C# tcplistener - send with a button

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C#

.NET

TCP/IP

Could someone shed some light on this problem for me, please?
I have a SocketListener and a Client winforms apps, they're based on the examples from MS: client, listener.

This Send method is done programmatically:

private void Send(Socket handler, String data)
{
    // Convert the string data to byte data using ASCII encoding.  
    byte[] byteData = Encoding.ASCII.GetBytes(data);

    // Begin sending the data to the remote device.  
    handler.BeginSend(byteData, 0, byteData.Length, 0,
                      new AsyncCallback(SendCallback), handler);
}

I would like to do it with a button.

What I have tried:

private void btnTcp1_Click(object sender, EventArgs e)
{
    string data = "";
    Socket handler;
    data = tBoxTcpSend.Text;
    byte[] byteData = Encoding.ASCII.GetBytes(data);

    handler.BeginSend(byteData, 0, byteData.Length, 0,
                      new AsyncCallback(SendCallback), handler);
}

I have tried this, but I'm getting: Use of unassigned local variable 'handler'.
I also tried to make a copy of Send method, and assign it to btnTcp1 click event, but that doesn't work either.