How to solve this "object reference not set to an instance of an object"

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C#

For r As Integer = 0 To DataGridView1.Columns.Count - 1

         For i As Integer = 0 To DataGridView1.Rows.Count - 1

             con.Open()
             accountno = DataGridView1.Rows(i).Cells(0).Value.ToString
             accountno = DataGridView1.Columns(r).ToString

             area = DataGridView1.Rows(i).Cells(1).Value.ToString
             area = DataGridView1.Columns(r).ToString

             accountname = DataGridView1.Rows(i).Cells(2).Value.ToString
             accountname = DataGridView1.Columns(r).ToString

             address = DataGridView1.Rows(i).Cells(3).Value.ToString
             address = DataGridView1.Columns(r).ToString

             yr = DataGridView1.Rows(i).Cells(4).Value.ToString
             yr = DataGridView1.Columns(r).ToString

             fname = DataGridView1.Rows(i).Cells(5).Value.ToString
             fname = DataGridView1.Columns(r).ToString

             mname = DataGridView1.Rows(i).Cells(6).Value.ToString
             mname = DataGridView1.Columns(r).ToString

             lname = DataGridView1.Rows(i).Cells(7).Value.ToString
             lname = DataGridView1.Columns(r).ToString

             sqlComm.Connection = con

What I have tried:

how to solve this "Object reference not set to an instance of an object"

Posted 4-Feb-16 12:25pm

ElLo25

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[no name] 4-Feb-16 18:44pm

Please tell us: At which Statement this "Object reference not set to an instance of an object" occures?

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Sergey Alexandrovich Kryukov · Answer 1 · 2016-02-04T12:46:00

You did not show where the exception with the message "Object reference not set to an instance of an object" is thrown.

Not to worry. This is one of the very easiest cases to detect and fix. It simply means that some member/variable of some reference type is dereferences by using and of its instance (non-static) members, which requires this member/variable to be non-null, but in fact it appears to be null. Simply execute it under debugger, it will stop the execution where the exception is thrown. Put a break point on that line, restart the application and come to this point again. Evaluate all references involved in next line and see which one is null while it needs to be not null. After you figure this out, fix the code: either make sure the member/variable is properly initialized to a non-null reference, or check it for null and, in case of null, do something else.

Please see also: want to display next record on button click. but got an error in if condition of next record function "object reference not set to an instance of an object".

Sometimes, you cannot do it under debugger, by one or another reason. One really nasty case is when the problem is only manifested if software is built when debug information is not available. In this case, you have to use the harder way. First, you need to make sure that you never block propagation of exceptions by handling them silently (this is a crime of developers against themselves, yet very usual). The you need to catch absolutely all exceptions on the very top stack frame of each thread. You can do it if you handle the exceptions of the type System.Exception. In the handler, you need to log all the exception information, especially the System.Exception.StackTrace:
http://msdn.microsoft.com/en-us/library/system.exception.aspx,
http://msdn.microsoft.com/en-us/library/system.exception.stacktrace.aspx.

The stack trace is just a string showing the full path of exception propagation from the throw statement to the handler. By reading it, you can always find ends. For logging, it's the best (in most cases) to use the class System.Diagnostics.EventLog:
http://msdn.microsoft.com/en-us/library/system.diagnostics.eventlog.aspx.

Good luck,

—SA

Sascha Lefèvre · Answer 2 · 2016-02-04T12:51:00

You don't tell on which line this exception occurs and it's not obvious, so I can't pinpoint it.

In general, it means that you didn't initialize a variable that is supposed to reference an object, e.g.:

VB

Dim s As String
Console.WriteLine(s.Length) ' <---

On the marked line you would get the same exception. Because s, though declared, is not initialized. It's like a door handle not attached to a door :)

Likely candidates from the shown code are con and sqlComm.

Run your code in the debugger and look at the code line that gets pinpointed by the exception. Then hover your mouse over the variable(s) on that line to find which one shows up as Nothing in the tooltip. Then do something about that.

How to solve this "object reference not set to an instance of an object"

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