Object reference not set to an instance of an object

Question

1.00/5 (2 votes)

See more:

Please,Help

when insert data error show "

object reference not set to an instance of an object

".What can i dow for solve the problem.my code is

try
       {

           SqlDataAdapter sda = new SqlDataAdapter("SELECT * FROM tblItemEntry WHERE Item_Name='" + comboBox1.SelectedItem.ToString() + "'", con);
           DataTable dt = new DataTable();
           sda.Fill(dt);
           foreach (DataRow item in dt.Rows)
           {
               textBox1.Text = item["Item_ID"].ToString();
           }
       }
       catch(Exception ex)
       {
           MessageBox.Show(ex.Message);
       }

What I have tried:

try
            {

                SqlDataAdapter sda = new SqlDataAdapter("SELECT * FROM tblItemEntry WHERE Item_Name='" + comboBox1.SelectedItem.ToString() + "'", con);
                DataTable dt = new DataTable();
                sda.Fill(dt);
                foreach (DataRow item in dt.Rows)
                {
                    textBox1.Text = item["Item_ID"].ToString();
                }
            }
            catch(Exception ex)
            {
                MessageBox.Show(ex.Message);
            }

Posted 19-Jan-17 20:12pm

Methoun Ahmed

Updated 20-Jan-17 12:14pm

Add a Solution

Comments

F-ES Sitecore 20-Jan-17 4:19am

This is only one of the reasons you shouldn't use "select *". Your code is also open to SQL injection attacks so look into parameterised queries. Also when you get an error always say what line it occurs on so people aren't wasting their time guessing what your problem is.

Richard Deeming 20-Jan-17 9:21am

Everything you wanted to know about SQL injection (but were afraid to ask) | Troy Hunt[^]
How can I explain SQL injection without technical jargon? | Information Security Stack Exchange[^]
Query Parameterization Cheat Sheet | OWASP[^]

4 solutions

Solution 1

You should report all the details of the error message (e.g. what is the offending line?).

Quote:
extBox1.Text = item["Item_ID"].ToString();

if the "Item_ID" field doesn't exitst (for instance, if it is mistyped) then such an exception may arise.

Note, you should prefer parametric queries to the string concatenation approach.

Posted 19-Jan-17 21:15pm

CPallini

Solution 2

1. If the error in
(SqlDataAdapter sda = new SqlDataAdapter("SELECT * FROM tblItemEntry WHERE Item_Name='" + comboBox1.SelectedItem.ToString() + "'", con);) line then conncetion properties is not intilise properly.

2. If the error occoured in side foreach loop.

textBox1.Text = item["Item_ID"].ToString();

then it may be the ITEM_ID column name is not there the data row or ITEM_ID value may be null.

When the value is null and we try to convert it to string by help of function .ToString() then the Object reference issue.. occur.

Note: User Convert.Tostring(item["Item_ID"]) instead of tem["Item_ID"].ToString(); because Convert.Tostring() can handle null value.

Posted 19-Jan-17 22:39pm

Ramesh Kumar Barik

Solution 4

First remove the try/catch structure, and the error message will tell you where it crash, use debugger and set a breakpoint on offending line and inspect variables.

When you don't understand what your code is doing or why it does what it does, the answer is debugger.
Use the debugger to see what your code is doing. It allow you to execute lines 1 by 1 and to inspect variables as it execute, it is an incredible learning tool.

Debugger - Wikipedia, the free encyclopedia[^]
Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[^]

The debugger is here to show you what your code is doing and your task is to compare with what it should do.
There is no magic in the debugger, it don't find bugs, it just help you to. When the code don't do what is expected, you are close to a bug.

Posted 20-Jan-17 12:14pm

Patrice T

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

avinashkumar0509 · Accepted Answer · 2017-01-20T02:09:00

Solution 3

may be

comboBox1.SelectedItem.ToString()

would be null.
please set a debug point and debug and see where the value is null.

Posted 20-Jan-17 2:09am

avinashkumar0509

Comments

Methoun Ahmed 21-Jan-17 1:23am

I am already use comboBox1.SelectedItem.ToString()