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[SOLVED] Calling a function from another class

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  • T Offline
    T Offline
    t3685
    wrote on last edited by
    #2

    What do you mean nothing happens? I suspect the text of your label isn't changing?

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    0
    • p3c0P Offline
      p3c0P Offline
      p3c0
      Moderators
      wrote on last edited by
      #3

      Hi,

      The glavni class object is destroyed as soon as the function exits and hence nothing is displayed.
      You should rather create the object on heap.

      157

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      • D Offline
        D Offline
        Demmy
        wrote on last edited by
        #4

        @t3685

        Yes, the label does not change. I previously put in some other functions from the same class to call and they do not execute. If I put in a variable, it does not change. It is as if the function does not trigger at all.

        @p3c0

        Can you suggest how it should look? Would be much appriciated.

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        • p3c0P Offline
          p3c0P Offline
          p3c0
          Moderators
          wrote on last edited by
          #5

          Just use the new keyword.
          So,
          @
          glavni *g = new glavni;
          g->show();
          g->elipsaOFF();
          @

          157

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          • D Offline
            D Offline
            Demmy
            wrote on last edited by
            #6

            [quote author="p3c0" date="1403359381"]Just use the new keyword.
            So,
            @
            glavni *g = new glavni;
            g->show();
            g->elipsaOFF();
            @[/quote]

            ok, this works but it creates a completely new window. I would like to change the existing one.

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            • p3c0P Offline
              p3c0P Offline
              p3c0
              Moderators
              wrote on last edited by
              #7

              bq. change the existing one.

              Do you mean you want to add this widget ?

              157

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              • D Offline
                D Offline
                Demmy
                wrote on last edited by
                #8

                [quote author="p3c0" date="1403361027"]bq. change the existing one.

                Do you mean you want to add this widget ?[/quote]

                Yes - add to the existing widget, glavni.cpp is a widget with a graphicsview and some other stuff in it and nasascena.cpp is basically qgraphicsscene which is imported in on the view in glavni.cpp. I want to be able to change things on the existing widget of glavni.cpp when I click inside the scene, changing the label name (using elipsaOFF()) was just a way for me to check on how it all works.

                I have to figure it out somehow :)

                For a future reference and why I'm asking for this:
                I would like to get coordinates on a mouse click on the scene (already done below in the nasascena.cpp). They already are an extern float, but I would like to trigger a function inside glavni.cpp which would for example draw a line with coordinates provided.
                I thought calling a function would be way simpler to do though.

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                • p3c0P Offline
                  p3c0P Offline
                  p3c0
                  Moderators
                  wrote on last edited by
                  #9

                  So basically you can use "setScene":http://qt-project.org/doc/qt-4.8/qgraphicsview.html#setScene function to set the QGraphicsScene to a QGraphicsView.
                  So in general for eg.
                  @
                  QGraphicsScene *m_scene = new QGraphicsScene(this);
                  ui->graphicsView->setScene(m_scene);
                  @

                  Adjust the QGraphicView and QGraphicsScene Objects as per your need.

                  157

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                  • D Offline
                    D Offline
                    Demmy
                    wrote on last edited by
                    #10

                    [quote author="p3c0" date="1403362183"]So basically you can use "setScene":http://qt-project.org/doc/qt-4.8/qgraphicsview.html#setScene function to set the QGraphicsScene to a QGraphicsView.
                    So in general for eg.
                    @
                    QGraphicsScene *m_scene = new QGraphicsScene(this);
                    ui->graphicsView->setScene(m_scene);
                    @

                    Adjust the QGraphicView and QGraphicsScene Objects as per your need.[/quote]
                    it is already done:
                    glavni.cpp
                    @
                    #include "glavni.h"
                    #include "ui_glavni.h"
                    #include "nasascena.h"
                    #include "nasaelipsa.h"

                    #include<QGraphicsScene>
                    glavni::glavni(QWidget *parent) :
                    QMainWindow(parent),
                    ui(new Ui::glavni)
                    {
                    ui->setupUi(this);

                    scene= new nasaScena();
                    ui->graphicsView->setScene(scene);
                    elipsa[0] = new nasaElipsa(); //irrelevant in this case
                    scene->addItem(elipsa[0]); //irrelevant in this case
                    

                    }

                    glavni::~glavni()
                    {
                    delete ui;
                    }

                    void glavni::elipsaOFF()
                    {
                    //Pritisnuto=true;
                    //elipsaToggle();
                    ui->label->setText("YOU PRESSED IT");
                    //elipsaON();
                    }
                    @
                    at this point it is very important to me to somehow trigger this function though, scene and view work fine.

                    Pic:

                    http://i58.tinypic.com/33e6duh.jpg

                    but it is all irrelevant at this point, all I want to do is to execute elipsaOFF() in glavni.cpp from nasascena.cpp without creating a completely new window.

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                    • p3c0P Offline
                      p3c0P Offline
                      p3c0
                      Moderators
                      wrote on last edited by
                      #11

                      Ok. So better would be to use the "Signals and Slots":http://qt-project.org/doc/qt-4.8/signalsandslots.html mechanism.
                      Emit a custom signal say for eg. onSceneClicked() from mousePressEvent() function of nasaScena class.
                      And connect this signal to elipsaOFF() (you need to declare this as a slot)

                      157

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                      • D Offline
                        D Offline
                        Demmy
                        wrote on last edited by
                        #12

                        [quote author="p3c0" date="1403363202"]Ok. So better would be to use the "Signals and Slots":http://qt-project.org/doc/qt-4.8/signalsandslots.html mechanism.
                        Emit a custom signal say for eg. onSceneClicked() from mousePressEvent() function of nasaScena class.
                        And connect this signal to elipsaOFF() (you need to declare this as a slot)[/quote]

                        Interesting approach, will try. I thought something like calling a function would be the most basic way to perform it.

