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First attempt to use Qt networking on QML apps

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  • jsulmJ jsulm

    @qcoderpro said in First attempt to use Qt networking on QML apps:

    So I cut that connection there and pasted it in the initServer(). Still theonNewConnectionis not called!

    Please show your current code

    Q Offline
    Q Offline
    qcoderpro
    wrote on last edited by
    #18

    @jsulm

    This is code for server.cpp:

    #include "server.h"
    #include <QtNetwork>
    #include <QtCore>
    
    Server::Server(QObject *parent) : QObject{parent}
        , tcpServer(new QTcpServer(this)) { }
    
    QString Server::initServer() {
        // Called from the front-end
    
        tcpServer = new QTcpServer(this);
        if(!tcpServer->listen())
            return "Server Unable to start the server: " +
                    tcpServer->errorString();
    
        QString ipAddress;
        QList<QHostAddress> ipAddressesList = QNetworkInterface::allAddresses();
    
        // use the first non-local IPv4 address
        for(int i=0; i<ipAddressesList.size(); ++i)
            if(ipAddressesList.at(i) != QHostAddress::LocalHost &&
                    ipAddressesList.at(i).toIPv4Address()) {
                ipAddress = ipAddressesList.at(i).toString();
                break;
            }
    
        // if we did not find one, use IPv4 localhost
        if(ipAddress.isEmpty())
            ipAddress = QHostAddress(QHostAddress::LocalHost).toString();
    
        return " The server is running on\n\n IP: " +
                ipAddress + "\n port: " + QString::number(tcpServer->serverPort())
                + "\n\n Run the Client example now.";
        connect(tcpServer, &QTcpServer::newConnection, this, &Server::onNewConnection);
    }
    
    void Server::onNewConnection()
    {
        qDebug() << "OnNewConnection was called!\n";
    
        QTcpSocket *clientConnection = tcpServer->nextPendingConnection();
        connect(clientConnection, &QAbstractSocket::disconnected,
                clientConnection, &QObject::deleteLater);
        in.setDevice(clientConnection);
        in.setVersion(QDataStream::Qt_4_0);
        connect(clientConnection, &QAbstractSocket::readyRead, this, &Server::setMessage);
    }
    
    void Server::setMessage()
    {
        in.startTransaction();
    
        QString msg;
        in >> msg;
    
        if (!in.commitTransaction())
            message = "commitTransaction error" ;
        else
            message = msg;
    }
    
    QString Server::getMessage() const
    {
        return message;
    }
    

    Totally there're 6 files as follows:
    server.h, server.cpp, server qml file, client.h, client.cpp and client qml file

    If you like I can pack them all in a zip file and send it to a global resource for freely downloading and consideration.

    jsulmJ 1 Reply Last reply
    0
    • Q qcoderpro

      @jsulm

      This is code for server.cpp:

      #include "server.h"
      #include <QtNetwork>
      #include <QtCore>
      
      Server::Server(QObject *parent) : QObject{parent}
          , tcpServer(new QTcpServer(this)) { }
      
      QString Server::initServer() {
          // Called from the front-end
      
          tcpServer = new QTcpServer(this);
          if(!tcpServer->listen())
              return "Server Unable to start the server: " +
                      tcpServer->errorString();
      
          QString ipAddress;
          QList<QHostAddress> ipAddressesList = QNetworkInterface::allAddresses();
      
          // use the first non-local IPv4 address
          for(int i=0; i<ipAddressesList.size(); ++i)
              if(ipAddressesList.at(i) != QHostAddress::LocalHost &&
                      ipAddressesList.at(i).toIPv4Address()) {
                  ipAddress = ipAddressesList.at(i).toString();
                  break;
              }
      
          // if we did not find one, use IPv4 localhost
          if(ipAddress.isEmpty())
              ipAddress = QHostAddress(QHostAddress::LocalHost).toString();
      
          return " The server is running on\n\n IP: " +
                  ipAddress + "\n port: " + QString::number(tcpServer->serverPort())
                  + "\n\n Run the Client example now.";
          connect(tcpServer, &QTcpServer::newConnection, this, &Server::onNewConnection);
      }
      
      void Server::onNewConnection()
      {
          qDebug() << "OnNewConnection was called!\n";
      
