udp通信，服务器无法获取客户端的ip [复制链接]

我的程序是这样：
udpSocket->bind(QHostAddress("192.168.20.118"), 16670);
QString ip；
connect(udpSocket, SIGNAL(readyRead()), this, SLOT(readPendingDatagram()));


void NetWork::readPendingDatagram()
{
    ip = udpSocket->peerAddress().toString();
    while(udpSocket->hasPendingDatagrams())
    {
        QByteArray datagramRecv;
        datagramRecv.resize(udpSocket->pendingDatagramSize());
        udpSocket->readDatagram(datagramRecv.data(), datagramRecv.size());
        qDebug() << (tr("接收数据: %1  %2").arg(datagramRecv.data()).arg(recvNo));
        qDebug() << (tr("IP is : %1").arg(ip));
        recvNo++;
      }
}

  ip是空的，没有数据，这是怎么回事？