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signal/slot between two different classes

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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
        0
        • 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
                0
                • 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
                      3
                      • 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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