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I have form 2 class to handle connected clients, and i have datagridview in that i added one button column and now i have to do is what , send data to connected client without clients request, the data which need to send to client is in another method other than dgv event.

    public class Form1()
      NetworkStream networkStream; 

      public void startClient(TcpClient inClientSocket, string clineNo) /// for handling clients///
        this.clientSocket = inClientSocket;
         inClientSocket.NoDelay = true;
        this.clNo = clineNo;
        new Thread(GetData).Start();

       public void GetData() // to run server //
           networkStream = clientSocket.GetStream();

         for (int p = 0; p >= 0; p++)
          b = new byte[5000];

          int k = networkStream.Read(b, 0, b.Length);

           for (int i = 0; i < k; i++)

 private void dataGridView1_CellContentClick(object sender, DataGridViewCellEventArgs e)
 if (senderGrid.Columns[e.ColumnIndex] is DataGridViewButtonColumn && e.RowIndex >=  0)
    foreach (DataGridViewRow row in dataGridView1.Rows)
       if (Convert.ToBoolean(row.Cells[SerialNo.Name].Value) == true)
          for (int i = 0; i <= row.Cells.Count - 1; i++)
             row.Cells[i].Style.BackColor = Color.LightSalmon;
     row.Cells[SerialNo.Name].Value = false;
    isButtonClicked = true;
     ans = MessageBox.Show("Are you sure to send indent?", "Save & Print",             MessageBoxButtons.YesNo, MessageBoxIcon.Question);

     if (ans == DialogResult.Yes)
      byte[] info = Encoding.ASCII.GetBytes(data);
      networkStream.Write(info, 0, info.Length);  ///error is in this line///
      hash = Encoding.ASCII.GetBytes("#");
      networkStream.Write(hash, 0, hash.Length);

in the above code i am declaring networkstream object globaly then assign values in "GetData" method and after asigning values it used in dgv event . but shows above error and object gets null value. 
Updated 8-Dec-15 21:03pm
In what line?
Member 11543226 9-Dec-15 3:04am
the bold line in dgv event see my edited answer. actually the "clienSocket" object of tcp client gets null value when if outside getdata.
There is no such event, "dgv", and your code doesn't show it. Isn't it simple: just comment the line where the exception it thrown, and refer to this comment in your explanation of the problem?

And I already gave you a detailed answer. Dig it out; it's way too easy.


1 solution

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Solution 1

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:,

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:

Good luck,

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