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Storing data from QnetworkReply

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  • mrjjM mrjj

    @LeeH
    Have a look at this sample
    http://www.bogotobogo.com/Qt/Qt5_Downloading_Files_QNetworkAccessManager_QNetworkRequest.php
    It uses a small helper class
    class Downloader : public QObject
    to manage the data it downloads. It responds to the finished signal.
    Here it stores to file but you can as well store in ByteArray or whatever is needed.

    Also its important to understand that you should NOT call the ReadData function yourself.
    Your function will be called when data is ready. Its an asynchronous API.

    L Offline
    L Offline
    LeeH
    wrote on last edited by LeeH
    #17

    @mrjj

    Have a look at this sample
    http://www.bogotobogo.com/Qt/Qt5_Downloading_Files_QNetworkAccessManager_QNetworkRequest.php
    It uses a small helper class
    class Downloader : public QObject
    to manage the data it downloads. It responds to the finished signal.
    Here it stores to file but you can as well store in ByteArray or whatever is needed.

    I already have a class doing this job - as I said in the begining I can already save my reply data to file that can be read/used from anywhere in one signal slot connection, I just want to do the same thing without using a file so it can be read/used from anywhere in a single connection. If my class data object that has been assigned (or appended to) the value of reply's byte array is always empty when called, say from outside of the class (after download), meaning I have to re-download everytime I need the same data, then the reply data is not stored to my object is it?

    mrjjM 1 Reply Last reply
    0
    • L LeeH

      @mrjj

      Have a look at this sample
      http://www.bogotobogo.com/Qt/Qt5_Downloading_Files_QNetworkAccessManager_QNetworkRequest.php
      It uses a small helper class
      class Downloader : public QObject
      to manage the data it downloads. It responds to the finished signal.
      Here it stores to file but you can as well store in ByteArray or whatever is needed.

      I already have a class doing this job - as I said in the begining I can already save my reply data to file that can be read/used from anywhere in one signal slot connection, I just want to do the same thing without using a file so it can be read/used from anywhere in a single connection. If my class data object that has been assigned (or appended to) the value of reply's byte array is always empty when called, say from outside of the class (after download), meaning I have to re-download everytime I need the same data, then the reply data is not stored to my object is it?

      mrjjM Offline
      mrjjM Offline
      mrjj
      Lifetime Qt Champion
      wrote on last edited by
      #18

      @LeeH said in Storing data from QnetworkReply:
      Hi
      If you keep the instance of class Downloader around,
      there is no reason you cannot keep the data for later.
      Say if you append to a QByteArray variable defined as
      class member in Downloader

      Can you please show the actual code how you use your helper class and how you later
      try to access the data?

      L 1 Reply Last reply
      0
      • mrjjM mrjj

        @LeeH said in Storing data from QnetworkReply:
        Hi
        If you keep the instance of class Downloader around,
        there is no reason you cannot keep the data for later.
        Say if you append to a QByteArray variable defined as
        class member in Downloader

        Can you please show the actual code how you use your helper class and how you later
        try to access the data?

        L Offline
        L Offline
        LeeH
        wrote on last edited by
        #19

        @mrjj said in Storing data from QnetworkReply:

        Can you please show the actual code how you use your helper class and how you later
        try to access the data?

        Certainly.

        header:

        class data : public QObject{
        
            Q_OBJECT
        
        public:
            data();
            void download();
            QByteArray get();
        
        public slots:
        
            void output(QNetworkReply* rep);
        
        private:
            QNetworkAccessManager* _qnam;
            QByteArray _ba;
        
        };
        

        source:

        data::data(){}
        
        void data::download(){
        
            _qnam = new QNetworkAccessManager(this);
            _qnam->get(QNetworkRequest(QUrl("http://www.google.com")));
            QObject::connect(_qnam, SIGNAL(finished(QNetworkReply*)), this, SLOT(output(QNetworkReply*)));
        }
        
        void data::output(QNetworkReply* rep){
        
                if(!rep->error()){
        
                   _ba.append(rep->readAll());
        
                }
                rep->deleteLater();
            }
        
        QByteArray data::get(){
            qDebug() << _ba;
        }
        

        main:

         data obj;
         obj.download();
         obj.get();
        
        jsulmJ 1 Reply Last reply
        0
        • L LeeH

          @mrjj said in Storing data from QnetworkReply:

          Can you please show the actual code how you use your helper class and how you later
          try to access the data?

