提交新用户时注册表单出错。 [英] Error on registration form when submitting a new user.

问题描述

我有一个注册新用户的表单。当用户输入他们的电子邮件地址和密码然后单击提交我收到错误：System.NullReferenceException {对象引用未设置为对象的实例。}。这是什么错误，我该如何解决？错误发生在第29行。该行是：

  int  temp = Convert.ToInt32（userExist。 ExecuteScalar（）。ToString（））; 

以下是表单的所有代码：

 使用系统; 
 使用 System.Collections.Generic; 
 使用 System.Linq; 
 使用 System.Web; 
 使用 System.Web.UI; 
 使用 System.Web.UI.WebControls; 
 使用 System.Data.SqlClient; 
 使用 System.Configuration; 
 使用 System.Web.Security; 
 使用 System.Security.Cryptography; 
 
  public   partial   class  SubmitPage：System.Web.UI.Page 
 {
  protected   void  Page_Load（ object  sender，EventArgs e）
 {
  if （IsPostBack） 
 {
 SqlConnection con =  new  SqlConnection（System.Configuration.ConfigurationManager.ConnectionStrings [  PasswordConnectionString]。ConnectionString）; 
 con.Open（）; 
 
  string  cmdStr =  从TableSecurity中选择INST_ID，EmailAddress，其中EmailAddress =' + TextBoxEA.Text +  '; 
  string  cmdStr2 =  选择INST_ID，EmailAddress来自TableCEO，其中EmailAddress =' + TextBoxEA.Text +  '; 
  string  cmdStr3 =  选择INST_ID，EmailAddress来自TableialO，其中EmailAddress =' + TextBoxEA.Text +  '; 
 
 SqlCommand userExist =  new  SqlCommand（cmdStr，con）; 
 SqlCommand cmd =  new  SqlCommand（  select INST_ID，来自TableSecurity的电子邮件地址，con）; 
 SqlCommand cmd2 =  new  SqlCommand（  select来自TableCEO的INST_ID，EmailAddress，con）; 
 SqlCommand cmd3 =  new  SqlCommand（  select来自TableIALO的INST_ID，EmailAddress，con）; 
  int  temp = Convert.ToInt32（userExist.ExecuteScalar（）。ToString（））; 
  if （temp ==  1 ）
 
 Response.Write （ 用户名已存在!!!< br />请选择其他用户名。 ）; 
} 
 
 
 
} 
 
 受保护  void  Submit_Click（ object  sender，EventArgs e）
 {
 SqlConnection con =  new  SqlConnection（System.Configuration.ConfigurationManager.ConnectionStrings [  PasswordConnectionString ] .ConnectionString）; 
 con.Open（）; 
 
  string  chkUser =  从TableCEO中选择INST_ID，EmailAddress，其中EmailAddress' + TextBoxEA.Text +  ; 
 chkUser =  从TableialO中选择INST_ID，EmailAddress，其中EmailAddress' + TextBoxPW.Text +  ; 
 SqlCommand chkUsercmd =  new  SqlCommand（chkUser，con）; 
 
 
  string  insCmd =  插入TableSecurity（INST_ID，EmailAddress，Password）值（@INST_ID，@ EmailAddress，@ Password）; 
 SqlCommand insertUser =  new  SqlCommand（insCmd，con）; 
 insertUser.Parameters.AddWithValue（  @ EmailAddress，TextBoxEA.Text）; 
 insertUser.Parameters.AddWithValue（  @ Password，TextBoxPW.Text）; 
 
 
 
  try  
 {
 insertUser.ExecuteNonQuery（）; 
 con.Close（）; 
 Response.Redirect（  Login.aspx）; 
} 
  catch （例外）
 {
 Response.Write（ 发生错误： + er.Message）; 
} 
 最后 
 {
} 
} 
 
} 

解决方案

你是个好程序员......



但是......是我注意到的一件事....你在将参数传递给SqlCommand对象时错过了一行添加到你的代码中。



< br $> b $ b

  //  您的代码....  
 
 字符串 insCmd =  < span class =code-string>插入TableSecurity（INST_ID，EmailAddress，Password）值（@INST_ID，@ EmailAddress，@ Password）; 
 SqlCommand insertUser =  new  SqlCommand（insCmd，con）; 
 
 
 
  //  以下是解决方案 -   
  //  将@INST_ID添加到SQLCommand  
 
 insertUser .Parameters.AddWithValue（  @ INST_ID，'  TextBoxName.Text'）; 
 
  //   ---------------- ----  
 
  //  您的代码......  
 insertUser.Parameters.AddWithValue（  @ EmailAddress，TextBoxEA.Text）; 
 insertUser.Parameters.AddWithValue（  @ Password，TextBoxPW.Text）; 

Yup ....



