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signal/slot between two different classes

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  • D dziko147

    @jsulm be sure that I tried to recover on my own . if you can't/do not want help me ,please ignore this topic :)

    jsulmJ Offline
    jsulmJ Offline
    jsulm
    Lifetime Qt Champion
    wrote on last edited by
    #4

    @dziko147 said in signal/slot between two different classes:

    be sure that I tried to recover on my own

    Then please show what you tried and say what went wrong if you want to get meaningful help...

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

    D 1 Reply Last reply
    0
    • jsulmJ jsulm

      @dziko147 said in signal/slot between two different classes:

      be sure that I tried to recover on my own

      Then please show what you tried and say what went wrong if you want to get meaningful help...

      D Offline
      D Offline
      dziko147
      wrote on last edited by dziko147
      #5

      @jsulm ok I tried this actually

      in //MainWindow.h

      signals:
          void canDeviceChanged(int value);
      

      in //MainWindow.cpp

      connect(this, SIGNAL(canDeviceChanged(int value )),&back, SLOT(statuspican(int value)));
      
      
      if (m_canDevice)
          emit canDeviceChanged(1); 
      

      in backend.h

      public slots:
          void statuspican(int value);
      

      in backend.cpp

      void Backend::statuspican(int value)
      {
      qDebug() << "from Mainwindow :" << value;
      }
      
      KroMignonK jsulmJ 2 Replies Last reply
      0
      • D dziko147

        @jsulm ok I tried this actually

        in //MainWindow.h

        signals:
            void canDeviceChanged(int value);
        

        in //MainWindow.cpp

        connect(this, SIGNAL(canDeviceChanged(int value )),&back, SLOT(statuspican(int value)));
        
        
        if (m_canDevice)
            emit canDeviceChanged(1); 
        

        in backend.h

        public slots:
            void statuspican(int value);
        

        in backend.cpp

        void Backend::statuspican(int value)
        {
        qDebug() << "from Mainwindow :" << value;
        }
        
        KroMignonK Offline
        KroMignonK Offline
        KroMignon
        wrote on last edited by KroMignon
        #6

        @dziko147 said in signal/slot between two different classes:

        connect(this, SIGNAL(canDeviceChanged(int value )),&back, SLOT(statuspican2(int value)));

        Have you read the link a give you at least 5 times?
        This can not work ==> https://doc.qt.io/qt-5/qobject.html#connect

        EDIT
        What is statuspican2?
        According to your code, the slot name is statuspican

        It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth. (Sherlock Holmes)

        1 Reply Last reply
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        • D dziko147

          @jsulm ok I tried this actually

          in //MainWindow.h

          signals:
              void canDeviceChanged(int value);
          

          in //MainWindow.cpp

          connect(this, SIGNAL(canDeviceChanged(int value )),&back, SLOT(statuspican(int value)));
          
          
          if (m_canDevice)
              emit canDeviceChanged(1); 
          

          in backend.h

          public slots:
              void statuspican(int value);
          

          in backend.cpp

          void Backend::statuspican(int value)
          {
          qDebug() << "from Mainwindow :" << value;
          }
          
          jsulmJ Offline
          jsulmJ Offline
          jsulm
          Lifetime Qt Champion
          wrote on last edited by
          #7

          @dziko147 said in signal/slot between two different classes:

          connect(this, SIGNAL(canDeviceChanged(int value )),&back, SLOT(statuspican2(int value)));

          Remove "value". Old style connect does only contain the parameter type, not its name.
          But you should really switch to new Qt5 connect syntax - if you then do something wrong you will get a compiler error. With old style connect you only get a runtime warning if connect fails.

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

          1 Reply Last reply
          0
          • D Offline
            D Offline
            dziko147
            wrote on last edited by
            #8

            so logically it should works , there is no syntax error ! ?

            jsulmJ KroMignonK 2 Replies Last reply
            0
            • D dziko147

              so logically it should works , there is no syntax error ! ?

              jsulmJ Offline
              jsulmJ Offline
              jsulm
              Lifetime Qt Champion
              wrote on last edited by
              #9

              @dziko147 Did you read what I and @KroMignon wrote?

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

              1 Reply Last reply
              0
              • D dziko147

                so logically it should works , there is no syntax error ! ?

                KroMignonK Offline
                KroMignonK Offline
                KroMignon
                wrote on last edited by KroMignon
                #10

                @dziko147 said in signal/slot between two different classes:

                so logically it should works , there is no syntax error ! ?

                Are you jocking?

