Qt Signal Connect Problem

[Jay3205]

I'm a relatively new programmer, and I'm trying to make a program to play a collectible card game online using Qt and QDevelop IDE. However, I'm currently running into a problem trying to connect a signal from my main window class to a player class slot. It compiles fine, but it crashes the program when the program is run. Here's the code:

MAIN WINDOW header ifle

#ifndef MAINWINDOWIMPL_H
#define MAINWINDOWIMPL_H

#include <QMainWindow>
#include "ui_mainwindow.h"
#include "card.h"
#include "definitions.h"
#include "player.h"
#include "bigPic.h"

class MainWindowImpl : public QMainWindow, public Ui::MainWindow
{
Q_OBJECT
public:
MainWindowImpl( QWidget * parent = 0, Qt::WFlags f = 0 );

// the various parts of the form
QGraphicsScene playerFieldScene;
QGraphicsScene opponentFieldScene;
QGraphicsScene bigPicScene;
QGraphicsScene handScene;
BigPic bigPic;

Player * player;
Player * opponent;

private:
void startup();
void initializeBigPic();

signals:
void loadPlayerDeck(QString filename);

public slots:
void resetPlayers();

};
#endif

MAIN WINDOW cpp

#include "mainwindowimpl.h"
#include <QtGui>

MainWindowImpl::MainWindowImpl( QWidget * parent, Qt::WFlags f)
: QMainWindow(parent, f)
{
// load the user interface
setupUi(this);

startup();

// load the player's deck
emit loadPlayerDeck("");

// initialize the big pic
initializeBigPic();

}

// attach scenes to views and handle all signal/slot connections
void MainWindowImpl::startup()
{
// attach scenes to views
playerFieldView->setScene(&playerFieldScene);
opponentFieldView->setScene(&opponentFieldScene);
bigPicView->setScene(&bigPicScene);
handView->setScene(&handScene);

// signal and slot connections **** FOLLOWING LINE CAUSES RUNTIME PROBLEM ******
connect(this, SIGNAL(loadPlayerDeck(QString)), player, SIGNAL(loadDeck(QString)));

}

/* initialize the scene containing the big picture of a card */
void MainWindowImpl::initializeBigPic()
{
// render the big picture
bigPicScene.addItem(&bigPic);

//bigPic.setTransform(QTransform().rotate(60, Qt::YAxis));
}

// reset the deck, field, grave, hand, and mana zone of each player
void MainWindowImpl::resetPlayers(){
player->resetZones();
opponent->resetZones();

}

PLAYER header file

#ifndef __PLAYER_H__
#define __PLAYER_H__

#include <QObject>
#include "card.h"
#include "definitions.h"

class Player : public QObject
{
Q_OBJECT

public:
Player();

QString name;
QList<Card *> deck; // position 0 is the top of the deck
QList<Card *> field;
QList<Card *> mana;
QList<Card *> grave;
QList<Card *> hand;

void setDeck(QList<Card *> newDeck);
void resetZones();

signals:

public slots:
void loadDeck(QString filename);

};

#endif

When I run this, it crashes with the following message:

Program received signal SIGSEGV, Segmentation fault.
0xb7223d8b in QObject::connect (sender=0xbfee6e90, signal=0x80509f8 "loadPlayerDeck(QString)", receiver=0x804b728, method=0x80509e5 "loadDeck(QString)", type=Qt::AutoConnection) at kernel/qobject.cpp:2403

Any help would be greatly appreciated.

[scourge]

You're telling the connect function that Player::loadDeck is a signal, when it's actually a slot.

Change this:

connect(this, SIGNAL(loadPlayerDeck(QString)), player, SIGNAL(loadDeck(QString)));
to this:

connect(this, SIGNAL(loadPlayerDeck(QString)), player, SLOT(loadDeck(QString)));

Btw, instead of passing containers like QList and QString by value, you should pass them by const reference.

[Jay3205]

I've made the change, but it is still the same error. I've tried connecting them as a signal and a slot, and I've changed loadDeck into a signal and tried connecting them, but it gives the same error. However, when I make the following change, the program works:

replace:

// signal and slot connections
connect(this, SIGNAL(loadPlayerDeck(QString)), player, SIGNAL(loadDeck(QString)));

with

// signal and slot connections
Player * p;
connect(this, SIGNAL(loadPlayerDeck(QString)), p, SIGNAL(loadDeck(QString)));

Of course, doing this doesn't really solve the problem, and I have no idea why that even works. Any more recommendations?

[scourge]

Looks like you're not initializing the player. You should have "player = new Player;" in MainWindowImpl's constructor (and delete it in the destructor).

[Jay3205]

Thanks! Not intializing it was the problem.