下面介绍一下incomingConnection
原文解释：
This virtual function is called by QTcpServer
when a new connection is available. The socketDescriptor argument is the
native socket descriptor for the accepted connection.
The base
implementation creates a QTcpSocket, sets the socket descriptor and then
stores the QTcpSocket in an internal list of pending connections.
Finally newConnection() is emitted.
Reimplement this function to alter the server’s behavior when a connection is available.
If this server is using QNetworkProxy then the socketDescriptor may not
be usable with native socket functions, and should only be used with
QTcpSocket::setSocketDescriptor().
Note: If another socket is
created in the reimplementation of this method, it needs to be added to
the Pending Connections mechanism by calling addPendingConnection().
Note: If you want to handle an incoming connection as a new QTcpSocket
object in another thread you have to pass the socketDescriptor to the
other thread and create the QTcpSocket object there and use its
setSocketDescriptor() method.
译文：
当有新的连接可用时，QTcpServer将调用这个虚拟函数。socketDescriptor参数是接受连接的本地套接字描述符。
基本实现创建一个QTcpSocket，设置套接字描述符，然后将QTcpSocket存储在一个挂起连接的内部列表中。最后发出newConnection()。
重新实现此函数，以在连接可用时更改服务器的行为。
如果此服务器使用QNetworkProxy，则socketDescriptor可能不能用于本机套接字函数，只能用于QTcpSocket::setSocketDescriptor()。
注意:如果在此方法的重新实现中创建了另一个套接字，则需要通过调用addPendingConnection()将其添加到挂起连接机制。
注意:如果您想要在另一个线程中处理一个新的QTcpSocket对象，那么您必须将socketDescriptor传递给另一个线程，并在那里创建QTcpSocket对象，然后使用它的setSocketDescriptor()方法。