                Nothing is correct:

                • the slot name is wrong
                • the SIGNAL() syntax is wrong ==> only signal signature means: signal name and parameter types
                • the SLOT() syntax is wrong ==> only slot signature means: slot name and parameter types

                It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth. (Sherlock Holmes)

                D 1 Reply Last reply
                3
                • KroMignonK KroMignon

                  @dziko147 said in signal/slot between two different classes:

                  so logically it should works , there is no syntax error ! ?

                  Are you jocking?

                  Nothing is correct:

                  • the slot name is wrong
                  • the SIGNAL() syntax is wrong ==> only signal signature means: signal name and parameter types
                  • the SLOT() syntax is wrong ==> only slot signature means: slot name and parameter types
                  D Offline
                  D Offline
                  dziko147
                  wrote on last edited by
                  #11

                  @KroMignon ok could you provide a connect implementation to solve this .

                  i am blocked since 3 days :/

                  KroMignonK 1 Reply Last reply
                  0
                  • Christian EhrlicherC Offline
                    Christian EhrlicherC Offline
                    Christian Ehrlicher
                    Lifetime Qt Champion
                    wrote on last edited by
                    #12

                    @dziko147 said in signal/slot between two different classes:

                    ok could you provide a connect implementation to solve this .

                    @jsulm already told you what's wrong and you should switch over to the new signal/slot syntax so you get proper compile time errors instead during runtime.

                    Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
                    Visit the Qt Academy at https://academy.qt.io/catalog

                    1 Reply Last reply
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                    • D dziko147

                      @KroMignon ok could you provide a connect implementation to solve this .

                      i am blocked since 3 days :/

                      KroMignonK Offline
                      KroMignonK Offline
                      KroMignon
                      wrote on last edited by
                      #13

                      @dziko147 said in signal/slot between two different classes:

                      ok could you provide a connect implementation to solve this .
                      i am blocked since 3 days :/

                      Can you read?

                      @jsulm told you what to do:

                      Remove "value". Old style connect does only contain the parameter type, not its name.

                      And in Qt documentation:

                      Note that the signal and slots parameters must not contain any variable names, only the type. E.g. the following would not work and return false:

                      // WRONG
                      QObject::connect(scrollBar, SIGNAL(valueChanged(int value)),
                                   label, SLOT(setNum(int value)));
                      
                      // CORRECT
                      QObject::connect(scrollBar, SIGNAL(valueChanged(int)),
                                  label,  SLOT(setNum(int)));
                      

                      I cannot believe this take 3 days to understand.

                      It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth. (Sherlock Holmes)

                      1 Reply Last reply
                      1
                      • D Offline
                        D Offline
                        dziko147
                        wrote on last edited by
                        #14

                        @KroMignon even i remove the "value" it doesn't works .
                        I didn't understand why .
                        No error but the application spits .

                        KroMignonK jsulmJ 2 Replies Last reply
                        0
                        • D dziko147

                          @KroMignon even i remove the "value" it doesn't works .
                          I didn't understand why .
                          No error but the application spits .

                          KroMignonK Offline
                          KroMignonK Offline
                          KroMignon
                          wrote on last edited by
                          #15

                          @dziko147 said in signal/slot between two different classes:

                          No error but the application spits .

                          Why not using the debugger to find out why your application crash?

                          And in you connect:

                          connect(this, SIGNAL(canDeviceChanged(int)),&back, SLOT(statuspican(int)));
                          

                          What is back?
                          Where is it defined?

                          It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth. (Sherlock Holmes)

                          1 Reply Last reply
                          1
                          • D dziko147

                            @KroMignon even i remove the "value" it doesn't works .
                            I didn't understand why .
                            No error but the application spits .

                            jsulmJ Offline
                            jsulmJ Offline
                            jsulm
                            Lifetime Qt Champion
                            wrote on last edited by
                            #16

                            @dziko147 Next thing to check: what does connect() call return?

                            qDebug() << connect(this, SIGNAL(canDeviceChanged(int)),&back, SLOT(statuspican(int)));
                            

                            Next: did you make sure that the signal is actually emitted?

                            if (m_canDevice) {
                                qDebug() << "Emit signal";
                                emit canDeviceChanged(1);
                            }
                            

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

                            D 1 Reply Last reply
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                            • jsulmJ jsulm

                              @dziko147 Next thing to check: what does connect() call return?

                              qDebug() << connect(this, SIGNAL(canDeviceChanged(int)),&back, SLOT(statuspican(int)));
                              

                              Next: did you make sure that the signal is actually emitted?

