[SOLVED] Calling a function from another class

[Demmy]

I understand this is an extremely beginner's question and more related to c++ itself than it is to qt but sadly I cannot seem to understand where the problem is at this point.

Intention: I wish to call a function which is located in glavni.cpp and set under public in glavni.h, from nasascena.cpp when a mouse event is triggered.

Current situation: I got the mousepressevent itself to work, so the only thing left is calling a function.

glavni.cpp
@
//bunch of stuff
void glavni::elipsaOFF()
{
ui->label->setText("YOU PRESSED IT");
}
@

glavni.h
@class glavni : public QMainWindow
{
Q_OBJECT

public:
explicit glavni(QWidget *parent = 0);
~glavni();

void elipsaOFF();

//other stuff@

nasascena.cpp
@#include "nasascena.h"
#include "glavni.h"

#include <QGraphicsSceneMouseEvent>
nasaScena::nasaScena()
{
}

void nasaScena::mousePressEvent(QGraphicsSceneMouseEvent *event)
{
glavni g;
g.elipsaOFF();
//other working stuff @

What happens: It runs, no errors. When I get to the mouse event, everything under it executes except the g.elipsaOFF(); part
I tried going glavni::elipsaOFF(); with the static void, but it didn't work as intended. Any tips?

[t3685]

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

[p3c0]

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.

[Demmy]

@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.

[p3c0]

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

[Demmy]

[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.

[p3c0]

bq. change the existing one.

Do you mean you want to add this widget ?

[Demmy]

[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.

[p3c0]

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.

[Demmy]

[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.

[p3c0]

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)

[Demmy]

[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.

[p3c0]

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

[Demmy]

[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.

[p3c0]

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.

[Demmy]

[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

[Demmy]

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.

[t3685]

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

[Demmy]

[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.

[t3685]

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