          Certainly.

          header:

          class data : public QObject{
          
              Q_OBJECT
          
          public:
              data();
              void download();
              QByteArray get();
          
          public slots:
          
              void output(QNetworkReply* rep);
          
          private:
              QNetworkAccessManager* _qnam;
              QByteArray _ba;
          
          };
          

          source:

          data::data(){}
          
          void data::download(){
          
              _qnam = new QNetworkAccessManager(this);
              _qnam->get(QNetworkRequest(QUrl("http://www.google.com")));
              QObject::connect(_qnam, SIGNAL(finished(QNetworkReply*)), this, SLOT(output(QNetworkReply*)));
          }
          
          void data::output(QNetworkReply* rep){
          
                  if(!rep->error()){
          
                     _ba.append(rep->readAll());
          
                  }
                  rep->deleteLater();
              }
          
          QByteArray data::get(){
              qDebug() << _ba;
          }
          

          main:

           data obj;
           obj.download();
           obj.get();
          
          jsulmJ Offline
          jsulmJ Offline
          jsulm
          Lifetime Qt Champion
          wrote on last edited by
          #20

          @LeeH said in Storing data from QnetworkReply:

          QNetworkReply

          You should connect your output() slot to http://doc.qt.io/qt-5/qiodevice.html#readyRead signal.

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

          L 1 Reply Last reply
          2
          • jsulmJ jsulm

            @LeeH said in Storing data from QnetworkReply:

            QNetworkReply

            You should connect your output() slot to http://doc.qt.io/qt-5/qiodevice.html#readyRead signal.

            L Offline
            L Offline
            LeeH
            wrote on last edited by LeeH
            #21

            @jsulm said in Storing data from QnetworkReply:

            You should connect your output() slot to http://doc.qt.io/qt-5/qiodevice.html#readyRead signal.

            Hi

            Do you mean another connection, something like this:

            void data::download(){
            
               _qnam->get(QNetworkRequest(QUrl("http://www.google.com")));
               QObject::connect(_qnam, SIGNAL(finished(QNetworkReply*)), this, SLOT(output(QNetworkReply*)));
               QObject::connect(QIODevice, SIGNAL(readyRead()), this, SLOT(output(QNetworkReply*)));
            
            }
            

            I know the QIODevice usage here is wrong, but just trying to get an idea

            thanks

            jsulmJ 1 Reply Last reply
            0
            • L LeeH

              @jsulm said in Storing data from QnetworkReply:

              You should connect your output() slot to http://doc.qt.io/qt-5/qiodevice.html#readyRead signal.

              Hi

              Do you mean another connection, something like this:

              void data::download(){
              
                 _qnam->get(QNetworkRequest(QUrl("http://www.google.com")));
                 QObject::connect(_qnam, SIGNAL(finished(QNetworkReply*)), this, SLOT(output(QNetworkReply*)));
                 QObject::connect(QIODevice, SIGNAL(readyRead()), this, SLOT(output(QNetworkReply*)));
              
              }
              

              I know the QIODevice usage here is wrong, but just trying to get an idea

              thanks

              jsulmJ Offline
              jsulmJ Offline
              jsulm
              Lifetime Qt Champion
              wrote on last edited by
              #22

              @LeeH No need for two connections, the one for readyRead() is enough

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

              L 1 Reply Last reply
              1
              • jsulmJ jsulm

                @LeeH No need for two connections, the one for readyRead() is enough

                L Offline
                L Offline
                LeeH
                wrote on last edited by
                #23