          QTcpSocket *clientConnection = tcpServer->nextPendingConnection();
          connect(clientConnection, &QAbstractSocket::disconnected,
                  clientConnection, &QObject::deleteLater);
          in.setDevice(clientConnection);
          in.setVersion(QDataStream::Qt_4_0);
          connect(clientConnection, &QAbstractSocket::readyRead, this, &Server::setMessage);
      }
      
      void Server::setMessage()
      {
          in.startTransaction();
      
          QString msg;
          in >> msg;
      
          if (!in.commitTransaction())
              message = "commitTransaction error" ;
          else
              message = msg;
      }
      
      QString Server::getMessage() const
      {
          return message;
      }
      

      Totally there're 6 files as follows:
      server.h, server.cpp, server qml file, client.h, client.cpp and client qml file

      If you like I can pack them all in a zip file and send it to a global resource for freely downloading and consideration.

      jsulmJ Online
      jsulmJ Online
      jsulm
      Lifetime Qt Champion
      wrote on last edited by
      #19

      @qcoderpro said in First attempt to use Qt networking on QML apps:

      ipAddress = ipAddressesList.at(i).toString();

      What is ipAddress used for? You are not using it when you call listen().

      But the actuall issue is that you have a return just before connect(), so connect() is never called...

      https://forum.qt.io/topic/113070/qt-code-of-conduct

      Q 1 Reply Last reply
      2
      • jsulmJ jsulm

        @qcoderpro said in First attempt to use Qt networking on QML apps:

        ipAddress = ipAddressesList.at(i).toString();

        What is ipAddress used for? You are not using it when you call listen().

        But the actuall issue is that you have a return just before connect(), so connect() is never called...

        Q Offline
        Q Offline
        qcoderpro
        wrote on last edited by
        #20

        @jsulm

        What is ipAddress used for? You are not using it when you call listen().

        ipAddress is used to store the list of local/non-local IP addresses. But I didn't understand the part "You are not using it when you call listen()".

        But the actuall issue is that you have a return just before connect(), so connect() is never called..

        Right. I moved the connect() to the part right after the listen(). Now the onNewConnection() slot is successfully called and it prints the message "OnNewConnection was called" in Application Output window as expected.

        Now there's still a problem remaining!
        This is client.cpp:

        #include "client.h"
        #include <QtNetwork>
        
        Client::Client(QObject *parent)
            : QObject{parent}
            , tcpSocket(new QTcpSocket(this))
        {
            out.setDevice(tcpSocket);
            out.setVersion(QDataStream::Qt_4_0);
        }
        
        void Client::sendAddress(QString ip, QString port)
        {
            tcpSocket->abort();
            tcpSocket->connectToHost(ip, port.toInt());
        
            connect(tcpSocket, &QAbstractSocket::connected, []() {
                qDebug() << "Connected to the host";
            });
        }
        
        void Client::sendMessage(const QString& message)
        //called from front-end
        {
            QByteArray block;
            QDataStream out(&block, QIODevice::WriteOnly);
            out.setVersion(QDataStream::Qt_5_10);
            out << message;
            tcpSocket->write(block);
        }
        

        The sendAddress slot prints the message of the lambda in output ("Connected to the host") so by that I assume the connection between the client and server the way above is properly established. The remaining problem is that the sendMessage slot still doesn't send its message (its string parameter) to the sever! :(

        jsulmJ 1 Reply Last reply
        0
        • Q qcoderpro

          @jsulm

          What is ipAddress used for? You are not using it when you call listen().

          ipAddress is used to store the list of local/non-local IP addresses. But I didn't understand the part "You are not using it when you call listen()".

          But the actuall issue is that you have a return just before connect(), so connect() is never called..

          Right. I moved the connect() to the part right after the listen(). Now the onNewConnection() slot is successfully called and it prints the message "OnNewConnection was called" in Application Output window as expected.

