System.nullreferenceexception: 'object reference not set to an instance of an object.'

Question

1.00/5 (1 vote)

See more:

Hello everyone.
i faced NullReferenceException the code is working fine but when i search category name and edit the value is showing that error

What I have tried:

C#

private void guna2DataGridView1_CellClick(object sender, DataGridViewCellEventArgs e)
        {
            if (guna2DataGridView1.CurrentCell.OwningColumn.Name == "dgvedit")
            {
                frmCategoryAdd frm = new frmCategoryAdd();
                frm.id = Convert.ToInt32(guna2DataGridView1.CurrentRow.Cells["dgvid"].Value);
                frm.txtName.Text= Convert.ToString(guna2DataGridView1.CurrentRow.Cells["dgvName"].Value);
                MainClass.BlurBackground(frm);
                GetData();

            }
            if (guna2DataGridView1.CurrentCell.OwningColumn.Name == "dgvdel")
            {
                guna2MessageDialog1.Icon = Guna.UI2.WinForms.MessageDialogIcon.Question;
                guna2MessageDialog1.Buttons = Guna.UI2.WinForms.MessageDialogButtons.YesNo;
                if (guna2MessageDialog1.Show("Are you sure you want to delete?") == DialogResult.Yes)
                {
                    int id = Convert.ToInt32(guna2DataGridView1.CurrentRow.Cells["dgvid"].Value);
                    string qry = "delete from category where catID=" + id + "";
                    Hashtable ht = new Hashtable();
                    MainClass.SQL(qry, ht);
                    guna2MessageDialog1.Icon = Guna.UI2.WinForms.MessageDialogIcon.Information;
                    guna2MessageDialog1.Buttons = Guna.UI2.WinForms.MessageDialogButtons.OK;
                    guna2MessageDialog1.Show("Deleted Seccessfully");
                    GetData();
                }

            }
    }

Posted 19-Jan-23 11:16am

zmzk_1

Updated 19-Jan-23 20:14pm

PIEBALDconsult

v4

Add a Solution

Comments

Graeme_Grant 19-Jan-23 18:14pm

Which line of code does the error happen on? Please update your quest with the full error. This will have the answer for you.

Also, here is a good article on what the error is and how to handle it: Debugging System.NullReferenceException[^]

2 solutions

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)

Sandeep Mewara · Accepted Answer · 2023-01-19T17:08:00

Details about the error you see: NullReferenceException Class (System) | Microsoft Docs[^]

Quote:
A NullReferenceException exception is thrown when you try to access a member on a type whose value is null

Possibly because:
1. You've forgotten to instantiate a reference type
2. You've forgotten to dimension an array before initializing it.
3. You get a null return value from a method, and then call a method on the returned type.
4. You're using an expression (for example, you're chaining a list of methods or properties together) to retrieve a value
5. You're enumerating the elements of an array that contains reference types, and your attempt to process one of the elements throws
6. Exception is thrown by a method that is passed null

Following will help you learn about debugging:
Tutorial: Debug Visual Basic code - Visual Studio | Microsoft Docs[^]
First look at the debugger - Visual Studio | Microsoft Docs[^]

When you debug, you will be able to get the exact line where the variable is NULL and error is being raised. Handle the case and you will be able to resolve it.

To start with, in the code shared above, all the lines where you are doing Convert.ToString are potential possible culprits.

Try out!

OriginalGriff · Accepted Answer · 2023-01-19T20:14:00

This is one of the most common problems we get asked, and it's also the one we are least equipped to answer, but you are most equipped to answer yourself.

Let me just explain what the error means: You have tried to use a variable, property, or a method return value but it contains null - which means that there is no instance of a class in the variable.
It's a bit like a pocket: you have a pocket in your shirt, which you use to hold a pen. If you reach into the pocket and find there isn't a pen there, you can't sign your name on a piece of paper - and you will get very funny looks if you try! The empty pocket is giving you a null value (no pen here!) so you can't do anything that you would normally do once you retrieved your pen. Why is it empty? That's the question - it may be that you forgot to pick up your pen when you left the house this morning, or possibly you left the pen in the pocket of yesterday's shirt when you took it off last night.

We can't tell, because we weren't there, and even more importantly, we can't even see your shirt, much less what is in the pocket!

Back to computers, and you have done the same thing, somehow - and we can't see your code, much less run it and find out what contains null when it shouldn't.
But you can - and Visual Studio will help you here. Run your program in the debugger and when it fails, it will show you the line it found the problem on. You can then start looking at the various parts of it to see what value is null and start looking back through your code to find out why. So put a breakpoint at the beginning of the method containing the error line, and run your program from the start again. This time, the debugger will stop before the error, and let you examine what is going on by stepping through the code looking at your values.

But we can't do that - we don't have your code, we don't know how to use it if we did have it, we don't have your data. So try it - and see how much information you can find out!

System.nullreferenceexception: 'object reference not set to an instance of an object.'

2 solutions

Solution 1

Solution 2

Add your solution here

Preview 0