                @jsulm

                Ok... so how should I use QIOdevice here:

                QObject::connect(QIODevice, SIGNAL(readyRead()), this, SLOT(output(QNetworkReply*)));
                

                i get error: "expecting primary expression before ',' token" and it can't be instantiated

                thanks

                m.sueM jsulmJ 2 Replies Last reply
                0
                • L LeeH

                  @jsulm

                  Ok... so how should I use QIOdevice here:

                  QObject::connect(QIODevice, SIGNAL(readyRead()), this, SLOT(output(QNetworkReply*)));
                  

                  i get error: "expecting primary expression before ',' token" and it can't be instantiated

                  thanks

                  m.sueM Offline
                  m.sueM Offline
                  m.sue
                  wrote on last edited by
                  #24

                  Hi @LeeH

                  You need the QIODevice type object not the class name there.

                  -Michael.

                  L 1 Reply Last reply
                  0
                  • m.sueM m.sue

                    Hi @LeeH

                    You need the QIODevice type object not the class name there.

                    -Michael.

                    L Offline
                    L Offline
                    LeeH
                    wrote on last edited by
                    #25

                    @m.sue

                    Hi,

                    QIODevice is an abstract class.

                    m.sueM 1 Reply Last reply
                    0
                    • L LeeH

                      @m.sue

                      Hi,

                      QIODevice is an abstract class.

                      m.sueM Offline
                      m.sueM Offline
                      m.sue
                      wrote on last edited by
                      #26

                      Hi @LeeH

                      then the object of the derived class that you use.

                      -Michael.

                      L 1 Reply Last reply
                      0
                      • m.sueM m.sue

                        Hi @LeeH

                        then the object of the derived class that you use.

                        -Michael.

                        L Offline
                        L Offline
                        LeeH
                        wrote on last edited by
                        #27

                        @m.sue said in Storing data from QnetworkReply:

                        then the object of the derived class that you use.

                        I modified my code to use readRead() from QNetworkReply object and it still doesn't work:

                        ...
                        void data::download(){
                        
                        _rep = _qnam->get(QNetworkRequest(QUrl("http://www.google.com")));
                        QObject::connect(_rep, SIGNAL(readyRead()), this, SLOT(output()));
                        
                        }
                        
                        void data::output(){
                        
                            if(!_rep->error()){
                        
                               _ba.append(_rep->readAll());
                        
                            }
                            else{
                                qDebug() << _rep->error();
                            }
                            _rep->deleteLater();
                        }
                        
                        m.sueM 1 Reply Last reply
                        0
                        • L LeeH

                          @m.sue said in Storing data from QnetworkReply:

                          then the object of the derived class that you use.

                          I modified my code to use readRead() from QNetworkReply object and it still doesn't work:

                          ...
                          void data::download(){
                          
                          _rep = _qnam->get(QNetworkRequest(QUrl("http://www.google.com")));
                          QObject::connect(_rep, SIGNAL(readyRead()), this, SLOT(output()));
                          
                          }
                          
                          void data::output(){
                          
                              if(!_rep->error()){
                          
                                 _ba.append(_rep->readAll());
                          
                              }
                              else{
                                  qDebug() << _rep->error();
                              }
                              _rep->deleteLater();
                          }
                          
                          m.sueM Offline
                          m.sueM Offline
                          m.sue
                          wrote on last edited by
                          #28

                          Hi @LeeH

                          I would write: connect(_rep, SIGNAL(readyRead()), SLOT(output())); But this should not be essential.

                          So maybe output() is not a slot.

                          -Michael.

                          L 1 Reply Last reply
                          0
                          • mrjjM Offline
                            mrjjM Offline
                            mrjj
                            Lifetime Qt Champion
                            wrote on last edited by
                            #29

                            @LeeH said in Storing data from QnetworkReply:

                            qDebug() << _rep->error();

                            Is line ever activated ?
                            is _ba.append called ?