          Now there's still a problem remaining!
          This is client.cpp:

          #include "client.h"
          #include <QtNetwork>
          
          Client::Client(QObject *parent)
              : QObject{parent}
              , tcpSocket(new QTcpSocket(this))
          {
              out.setDevice(tcpSocket);
              out.setVersion(QDataStream::Qt_4_0);
          }
          
          void Client::sendAddress(QString ip, QString port)
          {
              tcpSocket->abort();
              tcpSocket->connectToHost(ip, port.toInt());
          
              connect(tcpSocket, &QAbstractSocket::connected, []() {
                  qDebug() << "Connected to the host";
              });
          }
          
          void Client::sendMessage(const QString& message)
          //called from front-end
          {
              QByteArray block;
              QDataStream out(&block, QIODevice::WriteOnly);
              out.setVersion(QDataStream::Qt_5_10);
              out << message;
              tcpSocket->write(block);
          }
          

          The sendAddress slot prints the message of the lambda in output ("Connected to the host") so by that I assume the connection between the client and server the way above is properly established. The remaining problem is that the sendMessage slot still doesn't send its message (its string parameter) to the sever! :(

          jsulmJ Online
          jsulmJ Online
          jsulm
          Lifetime Qt Champion
          wrote on last edited by
          #21

          @qcoderpro said in First attempt to use Qt networking on QML apps:

          But I didn't understand the part "You are not using it when you call listen()".

          You know that you can pass an IP to listen? See https://doc.qt.io/qt-5/qtcpserver.html#listen

          Where and when do you call sendMessage ?
          You also should add code for error handling: https://doc.qt.io/qt-5/qabstractsocket.html#errorOccurred
          https://doc.qt.io/qt-5/qiodevice.html#errorString

          https://forum.qt.io/topic/113070/qt-code-of-conduct

          Q 1 Reply Last reply
          0
          • jsulmJ jsulm

            @qcoderpro said in First attempt to use Qt networking on QML apps:

            But I didn't understand the part "You are not using it when you call listen()".

            You know that you can pass an IP to listen? See https://doc.qt.io/qt-5/qtcpserver.html#listen

            Where and when do you call sendMessage ?
            You also should add code for error handling: https://doc.qt.io/qt-5/qabstractsocket.html#errorOccurred
            https://doc.qt.io/qt-5/qiodevice.html#errorString

            Q Offline
            Q Offline
            qcoderpro
            wrote on last edited by qcoderpro
            #22

            @jsulm

            You know that you can pass an IP to listen? See https://doc.qt.io/qt-5/qtcpserver.html#listen

            No, I didn't know that and if I use listen() that way I need to someway convert the ipAddress which a QString to a QHostAddress. But now the connection is properly established and the connect(...) calls the slot onNewConnection.

            Where and when do you call sendMessage ?

            In the front-end:

             ColumnLayout {
                    anchors.fill: parent
            
                    TextField {
                        id: ipAddrs
                    }
                    TextField {
                            id: portNum
                        }
                    Button {
                        text: "Send Address"
                        onClicked: myObj.sendAddress(ipAddrs.text.toString(), portNum.text.toString())
                    }
            
                    RowLayout {
                        Layout.alignment: Qt.AlignBottom
            
                        TextField {
                            id: txtField
                            Layout.fillWidth: true
                        }
                        Button {
                            text: qsTr("Send")
                            onClicked: myObj.sendMessage(txtField.text)
                        }
                    }
                }
            
                MyClass {
                    id: myObj
                }
            

            wqerwr.PNG

            You also should add code for error handling: https://doc.qt.io/qt-5/qabstractsocket.html#errorOccurred
            https://doc.qt.io/qt-5/qiodevice.html#errorString

