Object reference not set to an instance of an object.

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C#

GridViewRow gr = GridView1.Rows[e.RowIndex] as GridViewRow;
        TextBox t6 = gr.FindControl("txtEmpid") as TextBox;
        TextBox t3 = gr.FindControl("txtName") as TextBox;
        TextBox t5 = gr.FindControl("txtEmailid") as TextBox;

        SqlConnection conn = new SqlConnection(@"Data Source=ARVIND-VAIO\ARVIND;Initial Catalog=ARVIND;Integrated Security=True");
        SqlCommand cmd = new SqlCommand("update Emp_info set Name='"+t3.Text+"',Emailid='"+t5.Text+"' where Empid='"+t6.Text+"'", conn);
        conn.Open();
        cmd.ExecuteNonQuery();
        conn.Close();
        display();

I am getting error Object reference not set to an instance of an object.
The error is on the line with the SqlCommand call.

Posted 11-May-13 5:20am

Arvind Jha

Updated 11-May-13 5:22am

André Kraak

v3

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André Kraak 11-May-13 11:23am

Debug you program and check if the t3, t5 and t6 variables have a valid value.

Bikash Prakash Dash 11-May-13 11:29am

paste all the code of the event function.

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CPallini · Answer 1 · 2013-05-11T05:31:00

Solution 2

As alaready suggested, you use the debugger for checking that all the references ( t3, t5, t6 and conn) in the statement are set to valid objects (for instance did you use new on conn?).

Posted 11-May-13 5:31am

CPallini

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Arvind Jha 11-May-13 20:35pm

Ho to check with debugger they are set to valid objects or not?

OriginalGriff · Answer 2 · 2013-05-11T05:27:00

Two problems here:
1) Either one of your names is wrong: "txtEmpid", "txtName", or "txtEmailid" is incorrect, or one of them is not a textbox. This means that the "tn" variable gets a null, so you get the error when you try to use it's Text property. Check the names and types.

2) Do not concatenate strings to build a SQL command. It leaves you wide open to accidental or deliberate SQL Injection attack which can destroy your entire database. Use Parametrized queries instead. This is particularly a problem with website code, where your database can be deleted from the other side of the world...

"How to use parameterized queries and why?"

Why? To prevent me visiting your site from half a world away, and deleting your entire database by typing in your textboxes. Which seems like it might be a bad thing from your point of view.

Google for "Sql Injection" and "Bobby tables" and you will find good information on why you should never, ever concatenate SQL commands.

How? Parametrised queries are pretty easy: you provide a parameter name in your query, then add a parameter value to that:

C#

using (SqlConnection con = new SqlConnection(strConnect))
    {
    con.Open();
    using (SqlCommand com = new SqlCommand("UPDATE myTable SET myColumn1=@C1, myColumn2=@C2 WHERE Id=@ID", con))
        {
        com.Parameters.AddWithValue("@ID", id);
        com.Parameters.AddWithValue("@C1", myValueForColumn1);
        com.Parameters.AddWithValue("@C2", myValueForColumn2);
        com.ExecuteNonQuery();
        }
    }

In this example, @ID, @C1 and @C2 are the parameter names (which should always start with '@').