qt5base-lts/examples/network/multicastreceiver/receiver.cpp

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#include <QtWidgets>
#include <QtNetwork>

#include "receiver.h"

Receiver::Receiver(QWidget *parent)
    : QDialog(parent)
{
    groupAddress = QHostAddress("239.255.43.21");

    statusLabel = new QLabel(tr("Listening for multicasted messages"));
    quitButton = new QPushButton(tr("&Quit"));

    udpSocket = new QUdpSocket(this);
    udpSocket->bind(QHostAddress::AnyIPv4, 45454, QUdpSocket::ShareAddress);
    udpSocket->joinMulticastGroup(groupAddress);

    connect(udpSocket, SIGNAL(readyRead()),
            this, SLOT(processPendingDatagrams()));
    connect(quitButton, SIGNAL(clicked()), this, SLOT(close()));

    QHBoxLayout *buttonLayout = new QHBoxLayout;
    buttonLayout->addStretch(1);
    buttonLayout->addWidget(quitButton);
    buttonLayout->addStretch(1);

    QVBoxLayout *mainLayout = new QVBoxLayout;
    mainLayout->addWidget(statusLabel);
    mainLayout->addLayout(buttonLayout);
    setLayout(mainLayout);

    setWindowTitle(tr("Multicast Receiver"));
}

void Receiver::processPendingDatagrams()
{
    while (udpSocket->hasPendingDatagrams()) {
        QByteArray datagram;
        datagram.resize(udpSocket->pendingDatagramSize());
        udpSocket->readDatagram(datagram.data(), datagram.size());
        statusLabel->setText(tr("Received datagram: \"%1\"")
                             .arg(datagram.data()));
    }
}