I need to broadcast an udp packet on all network interfaces, using only QIODevice methods (QIODevice::write() and no QUDPSocket::writeDatagram()), apart from connetcing and binding.

I also have upgraded to qt 5.6 due to qt bug #26538.

A simplified example is as follows:
Qt Code: 
  1. class Dialog : public QDialog
  2. {
  3.     Q_OBJECT
  4.  
  5. public:
  6.     explicit Dialog(QWidget *parent = 0);
  7.     ~Dialog();
  8.  
  9. private:
  10.     Ui::Dialog *ui;
  11.     QUdpSocket *sock;
  12.  
  13. public slots:
  14.     void onReadyRead(void);
  15.     void onButtonClicked(void);
  16. };
  17.  
  18. #define USE_QIODEVICE  // remove this define to use QUDPSocket methods
  19.  
  20. Dialog::Dialog(QWidget *parent) :
  21.     QDialog(parent),
  22.     ui(new Ui::Dialog)
  23. {
  24.     ui->setupUi(this);
  25.  
  26.     connect(ui->pushBtn,SIGNAL(clicked()), this, SLOT(onButtonClicked()));
  27.  
  28.     qDebug() << qVersion();
  29.  
  30.     sock = new QUdpSocket(this);
  31.     connect(sock, &QUdpSocket::readyRead, this, &Dialog::onReadyRead);
  32.  
  33. #if !defined(USE_QIODEVICE)
  34.     sock->bind();
  35.     qDebug() << sock->localPort();
  36. #endif
  37. }
  38.  
  39. void Dialog::onButtonClicked(void)
  40. {
  41.     QList<QNetworkInterface> list = QNetworkInterface::allInterfaces();
  42.     foreach (QNetworkInterface iface, list)
  43.     {
  44.         QList<QNetworkAddressEntry> AEList = iface.addressEntries();
  45.         foreach(QNetworkAddressEntry AE, AEList)
  46.         {
  47.             if(AE.broadcast().protocol() == QAbstractSocket::IPv4Protocol)
  48.             {
  49. #if defined(USE_QIODEVICE)
  50.                 sock->bind(54366); // I have to call bind() for every interface because disconnectFromHost() unbind
  51.                 sock->connectToHost(AE.broadcast(), 44444);  // I have to call connectToHost to make the subsequent call to write() works
  52.                 qDebug() << sock->localPort();
  53.                 sock->write("hallo");
  54.                 sock->disconnectFromHost(); // I have to call disconnectFromHost() otherwise the subsequent call to connectToHost() will fail
  55. #else
  57.                 dg = "hallo";
  58.                 sock->writeDatagram(dg,AE.broadcast(), 44444);
  59. #endif
  60.                 qDebug() << "send to" << AE.broadcast();
  61.             }
  62.         }
  63.     }
  64. }
  65.  
  66. void Dialog::onReadyRead(void)
  67. {
  68. #if defined(USE_QIODEVICE)
  70.  
  71.     qDebug() << "received";
  72.     ba = sock->readAll();
  73. #else
  74.     char data[64];
  76.     quint16 port;
  77.  
  78.     while(sock->hasPendingDatagrams())
  79.     {
  80.         sock->readDatagram(data, sizeof(data), &host, &port);
  81.         qDebug() << "received";
  82.     }
  83.  
  84. #endif
  85. // data processing...
  86. }
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Unfortunately this code doesn't works because when the replies come back from the hosts the interface is (probably already) unbound, and onReadyRead() is never called.

When I remove definition of USE_QIODEVICE the QUDPSocket methods are used instead of QIODevice.
In this way all seems to work.

How can I get the wanted behaviour using only QIODevice methods (apart from connetcing and binding)?

Best regards
Max