                              if (m_canDevice) {
                                  qDebug() << "Emit signal";
                                  emit canDeviceChanged(1);
                              }
                              
                              D Offline
                              D Offline
                              dziko147
                              wrote on last edited by
                              #17

                              @jsulm

                              qDebug() << connect(this, SIGNAL(canDeviceChanged(int)),&back, SLOT(statuspican(int)));
                              

                              return true .

                              And the signal is emmited

                              SGaistS 1 Reply Last reply
                              0
                              • D dziko147

                                @jsulm

                                qDebug() << connect(this, SIGNAL(canDeviceChanged(int)),&back, SLOT(statuspican(int)));
                                

                                return true .

                                And the signal is emmited

                                SGaistS Offline
                                SGaistS Offline
                                SGaist
                                Lifetime Qt Champion
                                wrote on last edited by
                                #18

                                Hi,

                                @dziko147 said in signal/slot between two different classes:

                                @jsulm

                                qDebug() << connect(this, SIGNAL(canDeviceChanged(int)),&back, SLOT(statuspican(int)));
                                

                                return true .

                                And the signal is emmited

                                Where is back defined ?
                                Any chances that this is a function local variable that is destroyed at the end of it ?

                                Interested in AI ? www.idiap.ch
                                Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                                D 1 Reply Last reply
                                0
                                • SGaistS SGaist

                                  Hi,

                                  @dziko147 said in signal/slot between two different classes:

                                  @jsulm

                                  qDebug() << connect(this, SIGNAL(canDeviceChanged(int)),&back, SLOT(statuspican(int)));
                                  

                                  return true .

                                  And the signal is emmited

                                  Where is back defined ?
                                  Any chances that this is a function local variable that is destroyed at the end of it ?

                                  D Offline
                                  D Offline
                                  dziko147
                                  wrote on last edited by
                                  #19

                                  @SGaist

                                  Backend is my second class . the class which i want to get data in .
                                  So back is an instance of Backend .

                                  So i defined like this :

                                  Backend back; 
                                  
                                  1 Reply Last reply
                                  0
                                  • SGaistS Offline
                                    SGaistS Offline
                                    SGaist
                                    Lifetime Qt Champion
                                    wrote on last edited by
                                    #20

                                    The question is: where is it defined ?

                                    Interested in AI ? www.idiap.ch
                                    Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                                    1 Reply Last reply
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                                    • D Offline
                                      D Offline
                                      dziko147
                                      wrote on last edited by
                                      #21

                                      @SGaist

                                      MainWindow::MainWindow(QWidget *parent) :
                                          QMainWindow(parent),
                                          m_ui(new Ui::MainWindow),
                                      {
                                          m_ui->setupUi(this);
                                          
                                          Backend back ;
                                      connect(this, SIGNAL(canDeviceChanged(int)),&back, SLOT(statuspican(int)));
                                      
                                      KroMignonK 1 Reply Last reply
                                      0
                                      • SGaistS Offline
                                        SGaistS Offline
                                        SGaist
                                        Lifetime Qt Champion
                                        wrote on last edited by
                                        #22

                                        That's what I suspected: back is destroyed at the end of the constructor.

                                        Interested in AI ? www.idiap.ch
                                        Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                                        1 Reply Last reply
                                        3
                                        • D dziko147

                                          @SGaist

                                          MainWindow::MainWindow(QWidget *parent) :
                                              QMainWindow(parent),
                                              m_ui(new Ui::MainWindow),
                                          {
                                              m_ui->setupUi(this);
                                              
                                              Backend back ;
                                          connect(this, SIGNAL(canDeviceChanged(int)),&back, SLOT(statuspican(int)));
                                          
                                          KroMignonK Offline
                                          KroMignonK Offline
                                          KroMignon
                                          wrote on last edited by KroMignon
                                          #23

                                          @dziko147 said in signal/slot between two different classes:

                                          {

                                          m_ui->setupUi(this);
                                          Backend back ;
                                          connect(this, SIGNAL(canDeviceChanged(int)),&back, SLOT(statuspican(int)));
                                          

                                          I know that you are a C++/Qt beginner, but as many times written: please take time to understand C++ basics.

                                          C++ variable scope and life-cycle is one of them:

                                          • https://www.tutorialspoint.com/cplusplus/cpp_variable_scope.htm
                                          • https://www.geeksforgeeks.org/scope-of-variables-in-c/
                                          • there are many more available on internet

                                          If you don't learn, how do you expect programming?

                                          It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth. (Sherlock Holmes)

                                          1 Reply Last reply
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