            For that, I added this connect() after the lambda in client.cpp:
            connect(tcpSocket, &QAbstractSocket::errorOccurred, this, &Client::displayError); and this slot there:

            void Client::displayError(QAbstractSocket::SocketError socketError) {
               // for this stage, printing the error messages using qDenug will be fine
            
                switch (socketError) {
                case QAbstractSocket::RemoteHostClosedError:
                    break;
                case QAbstractSocket::HostNotFoundError:
                    qDebug() <<"The host was not found. Please check the "
                               "host name and port settings.";
                    break;
                case QAbstractSocket::ConnectionRefusedError:
                    qDebug() << "The connection was refused by the peer. "
                                "Make sure the server is running, "
                                "and check that the host name and port "
                                "settings are correct.";
                    break;
                default:
                    qDebug() << "The following error occurred: " + tcpSocket->errorString();
                }
            }
            

            Still no message is sent nor there's any error.

            jsulmJ 1 Reply Last reply
            0
            • Q qcoderpro

              @jsulm

              You know that you can pass an IP to listen? See https://doc.qt.io/qt-5/qtcpserver.html#listen

              No, I didn't know that and if I use listen() that way I need to someway convert the ipAddress which a QString to a QHostAddress. But now the connection is properly established and the connect(...) calls the slot onNewConnection.

              Where and when do you call sendMessage ?

              In the front-end:

               ColumnLayout {
                      anchors.fill: parent
              
                      TextField {
                          id: ipAddrs
                      }
                      TextField {
                              id: portNum
                          }
                      Button {
                          text: "Send Address"
                          onClicked: myObj.sendAddress(ipAddrs.text.toString(), portNum.text.toString())
                      }
              
                      RowLayout {
                          Layout.alignment: Qt.AlignBottom
              
                          TextField {
                              id: txtField
                              Layout.fillWidth: true
                          }
                          Button {
                              text: qsTr("Send")
                              onClicked: myObj.sendMessage(txtField.text)
                          }
                      }
                  }
              
                  MyClass {
                      id: myObj
                  }
              

              wqerwr.PNG

              You also should add code for error handling: https://doc.qt.io/qt-5/qabstractsocket.html#errorOccurred
              https://doc.qt.io/qt-5/qiodevice.html#errorString

              For that, I added this connect() after the lambda in client.cpp:
              connect(tcpSocket, &QAbstractSocket::errorOccurred, this, &Client::displayError); and this slot there:

              void Client::displayError(QAbstractSocket::SocketError socketError) {
                 // for this stage, printing the error messages using qDenug will be fine
              
                  switch (socketError) {
                  case QAbstractSocket::RemoteHostClosedError:
                      break;
                  case QAbstractSocket::HostNotFoundError:
                      qDebug() <<"The host was not found. Please check the "
                                 "host name and port settings.";
                      break;
                  case QAbstractSocket::ConnectionRefusedError:
                      qDebug() << "The connection was refused by the peer. "
                                  "Make sure the server is running, "
                                  "and check that the host name and port "
                                  "settings are correct.";
                      break;
                  default:
                      qDebug() << "The following error occurred: " + tcpSocket->errorString();
                  }
              }
              

              Still no message is sent nor there's any error.

              jsulmJ Online
              jsulmJ Online
              jsulm
              Lifetime Qt Champion
              wrote on last edited by
              #23

              @qcoderpro said in First attempt to use Qt networking on QML apps:

              For that, I added this connect() after the lambda in client.cpp:

              The idea was actually to check the errors on server side

              https://forum.qt.io/topic/113070/qt-code-of-conduct

              Q 1 Reply Last reply
              1
              • jsulmJ jsulm

                @qcoderpro said in First attempt to use Qt networking on QML apps:

                For that, I added this connect() after the lambda in client.cpp:

                The idea was actually to check the errors on server side

                Q Offline
                Q Offline
                qcoderpro
                wrote on last edited by
                #24

                @jsulm
                Yeah, right.
                I declared a QTcpSocket object in the server app and added the connect() and displayError slot as mentioned above in it. As before, the connection is established but no message is sent nor is an error displayed!
                I shared both projects in a zip file in link below. If you have time, take a look at them please. I'm sure the remaining problem will be clear to you. I tried to keep the projects as simple as possible just to do the job: https://www.4shared.com/s/f_Gct6Kjwiq

                1 Reply Last reply
                0
                • GrecKoG Offline
                  GrecKoG Offline
                  GrecKo
                  Qt Champions 2018
                  wrote on last edited by
                  #25

                  This file sharing is unusable without account it seems.

