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

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The error message(s):

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

System.Windows.Forms.DataGridViewCell.Value.get returned null.

When I run this code data Save and Update in my Database Correctly
but Exception Thrown and when I open my database data save correctly.

Exception Thrown this Line

cmd.Parameters.AddWithValue("@BodyM", row.Cells["BodyM"].Value.ToString());

What I have tried:

C#

private void SaveUpdateBodyMeasurement()
        {
            foreach (DataGridViewRow row in dataGridView1.Rows)
            {
                SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["DataConnectionString"].ConnectionString);
                string SaveUpdateBM = "update BD set BodyM = @BodyM, Mess = @Mess where ID=@ID IF @@ROWCOUNT=0 insert into BD (OrderNo, BodyM, Mess) VALUES (@OrderNo, @BodyM, @Mess)";
                using (SqlCommand cmd = new SqlCommand(SaveUpdateBM, con))
                {
                    con.Open();
                    cmd.Parameters.AddWithValue("@ID", row.Cells["ID"].Value);
                    cmd.Parameters.AddWithValue("@OrderNo", Convert.ToInt32(txtOrder_No.Text));
                    cmd.Parameters.AddWithValue("@BodyM", row.Cells["BodyM"].Value.ToString());
                    cmd.Parameters.AddWithValue("@Mess", Convert.ToInt32(row.Cells["Mess"].Value));

                    cmd.ExecuteNonQuery();
                    con.Close();
                }
            }

        }

Posted 31-Mar-21 3:46am

Amar chand123

Updated 31-Mar-21 7:07am

Patrice T

v3

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OriginalGriff · Answer 1 · 2021-03-31T04:04:00

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, VS 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, VS will stop before the error, and let you examine what is going on by stepping through the code looking at your values.
Start by finding out which row is involved with the debugger, and move on from there.

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!

Tony Hill · Answer 2 · 2021-03-31T03:56:00

Your problem is probably because there is no value in that cell for that row and you are trying to convert the contents of that cell to a string with .ToString(), because the cell is null the ToString() throws an exception be cause it cannot convert null to a string.

You should test

row.Cells["BodyM"].Value

To see if it is null

thatraja · Answer 3 · 2021-03-31T06:56:00

First learn about that particular error message.
What Is NullReferenceException? Object reference not set to an instance of an object – Stackify[^]

And debug your code always to solve most of issues quickly.
Tutorial: Debug C# code - Visual Studio | Microsoft Docs[^]

Set a breakpoint on exception thrown line, run your code & see the value.

cmd.Parameters.AddWithValue("@BodyM", row.Cells["BodyM"].Value.ToString());

Use Quick Watch(Shift + F9) to see the value.
Here simple example to check your values while debugging. Ensure you're getting value for row.Cells["BodyM"].Value, if you're getting null, check value for row.Cells["BodyM"]. If you're getting null here, check value for row.Cells & just row

Based on above observations, you need to handle things.

Here a simple code to handle not null.

C#

string strBodyM = string.Empty;
if(row.Cells["BodyM"].Value != null)//If Value is NOT NULL
{
   strBodyM = row.Cells["BodyM"].Value.ToString();
}

cmd.Parameters.AddWithValue("@BodyM", strBodyM);

If you're getting null for row.Cells["BodyM"] itself, then you need to check things on other sides. Ensure name is BodyM. Sometime typos giving this error.

Now proceed further on making changes in your code.

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

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