c# BeginConnect回调在未连接时被触发

使用tcpClient.BeginConnect触发异步回调，即使没有任何客户端可以连接。然后我得到一个关于尝试.GetStream()的异常。

    public void SetupSocket() {
        try {
            tcpClient = new TcpClient();
            tcpClient.BeginConnect(host, port, ConnectCallback, tcpClient);
            Console.WriteLine("begin connect");
        }
        catch (Exception e) {
            return;
        }
    }

    private void ConnectCallback(IAsyncResult result) {
        if (OnClientEvent != null)
            OnClientEvent(this, new ClientEventArgs(Action.Connect));
        Console.WriteLine("get stream");
        stream = tcpClient.GetStream();
        Console.WriteLine("got stream");
        BeginReadAsync();
    }

输出get stream，然后关于在tcpClient连接之前尝试使用GetStream的例外。