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signal/slot between two different classes

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  • 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.

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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)

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        • 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; 
                    
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                    • 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

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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

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                          • 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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                            • D Offline
                              D Offline
                              dziko147
                              wrote on last edited by
                              #24

                              @KroMignon Hello
                              to create a global variable . Can i create Backend back; in MainWindow.h .

                              KroMignonK 1 Reply Last reply
                              0
                              • D dziko147

                                @KroMignon Hello
                                to create a global variable . Can i create Backend back; in MainWindow.h .

                                KroMignonK Offline
                                KroMignonK Offline
                                KroMignon
                                wrote on last edited by
                                #25

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

                                to create a global variable . Can i create Backend back; in MainWindow.h .

                                I don't want to be pedantic, but as you seems to be very unexperimented I will try to be as clear as possible.

                                There is no need of a global variable at all.

                                For me, there are 2 clean way to do it:

                                1. create a variable in main() and do all connection there.
                                2. add a class attribute from type Backend into MainWindow and eventually give access to it through getter.

                                My preferred way is the second.
                                But this is up to you.

                                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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