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                        • p3c0P Offline
                          p3c0P Offline
                          p3c0
                          Moderators
                          wrote on last edited by
                          #13

                          Signals and Slots is the most recommended and an important aspect of Qt programming.

                          157

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                          • D Offline
                            D Offline
                            Demmy
                            wrote on last edited by
                            #14

                            [quote author="p3c0" date="1403363782"]Signals and Slots is the most recommended and an important aspect of Qt programming.[/quote]

                            Ok, I tried this (correct plz if I misunderstood)
                            @#include "nasascena.h"
                            #include "glavni.h"

                            #include <QGraphicsSceneMouseEvent>

                            nasaScena::nasaScena()
                            {
                            connect(mousePressEvent, SIGNAL(event), glavni, SLOT(glavni::elipsaOFF()));
                            }

                            void nasaScena::mousePressEvent(QGraphicsSceneMouseEvent *event)
                            {
                            //glavni g;
                            //g.elipsaOFF();
                            update();
                            QGraphicsScene::mousePressEvent(event);
                            }@

                            This does not work; returns "expected primary-expression before ',' token...

                            points at "glavni," at the end of it in connect.

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                            • p3c0P Offline
                              p3c0P Offline
                              p3c0
                              Moderators
                              wrote on last edited by
                              #15

                              That won't work since event is not a signal and the Connect's syntax is wrong.

                              First you must declare a new signal in nasaScena.h

                              nasaScena.h
                              @
                              signals:
                              void onSceneClicked();
                              @

                              Emit this signal in mousePressEvent
                              @
                              void nasaScena::mousePressEvent(QGraphicsSceneMouseEvent *event)
                              {
                              emit onSceneClicked();
                              }
                              @

                              Then in Main class glavni declare elipsaOFF() as a slot.

                              glavni.h
                              @
                              protected slots:
                              void elipsaOFF();
                              @

                              and then in glavni.cpp connect the signal onSceneClicked() to the newly created slot. So

                              glavni.cpp
                              @
                              ui->setupUi(this);
                              scene= new nasaScena();
                              connect(scene,SIGNAL(onSceneClicked()),this,SLOT(elipsaOFF()));
                              @

                              Thus the signal should trigger the slot.

                              157

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                              • D Offline
                                D Offline
                                Demmy
                                wrote on last edited by
                                #16

                                [quote author="p3c0" date="1403365994"]That won't work since event is not a signal and the Connect's syntax is wrong.

                                First you must declare a new signal in nasaScena.h

                                nasaScena.h
                                @
                                signals:
                                void onSceneClicked();
                                @

                                Emit this signal in mousePressEvent
                                @
                                void nasaScena::mousePressEvent(QGraphicsSceneMouseEvent *event)
                                {
                                emit onSceneClicked();
                                }
                                @

                                Then in Main class glavni declare elipsaOFF() as a slot.

                                glavni.h
                                @
                                protected slots:
                                void elipsaOFF();
                                @

                                and then in glavni.cpp connect the signal onSceneClicked() to the newly created slot. So

                                glavni.cpp
                                @
                                ui->setupUi(this);
                                scene= new nasaScena();
                                connect(scene,SIGNAL(onSceneClicked()),this,SLOT(elipsaOFF()));
                                @

                                Thus the signal should trigger the slot.[/quote]

                                Did all that, now it says: "undefined reference to 'nasaScena::onSceneClicked()'
                                this is on the @emit onSceneClicked();@ line. Googled for it, no luck. Why this won't work is beyond me. I declared the signal the way you said:

                                in nasascena.h
                                @signals:
                                void onSceneClicked();@

                                and it gives me shit when I try to emit it from nasascena.cpp

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                                • D Offline
                                  D Offline
                                  Demmy
                                  wrote on last edited by
                                  #17

                                  Ok, apparently I had to add Q_OBJECT macro in nasascena.h and run qmake for it to work. Although I'd still like to know how to run a function from the outside I declare this problem solved. Many thanks to p3c0 for bearing with me.

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                                  • T Offline
                                    T Offline
                                    t3685
                                    wrote on last edited by
                                    #18

                                    Hi Demmy,

                                    What you seem to confused about is the following:

                                    • you have to call functions on instances of a class, in your case glavni

                                    • what you are doing is making a glavni instance g, and calling your function on that object

                                    • you need to which object you want to call your function on

                                    • best to get reading on C++ or object oriented programming in general

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                                    • D Offline
                                      D Offline
                                      Demmy
                                      wrote on last edited by
                                      #19

                                      [quote author="t3685" date="1403428669"]Hi Demmy,

                                      What you seem to confused about is the following:

                                      • you have to call functions on instances of a class, in your case glavni

                                      • what you are doing is making a glavni instance g, and calling your function on that object

                                      • you need to which object you want to call your function on

                                      • best to get reading on C++ or object oriented programming in general[/quote]
                                        I thought it was something like that after p3c0 gave me an example with new glavni; but sadly I still don't understand how to call on existing object or how is it in this case even defined (can't call on "this" from other cpp file :D ). I guess I could use some serious reading.

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                                      • T Offline
                                        T Offline
                                        t3685
                                        wrote on last edited by
                                        #20

                                        Yes, reading up a bit would do you good :). It's not difficult but you need to know some basic things.

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