                  If you want to share multiple files, using https://gist.github.com would be better for the people that want to help you.

                  Q 1 Reply Last reply
                  1
                  • GrecKoG GrecKo

                    This file sharing is unusable without account it seems.

                    If you want to share multiple files, using https://gist.github.com would be better for the people that want to help you.

                    Q Offline
                    Q Offline
                    qcoderpro
                    wrote on last edited by
                    #26

                    @GrecKo
                    That's a code sharing platform (instead of files) but if code is meant to be easier than the projects both in a zip file then as usual it's feasible to share them here.
                    server.h:

                    #include <QObject>
                    #include <QAbstractSocket>
                    
                    class QTcpServer;
                    class QTcpSocket;
                    
                    class Server : public QObject
                    {
                        Q_OBJECT
                    public:
                        explicit Server(QObject *parent = nullptr);
                    
                    public slots:
                        QString initServer();
                        void setMessage();
                        QString getMessage() const;
                        void onNewConnection();
                        void displayError(QAbstractSocket::SocketError);
                    
                    private:
                        QTcpServer* tcpServer { nullptr };
                        QTcpSocket* tcpSocket { nullptr };
                        QDataStream in;
                        QString message;
                    };
                    

                    server.cpp:

                    #include "server.h"
                    #include <QtNetwork>
                    #include <QtCore>
                    
                    Server::Server(QObject *parent) : QObject{parent}
                        , tcpServer(new QTcpServer(this))
                        , tcpSocket(new QTcpSocket(this)) { }
                    
                    QString Server::initServer() {
                        // Called from the front-end
                    
                        tcpServer = new QTcpServer(this);
                        if(!tcpServer->listen())
                            return "Server Unable to start the server: " +
                                    tcpServer->errorString();
                    
                        connect(tcpServer, &QTcpServer::newConnection, this, &Server::onNewConnection);
                        connect(tcpSocket, &QAbstractSocket::errorOccurred, this, &Server::displayError);
                    
                        QString ipAddress;
                        QList<QHostAddress> ipAddressesList = QNetworkInterface::allAddresses();
                    
                        // use the first non-local IPv4 address
                        for(int i=0; i<ipAddressesList.size(); ++i)
                            if(ipAddressesList.at(i) != QHostAddress::LocalHost &&
                                    ipAddressesList.at(i).toIPv4Address()) {
                                ipAddress = ipAddressesList.at(i).toString();
                                break;
                            }
                    
                        // if we did not find one, use IPv4 localhost
                        if(ipAddress.isEmpty())
                            ipAddress = QHostAddress(QHostAddress::LocalHost).toString();
                    
                        return " The server is running on\n\n IP: " +
                                ipAddress + "\n port: " + QString::number(tcpServer->serverPort())
                                + "\n\n Run the Client example now.";
                    }
                    
                    void Server::onNewConnection()
                    {
                        qDebug() << "OnNewConnection was called!\n";
                    
                        QTcpSocket *clientConnection = tcpServer->nextPendingConnection();
                        connect(clientConnection, &QAbstractSocket::disconnected,
                                clientConnection, &QObject::deleteLater);
                        in.setDevice(clientConnection);
                        in.setVersion(QDataStream::Qt_4_0);
                        connect(clientConnection, &QAbstractSocket::readyRead, this, &Server::setMessage);
                    }
                    
                    void Server::displayError(QAbstractSocket::SocketError socketError)
                    {
                        // for this stage, printing the error messages using qDenug will be fine
                    
                         switch (socketError) {
                         case QAbstractSocket::RemoteHostClosedError:
                             break;
                         case QAbstractSocket::HostNotFoundError:
                             qDebug() <<"The host was not found. Please check the "
                                        "host name and port settings.";
                             break;
                         case QAbstractSocket::ConnectionRefusedError:
                             qDebug() << "The connection was refused by the peer. "
                                         "Make sure the server is running, "
                                         "and check that the host name and port "
                                         "settings are correct.";
                             break;
                         default:
                             qDebug() << "The following error occurred: " + tcpSocket->errorString();
                         }
                    }
                    
                    void Server::setMessage()
                    {
                        in.startTransaction();
                    
