Object reference to get an instance an object error on delete button

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Hello, Guys, I hope you will be fine.I am facing another issue in my project and now that is when I delete values so I get an error I am using a checkbox for selected multiple rows by data grid view and delete all selected rows but when I click the button so sometimes it delete but mostly I will get an error.

What I have tried:

C#

foreach (DataGridViewRow item in this.dataGridView1.Rows)
            {
                if (bool.Parse(item.Cells[1].Value.ToString()))
                {
                    con_string.Open();
                    OleDbCommand command = new OleDbCommand();
                    command.Connection = con_string;
                    command.CommandText = "Delete from [Runtime] Where [Values] = " + item.Cells[0].Value.ToString() + "";
                    command.ExecuteNonQuery();
                    con_string.Close();
                }
            }

Posted 15-Jun-17 17:54pm

Member 9983063

Updated 15-Jun-17 18:10pm

Wendelius

v2

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Wendelius · Accepted Answer · 2017-06-15T18:09:00

Solution 1

One problem is that you concatenate the values directly to the SQL statement. This introduces conversion errors, leaves you open to SQL injections and so on.

The fix would be to use OleDbParameter objects. While the article is using SqlParamater, the idea is the same so have a look at Properly executing database operations[^]

Posted 15-Jun-17 18:09pm

Wendelius

Updated 15-Jun-17 18:10pm

v2

Comments

Member 9983063 16-Jun-17 0:14am

i have also tried oledbparams

Wendelius 16-Jun-17 0:25am

What was the error you got with them?

Member 9983063 16-Jun-17 6:18am

same error

Wendelius 16-Jun-17 8:04am

On which line?

Member 9983063 16-Jun-17 8:13am

in this line

if (bool.Parse(item.Cells[1].Value.ToString()))

Wendelius 16-Jun-17 8:39am

Now using debugger, check:
- Does the item contain the specified cell. In other words, is item.Cells[1] null? In this case Value will fail
- If it's not null then does it have a value or is Value null. In this case ToString will fail

Member 9983063 16-Jun-17 8:43am

hmmm i think tostring is fail bcz i have values in my db

Member 9983063 16-Jun-17 8:50am

how can i solve it if string has failed so

Wendelius 16-Jun-17 8:57am

As said, use the debugger to make sure this is the problem.

To resolve this, change code to something like

if (item.Cells[1].Value != null && bool.Parse(item.Cells[1].Value.ToString()))
{
...

But also note that as said in the beginning, you really should use paremeters

Member 9983063 16-Jun-17 9:08am

Thanks man it's working you make my day thank you so much

Wendelius 16-Jun-17 17:57pm

Glad if it helped!