从所需的表中获取INST_ID的值...而且只是将它分配给局部变量...然后将其值而不是Textbox传递给SqlCommand对象

  int  tempID = ' 用于检索唯一INST_ID的代码' 
 
 insertUser.Parameters.AddWithValue（  @ INST_ID， tempID）; 

I have a form that registraters a new user. When the user puts in their email address and password then click submit I get an error for: System.NullReferenceException {"Object reference not set to an instance of an object."}. What is this error and how can I fix it? The error happens on line 29. that line is:

int temp = Convert.ToInt32(userExist.ExecuteScalar().ToString());

Here is all of the code for the form:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Configuration;
using System.Web.Security;
using System.Security.Cryptography;

public partial class SubmitPage : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (IsPostBack)
        {
            SqlConnection con = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["PasswordConnectionString"].ConnectionString);
            con.Open();

            string cmdStr = "Select INST_ID, EmailAddress from TableSecurity where EmailAddress='" + TextBoxEA.Text + "'";
            string cmdStr2 = "Select INST_ID, EmailAddress from TableCEO where EmailAddress ='" + TextBoxEA.Text + "'";
            string cmdStr3 = "Select INST_ID, EmailAddress from TableIALO where EmailAddress ='" + TextBoxEA.Text + "'";
            
            SqlCommand userExist = new SqlCommand(cmdStr, con);
            SqlCommand cmd = new SqlCommand("select INST_ID, EmailAddress from TableSecurity", con);
            SqlCommand cmd2 = new SqlCommand("select INST_ID, EmailAddress from TableCEO", con);
            SqlCommand cmd3 = new SqlCommand("select INST_ID, EmailAddress from TableIALO", con);
            int temp = Convert.ToInt32(userExist.ExecuteScalar().ToString());
            if (temp == 1)

                Response.Write("User Name Already Exist!!!<br /> Please Choose Another User Name.");
        }



    }

    protected void Submit_Click(object sender, EventArgs e)
    {
        SqlConnection con = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["PasswordConnectionString"].ConnectionString);
        con.Open();

        string chkUser = "select INST_ID, EmailAddress from TableCEO where EmailAddress'" + TextBoxEA.Text + "";
        chkUser = "select INST_ID, EmailAddress from TableIALO where EmailAddress'" + TextBoxPW.Text + "";
        SqlCommand chkUsercmd = new SqlCommand(chkUser, con);


        string insCmd = "Insert into TableSecurity (INST_ID, EmailAddress, Password) values (@INST_ID, @EmailAddress, @Password)";
        SqlCommand insertUser = new SqlCommand(insCmd, con);
        insertUser.Parameters.AddWithValue("@EmailAddress", TextBoxEA.Text);
        insertUser.Parameters.AddWithValue("@Password", TextBoxPW.Text);
        


        try
        {
            insertUser.ExecuteNonQuery();
            con.Close();
            Response.Redirect("Login.aspx");
        }
        catch (Exception er)
        {
            Response.Write("An error occurred: " + er.Message);
        }
        finally
        {
        }
    }
    
}

解决方案

You are Good Programmer....

But..there is One thing I noticed.... that....you just missed a single line to add into your code while passing Parameters to the SqlCommand Object.

//Your Code....

string insCmd = "Insert into TableSecurity (INST_ID, EmailAddress, Password) values (@INST_ID, @EmailAddress, @Password)";
SqlCommand insertUser = new SqlCommand(insCmd, con);



//Here is the Solution--
//Add @INST_ID to SQLCommand

        insertUser.Parameters.AddWithValue("@INST_ID", 'TextBoxName.Text');

//--------------------

      //Your Code...
        insertUser.Parameters.AddWithValue("@EmailAddress", TextBoxEA.Text);
        insertUser.Parameters.AddWithValue("@Password", TextBoxPW.Text);

Yup....

Fetch the value of INST_ID from required table...and just assign it to the local variable ...then pass its value instead of Textbox into SqlCommand object

int tempID='code for retrieving unique INST_ID'

insertUser.Parameters.AddWithValue("@INST_ID", tempID);

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