                        QString msg;
                        in >> msg;
                    
                        if (!in.commitTransaction())
                            message = "commitTransaction error" ;
                        else
                            message = msg;
                    }
                    
                    QString Server::getMessage() const
                    {
                        return message;
                    }
                    

                    server's project qml file:

                    import QtQuick
                    import QtQuick.Controls
                    import QtQuick.Layouts
                    import SomeClass 1.0
                    
                    Window {
                        width: 300
                        height: 200
                        visible: true
                        title: qsTr("Server")
                        color: "lightblue"
                    
                        ColumnLayout {
                            anchors.fill: parent
                    
                            Label {
                                text: myObj.initServer()
                            }
                    
                            Label {
                                id: msgLabel
                                text: myObj.getMessage()
                            }
                        }
                    
                        MyClass {
                            id: myObj
                        }
                    }
                    

                    client.h:

                    #include <QDataStream>
                    #include <QObject>
                    
                    class QTcpSocket;
                    
                    class Client : public QObject
                    {
                        Q_OBJECT
                    
                    public:
                        explicit Client(QObject *parent = nullptr);
                    
                    public slots:
                        void sendAddress(QString, QString);
                        void sendMessage(const QString&);
                    
                    private:
                        QTcpSocket* tcpSocket { nullptr };
                        QDataStream out;
                    };
                    

                    client.cpp:

                    #include "client.h"
                    #include <QtNetwork>
                    
                    Client::Client(QObject *parent)
                        : QObject{parent}
                        , tcpSocket(new QTcpSocket(this))
                    {
                        out.setDevice(tcpSocket);
                        out.setVersion(QDataStream::Qt_4_0);
                    }
                    
                    void Client::sendAddress(QString ip, QString port)
                    {
                        tcpSocket->abort();
                        tcpSocket->connectToHost(ip, port.toInt());
                    
                        connect(tcpSocket, &QAbstractSocket::connected, []() {
                            qDebug() << "Connected to the host";
                        });
                    }
                    
                    void Client::sendMessage(const QString& message) {
                          //called from front-end
                        QByteArray block;
                        QDataStream out(&block, QIODevice::WriteOnly);
                        out.setVersion(QDataStream::Qt_5_10);
                        out << message;
                        tcpSocket->write(block);
                    }
                    

                    client's project qml file:

                    import QtQuick
                    import QtQuick.Controls
                    import QtQuick.Layouts
                    import SomeClass 1.0
                    
                    Window {
                        width: 300
                        height: 200
                        visible: true
                        title: qsTr("Client")
                        color: "lightblue"
                    
                        ColumnLayout {
                            anchors.fill: parent
                    
                            TextField {
                                id: ipAddrs
                            }
                            TextField {
                                    id: portNum
                                }
                            Button {
                                text: "Send Address"
                                onClicked: myObj.sendAddress(ipAddrs.text.toString(), portNum.text.toString())
                            }
                    
                            RowLayout {
                                Layout.alignment: Qt.AlignBottom
                    
                                TextField {
                                    id: txtField
                                    Layout.fillWidth: true
                                }
                                Button {
                                    text: qsTr("Send")
                                    onClicked: myObj.sendMessage(txtField.text)
                                }
                            }
                        }
                    
                        MyClass {
                            id: myObj
                        }
                    }
                    

                    Hopefully we can now find the issue. :(

                    1 Reply Last reply
                    0
                    • Q Offline
                      Q Offline
                      qcoderpro
                      wrote on last edited by
                      #27

                      Here is also the link for that platform embracing the files code: https://gist.github.com/Tomtesty/eff99a9721afa7a44558fe097e65b079

                      1 Reply Last reply
                      0
                      • Q Offline
                        Q Offline
                        qcoderpro
                        wrote on last edited by
                        #28

                        Is the problem still ambiguous, please? I tried hard but can't find the issue. :(

                        1 Reply Last reply
                        0

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