[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.