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Passing another variable to a SLOT in QObject::connect

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  • M Offline
    M Offline
    manasij7479
    wrote on last edited by
    #3

    bq. simply use a “proxy” slot that calls the target slot with the arguments....

    How do I do that?

    "Error, no keyboard — press F1 to continue."

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    • F Offline
      F Offline
      Franzk
      wrote on last edited by
      #4

      @
      //...
      connect(button, SIGNAL(pressed)), SLOT(handleButtonPress()));
      //...

      void MyClass::handleButtonPress()
      {
      someLabel->setText("My String");
      }@

      "Horse sense is the thing a horse has which keeps it from betting on people." -- W.C. Fields

      http://www.catb.org/~esr/faqs/smart-questions.html

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      • D Offline
        D Offline
        dangelog
        wrote on last edited by
        #5

        In your (very simple) case, if it's applicable, you can just provide a default argument for the slot. Otherwise, simply create another slot that calls the setText one with the string you want.

        Software Engineer
        KDAB (UK) Ltd., a KDAB Group company

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        • F Offline
          F Offline
          Franzk
          wrote on last edited by
          #6

          [quote author="peppe" date="1297240228"]In your (very simple) case, if it's applicable, you can just provide a default argument for the slot. Otherwise, simply create another slot that calls the setText one with the string you want.[/quote]Indeed. With a slot called setText(), providing a default argument can be misleading:

          @myLabel->setText();@

          What does that do?

          Oh well. It's a style issue.

          "Horse sense is the thing a horse has which keeps it from betting on people." -- W.C. Fields

          http://www.catb.org/~esr/faqs/smart-questions.html

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          • M Offline
            M Offline
            manasij7479
            wrote on last edited by
            #7

            bq. Otherwise, simply create another slot that calls the setText one with the string you want.

            Any way without creating whole new classes?

            "Error, no keyboard — press F1 to continue."

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            • T Offline
              T Offline
              tobias.hunger
              wrote on last edited by
              #8

              "QSignalMapper":http://doc.qt.nokia.com/4.7/qsignalmapper.html might also be an option.

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              • L Offline
                L Offline
                luca
                wrote on last edited by
                #9

                to solve simple problem like yours I use this solution:
                @
                connect(button1, SIGNAL(clicked()), SLOT(buttonClicked());
                connect(button2, SIGNAL(clicked()), SLOT(buttonClicked());
                button1->setProperty("name", "button1");
                button2->setProperty("name", "button2");
                ...
                ...
                MyClass::buttonClicked()
                {
                QPushButton *button = sender();
                if(button->property("name").toString() == "button1")
                {
                .....
                .....
                }
                else if(button->property("name").toString() == "button2")
                {
                ....
                ....
                }
                }
                @

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                • A Offline
                  A Offline
                  andre
                  wrote on last edited by
                  #10

                  Luca, that is unsave code.

                  You don't know what kind of object sender() refers to, or if it is non-0 at all (direct call to buttonClicked()). So, you should at least check that before assuming this. Using a QSignalMapper is the safe way to go, and it still allows other ways to trigger the slot and still work correctly.

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                  • F Offline
                    F Offline
                    Franzk
                    wrote on last edited by
                    #11

                    Safe or not safe, it's arguably not even simpler than the QSignalMapper approach. Likewise, if a slot is going to make (significant) behavioral changes based on the sender(), then it is probably time to review the design anyway.

                    "Horse sense is the thing a horse has which keeps it from betting on people." -- W.C. Fields

                    http://www.catb.org/~esr/faqs/smart-questions.html

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                    • L Offline
                      L Offline
                      luca
                      wrote on last edited by
                      #12

                      [quote author="Andre" date="1297288071"]Luca, that is unsave code.

                      You don't know what kind of object sender() refers to, or if it is non-0 at all (direct call to buttonClicked()). So, you should at least check that before assuming this. Using a QSignalMapper is the safe way to go, and it still allows other ways to trigger the slot and still work correctly.
                      [/quote]
                      Yes, I usually check if pointer is a push button with a dynamic_cast:
                      @
                      QPushButton button = dynamic_cast<QPushButton>(sender());
                      if(button==NULL)
                      {
                      return;
                      }
                      @

                      Mine is only a fast example...

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                      • F Offline
                        F Offline
                        Franzk
                        wrote on last edited by
                        #13

                        qobject_cast might be more thorough.

                        "Horse sense is the thing a horse has which keeps it from betting on people." -- W.C. Fields

                        http://www.catb.org/~esr/faqs/smart-questions.html

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                        • M Offline
                          M Offline
                          MarekR22
                          wrote on last edited by
                          #14

                          Hi there is a tool which do exactly what you need.
                          See "QSignalMapper":http://doc.trolltech.com/latest/qsignalmapper.html
                          There is good example how to use it.

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                          • G Offline
                            G Offline
                            goetz
                            wrote on last edited by
                            #15

                            If you're in the same class (or have access to the possible sender objects pointers) you simply can compare pointers:

                            @
                            void MyClass::buttonClicked()
                            {
                            if(sender() == button1) {
                            // ....
                            } else if(sender() == button2) {
                            // ....
                            }
                            }
                            @

                            http://www.catb.org/~esr/faqs/smart-questions.html

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