QTcpServer(this)

[DAVC]

Hello everyone.

I have been assigned with the responsibility of maintaining some old Qt program.
In the process i had to convert it from Qt 4 to Qt 5.10 and from Qwt 4.x.x to Qwt 6.1.3

Everything seemed to work and i can compile and run the program.
However, when the server is set up to listen on the corresponding ports, new_Connection() is never called.

I get the following warning:

QObject: Cannot create children for a parent that is in a different thread.
(Parent is gui::model::Listener(0x2ba442c0), parent's thread is QThread(0x215f97b8), current thread is QThread(0x2ba445b0)

More specifically (see code below) the line

server_ = new QTcpServer(this);

server_ = new QTcpServer(this);

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is causing it.
I have a strong feeling that it's because

Listener

Listener

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is not in the same thread as

server_

server_

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I have search the internet thin, but I cannot seem to find any post that has relevance (or they are too old)

#include <QtNetwork>
#include <QtDebug>
#include "listener.h"
#include "sockethandler.h"
#include <qthread.h>
 
// Assertion to ensure that char and short has the expected sizes
// (required for protocol to work)
 
namespace gui { namespace model {
   Listener::Listener(QObject *parent, int port) :
         QObject(parent), port_(port), server_(0)
   { }
 
   /**
     * Create server and listen for connections
     */
   void Listener::listen() {
      if (server_!=0) qFatal("listen() called on a connection that was already initialized");
      server_ = new QTcpServer(this);
      server_->listen(QHostAddress::Any, port_);
      qDebug() << connect(server_, SIGNAL(newConnection()),
              this, SLOT(new_Connection()));
      emit log(tr("Listening on port %1").arg(port_));
   }
 
   /**
     * Called on new connection.
     * Check for duplicate and initialize socket.
     */
   void Listener::new_Connection()
   {
      while (server_->hasPendingConnections()) {
         emit log(tr("Connection opened on port %1").arg(port_));
         emit connected(
               new SocketHandler(this, server_->nextPendingConnection())
               );
      }
   }
}} // gui::model

#include <QtNetwork>
#include <QtDebug>
#include "listener.h"
#include "sockethandler.h"
#include <qthread.h>

// Assertion to ensure that char and short has the expected sizes
// (required for protocol to work)

namespace gui { namespace model {
   Listener::Listener(QObject *parent, int port) :
         QObject(parent), port_(port), server_(0)
   { }

   /**
     * Create server and listen for connections
     */
   void Listener::listen() {
      if (server_!=0) qFatal("listen() called on a connection that was already initialized");
      server_ = new QTcpServer(this);
      server_->listen(QHostAddress::Any, port_);
      qDebug() << connect(server_, SIGNAL(newConnection()),
              this, SLOT(new_Connection()));
      emit log(tr("Listening on port %1").arg(port_));
   }

   /**
     * Called on new connection.
     * Check for duplicate and initialize socket.
     */
   void Listener::new_Connection()
   {
      while (server_->hasPendingConnections()) {
         emit log(tr("Connection opened on port %1").arg(port_));
         emit connected(
               new SocketHandler(this, server_->nextPendingConnection())
               );
      }
   }
}} // gui::model

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Writing

server_ = new QTcpServer();

server_ = new QTcpServer();

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instead of

server_ = new QTcpServer(this);

server_ = new QTcpServer(this);

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removes the warning, but the problem persists.

.h file:

#ifndef CONNECTION_H
#define CONNECTION_H
 
#include <QObject>
 
#include "connectassert.h"
 
QT_BEGIN_NAMESPACE
class QTcpServer;
class QTcpSocket;
QT_END_NAMESPACE
 
namespace gui { namespace model {
   class SocketHandler;
   /**
    * Listens on a single port for a connection from HAsim.
    */
   class Listener : public QObject {
      Q_OBJECT
   public:
      /** Creates object */
      explicit Listener(QObject *parent, int port);
      /** Listens for connections */
      void listen();
 
   signals:
      /** Emitted when a connection is opened */
      void connected(SocketHandler*);
      /** Emitted when there is information available about connection */
      void log(QString str);
 
   private slots:
      void new_Connection();
 
   private:
      int port_;
 
      QTcpServer *server_;
   };
 
}} // gui::model
 
#endif // CONNECTION_H

#ifndef CONNECTION_H
#define CONNECTION_H

#include <QObject>

#include "connectassert.h"

QT_BEGIN_NAMESPACE
class QTcpServer;
class QTcpSocket;
QT_END_NAMESPACE

namespace gui { namespace model {
   class SocketHandler;
   /**
    * Listens on a single port for a connection from HAsim.
    */
   class Listener : public QObject {
      Q_OBJECT
   public:
      /** Creates object */
      explicit Listener(QObject *parent, int port);
      /** Listens for connections */
      void listen();

   signals:
      /** Emitted when a connection is opened */
      void connected(SocketHandler*);
      /** Emitted when there is information available about connection */
      void log(QString str);

   private slots:
      void new_Connection();

   private:
      int port_;

      QTcpServer *server_;
   };

}} // gui::model

#endif // CONNECTION_H

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So how can I correctly fix the error?

EDIT: I forgot to add - This worked before (on Qt4), so what is changed from Qt4 to Qt5.10 that would cause this to fail?

I hope you can help

best regards
David