮我看看应该怎么修改
                        con.Close();
                        MessageBox.Show("用户密码修改成功！", "完成");
                        this.textBox4.Text = "";
                        this.textBox5.Text = "";
                        this.textBox6.Text = "";
                        this.textBox7.Text = "";
                    }
                    else if (Convert.ToString(sdr["user"]) != user2)
                    {
                        MessageBox.Show("用户不存在，请重新输入！", "失败");
                        this.textBox4.Text = "";
                        this.textBox5.Text = "";
                        this.textBox6.Text = "";
                        this.textBox7.Text = "";
                    }
                    else if (Convert.ToString(sdr["password"]) != psw21)
                    {
                        MessageBox.Show("旧密码错误，请重新输入！", "错误");
                        this.textBox5.Text = "";
                    }                }
                catch (SqlException e1)
                {
                    MessageBox.Show("用户不存在，请重新输入！", "失败");
                    this.textBox4.Text = "";
                    this.textBox5.Text = "";
                    this.textBox6.Text = "";
                    this.textBox7.Text = "";
                }
                finally
                {
                    con.Close();
                }
            }
            else
            {
                MessageBox.Show("两次输入密码不相同，请重新输入！", "错误");
                this.textBox6.Text = "";
                this.textBox7.Text = "";
            }        }

Answer 3

你要执行前先关掉sdr 即可解决

Answer 4

有个疑问：表admin 中只有一条记录吗？
  如果只有一条记录还用数据库干什么？
  如果不是，要修改的账户正好在第一条记录吗？
  
建议第一条SQL语句修改为：select * from admin where user=@user,只获取第一条记录。sdr.Read(); //该为if(sdr.Read()){}或者两条合为一条：
   update admin set password=@newPassword where user=@user and password=@oldPassword执行方式改为：
int result=com.ExecuteNonQuery();
if(1==result)
{
    //用户密码修改成功
}
else
{
   //用户名或密码错误，信息更隐蔽
}