                            L 1 Reply Last reply
                            0
                            • m.sueM m.sue

                              Hi @LeeH

                              I would write: connect(_rep, SIGNAL(readyRead()), SLOT(output())); But this should not be essential.

                              So maybe output() is not a slot.

                              -Michael.

                              L Offline
                              L Offline
                              LeeH
                              wrote on last edited by
                              #30

                              @m.sue said in Storing data from QnetworkReply:

                              So maybe output() is not a slot.

                              Hi it's always been a public slot... and i do get server reply data

                              1 Reply Last reply
                              0
                              • mrjjM mrjj

                                @LeeH said in Storing data from QnetworkReply:

                                qDebug() << _rep->error();

                                Is line ever activated ?
                                is _ba.append called ?

                                L Offline
                                L Offline
                                LeeH
                                wrote on last edited by
                                #31

                                @mrjj said in Storing data from QnetworkReply:

                                Is line ever activated ?
                                is _ba.append called ?

                                Hi, there are no errors from server, and I always get reply.
                                I call _ba from main() using data::get()

                                mrjjM 1 Reply Last reply
                                0
                                • L LeeH

                                  @mrjj said in Storing data from QnetworkReply:

                                  Is line ever activated ?
                                  is _ba.append called ?

                                  Hi, there are no errors from server, and I always get reply.
                                  I call _ba from main() using data::get()

                                  mrjjM Offline
                                  mrjjM Offline
                                  mrjj
                                  Lifetime Qt Champion
                                  wrote on last edited by
                                  #32

                                  @LeeH
                                  but is data appended?

                                  if(!_rep->error()){
                                  _ba.append(_rep->readAll());
                                  qDebug() <<"size" << _ba.size();
                                  }

                                  have you tried with a breakpoint ?
                                  is data::output() called?

                                  L 1 Reply Last reply
                                  0
                                  • mrjjM mrjj

                                    @LeeH
                                    but is data appended?

                                    if(!_rep->error()){
                                    _ba.append(_rep->readAll());
                                    qDebug() <<"size" << _ba.size();
                                    }

                                    have you tried with a breakpoint ?
                                    is data::output() called?

                                    L Offline
                                    L Offline
                                    LeeH
                                    wrote on last edited by
                                    #33

                                    @mrjj

                                    When I added:

                                    qDebug() <<"size" << _ba.size();

                                    i got:

                                    size 2634
                                    

                                    Yes data::output() is definately being called

                                    mrjjM 1 Reply Last reply
                                    0
                                    • L LeeH

                                      @mrjj

                                      When I added:

                                      qDebug() <<"size" << _ba.size();

                                      i got:

                                      size 2634
                                      

                                      Yes data::output() is definately being called

                                      mrjjM Offline
                                      mrjjM Offline
                                      mrjj
                                      Lifetime Qt Champion
                                      wrote on last edited by
                                      #34

                                      @LeeH
                                      So what is not working ?
                                      You clearly read data into _ba.

                                      L 1 Reply Last reply
                                      0
                                      • mrjjM mrjj

                                        @LeeH
                                        So what is not working ?
                                        You clearly read data into _ba.

                                        L Offline
                                        L Offline
                                        LeeH
                                        wrote on last edited by
                                        #35

                                        @mrjj

                                        but my data::get() I use to read _ba that i call from main() after downloading, is empty(""), where as if I read _ba from the slot inside the class I can see all my data

                                        L 1 Reply Last reply
                                        0
                                        • L LeeH

                                          @mrjj

                                          but my data::get() I use to read _ba that i call from main() after downloading, is empty(""), where as if I read _ba from the slot inside the class I can see all my data

                                          L Offline
                                          L Offline
                                          LeeH
                                          wrote on last edited by
                                          #36

                                          @LeeH

                                          You know I think It's best I just stick to saving to file, that seem's to be the only way I can be sure my data sticks around and can be used anywhere.... I thank everyone for their help, and apologize for wasting all of our time!

                                          A 1 Reply Last reply
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