Slot function not being executed in connect

[Leirbag89]

Hello
I am new here. Being looking everywhere to see if I could find an answer to my problem. So here is my problem: I am trying to make a UDP Connection and receive a video stream from a port. I have been referencing to the Qt examples with QUdpSockets and such. The problem is that the program does not seem to be going into the class slot function when I make a connection. I also have to implement this UDP connection using threads because I need to be able to constantly receive the live stream video while doing other stuff in a GUI.

Can anyone please help??

Here is my code:
UdpThread.h

#ifndef UDPTHREAD
#define UDPTHREAD
 
#include <QtCore>
#include <QHostAddress>
#include <QUdpSocket>
#include <QByteArray>
#include <QPixmap>
#include <QObject>
#include <QBuffer>
#include <QFile>
#include <QThread>
 
class QUdpSocket;
 
class UdpThread : public QObject
{
  Q_OBJECT
  public:
   UdpThread();
 
public slots:
   void run();
 
  private:
    QUdpSocket *udpSocket;
    void processTheDatagram(QByteArray);
 
  private slots:
        void readPackages();
 
};
#endif

#ifndef UDPTHREAD
#define UDPTHREAD

#include <QtCore>
#include <QHostAddress>
#include <QUdpSocket>
#include <QByteArray>
#include <QPixmap>
#include <QObject>
#include <QBuffer>
#include <QFile>
#include <QThread>

class QUdpSocket;

class UdpThread : public QObject
{
  Q_OBJECT
  public:
   UdpThread();

public slots:
   void run();

  private:
    QUdpSocket *udpSocket;
    void processTheDatagram(QByteArray);

  private slots:
        void readPackages();
	  
};
#endif

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UdpThread.cpp

#include <QtGui>
#include <QtNetwork>
#include "UdpThread.h"
 
//Constructor
UdpThread::UdpThread()
{
 
}
 
void UdpThread::run()
{
  printf("run test\n");
  udpSocket = new QUdpSocket(this);
   printf("testing 1 more time\n");
 
  udpSocket->bind(QHostAddress::LocalHost, 5555);
 
  //SLOT(readPackages())  Does not get executed
  connect(udpSocket, SIGNAL(readyRead()), this, SLOT(readPackages()), Qt::DirectConnection);
}
 
//reading data from the port
void UdpThread::readPackages()
{
  printf("before test\n"); //Never gets printed or called!
  while(udpSocket->hasPendingDatagrams())
  {
    QByteArray datagram;
    datagram.resize(udpSocket->pendingDatagramSize());
    udpSocket->readDatagram(datagram.data(), datagram.size()/**, &sender, &senderPort**/);
    printf("in while test\n");
    processTheDatagram(datagram);
  }
}
 
//display the data into an image
void UdpThread::processTheDatagram(QByteArray qba)
{
  QPixmap image;
  image.loadFromData(qba);
  image.save("test", "JPG");
  printf("file test\n");
}

#include <QtGui>
#include <QtNetwork>
#include "UdpThread.h"

//Constructor
UdpThread::UdpThread()
{

}

void UdpThread::run()
{
  printf("run test\n");
  udpSocket = new QUdpSocket(this);
   printf("testing 1 more time\n");
  
  udpSocket->bind(QHostAddress::LocalHost, 5555);
  
  //SLOT(readPackages())  Does not get executed
  connect(udpSocket, SIGNAL(readyRead()), this, SLOT(readPackages()), Qt::DirectConnection);
}

//reading data from the port
void UdpThread::readPackages()
{
  printf("before test\n"); //Never gets printed or called!
  while(udpSocket->hasPendingDatagrams())
  {
    QByteArray datagram;
    datagram.resize(udpSocket->pendingDatagramSize());
    udpSocket->readDatagram(datagram.data(), datagram.size()/**, &sender, &senderPort**/);
    printf("in while test\n");
    processTheDatagram(datagram);
  }
}

//display the data into an image
void UdpThread::processTheDatagram(QByteArray qba)
{
  QPixmap image;
  image.loadFromData(qba);
  image.save("test", "JPG");
  printf("file test\n");
}

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main.cpp

#include <QApplication>
 
#include "UdpThread.h"
 
int main(int argc, char **argv)
{
	QApplication app(argc, argv);
 
	QThread *p = new QThread;
	UdpThread *uThread = new UdpThread;
	p->start();
	uThread->moveToThread(p);
	QObject::connect(p, SIGNAL(started()), uThread, SLOT(run()));
	return app.exec();
}

#include <QApplication>

#include "UdpThread.h"

int main(int argc, char **argv)
{
	QApplication app(argc, argv);
	
	QThread *p = new QThread;
	UdpThread *uThread = new UdpThread;
	p->start();
	uThread->moveToThread(p);
	QObject::connect(p, SIGNAL(started()), uThread, SLOT(run()));
	return app.exec();
}

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Thanks for the help.

[DanH]

Well first, always test the result of connect():

bool success = connect(...);
Q_UNUSED(success);
Q_ASSERT(success);

bool success = connect(...);
Q_UNUSED(success);
Q_ASSERT(success);

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But I don't think that's your problem in this case. More likely datagrams aren't being sent to the localhost you're referencing.

[squidge]

Your thread is causing far more complexity than you need as well and is not required.

Also, don't use a QPixmap in your thread. They are for main gui thread only.

[Leirbag89]

Thanks for the replies.

DanH: I did check if connect was working before and it was returning true I just didnt included in the code because it thought it would make it to messy.

squidge: I was using QPixmap so I could save one of the datagrams into a file to see if any were being received. If I remove this will that allow the SLOT function readPackages() to work? Thats the main issue I think.

Thanks

---

Added after 31 minutes:

More likely datagrams aren't being sent to the localhost you're referencing.

-DanH

I also think this might be the problem. Is there a way to test if datagrams are being sent/received?

[Santosh Reddy]

Looks like, there is possiblity that the started() signal might have been emitted before making the connection.

so try statements in this order

//    p->start(); // remove here
    uThread->moveToThread(p);
    QObject::connect(p, SIGNAL(started()), uThread, SLOT(run()));
    p->start(); // move to here

//    p->start(); // remove here
    uThread->moveToThread(p);
    QObject::connect(p, SIGNAL(started()), uThread, SLOT(run()));
    p->start(); // move to here

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[Leirbag89]

Looks like, there is possiblity that the started() signal might have been emitted before making the connection.

so try statements in this order

//    p->start(); // remove here
    uThread->moveToThread(p);
    QObject::connect(p, SIGNAL(started()), uThread, SLOT(run()));
    p->start(); // move to here

//    p->start(); // remove here
    uThread->moveToThread(p);
    QObject::connect(p, SIGNAL(started()), uThread, SLOT(run()));
    p->start(); // move to here

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Tried... Failure... I am stumped

Thanks for replies

[Santosh Reddy]

Ok, then the only obvious reason, I can see the UPD socket is not receving any data packets, make sure data is really comming on to 127.0.0.1::5555

[squidge]

You do check the result code of udpSocket->bind I hope?

Have you confirmed the state of the socket?

If so, then you need to confirm data is arriving with a suitable network monitor.