Slot doesn't work in new window

[mohjlir]

I create a main window, which opens a new window on a button click. That works fine, but the new window's button doesn't respond to clicks. I have included Q_OBJECT in the class declaration. The code is as follows:

main.cpp:

#include <QtGui/QApplication>
#include "mainwindow.h"
#include "AnotherWindow.h"
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
 
    return a.exec();
}

#include <QtGui/QApplication>
#include "mainwindow.h"
#include "AnotherWindow.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    return a.exec();
}

To copy to clipboard, switch view to plain text mode 

mainwindow.h:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
 
#include <QObject>
#include <QWidget>
 
class MainWindow : public QWidget
{
    Q_OBJECT
 
public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();
private slots:
    void TestFunction();
};
 
#endif // MAINWINDOW_H

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QObject>
#include <QWidget>

class MainWindow : public QWidget
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();
private slots:
    void TestFunction();
};

#endif // MAINWINDOW_H

To copy to clipboard, switch view to plain text mode 

mainwindow.cpp:

#include <QtGui>
#include "mainwindow.h"
#include "AnotherWindow.h"
 
MainWindow::MainWindow(QWidget *parent)
: QWidget(parent)
{
    QPushButton* pb = new QPushButton("Test");
    QVBoxLayout* layout = new QVBoxLayout;
    layout->addWidget(pb);
    this->setLayout(layout);
    connect(pb, SIGNAL( clicked() ), this, SLOT( TestFunction() ));
}
 
void MainWindow::TestFunction()
{
    qDebug("This is a test");
    AnotherWindow aw;
}
 
MainWindow::~MainWindow()
{
}

#include <QtGui>
#include "mainwindow.h"
#include "AnotherWindow.h"

MainWindow::MainWindow(QWidget *parent)
: QWidget(parent)
{
    QPushButton* pb = new QPushButton("Test");
    QVBoxLayout* layout = new QVBoxLayout;
    layout->addWidget(pb);
    this->setLayout(layout);
    connect(pb, SIGNAL( clicked() ), this, SLOT( TestFunction() ));
}

void MainWindow::TestFunction()
{
    qDebug("This is a test");
    AnotherWindow aw;
}

MainWindow::~MainWindow()
{
}

To copy to clipboard, switch view to plain text mode 

AnotherWindow.h:

#ifndef ANOTHERWINDOW_H
#define ANOTHERWINDOW_H
 
#include <QObject>
#include <QWidget>
 
class AnotherWindow : public QWidget
{
 
    Q_OBJECT
 
public:
    AnotherWindow(QWidget* parent = 0);
private slots:
    void AnotherTest();
}
;
 
#endif // ANOTHERWINDOW_H

#ifndef ANOTHERWINDOW_H
#define ANOTHERWINDOW_H

#include <QObject>
#include <QWidget>

class AnotherWindow : public QWidget
{

    Q_OBJECT

public:
    AnotherWindow(QWidget* parent = 0);
private slots:
    void AnotherTest();
}
;

#endif // ANOTHERWINDOW_H

To copy to clipboard, switch view to plain text mode 

AnotherWindow.cpp:

#include <QtGui>
#include <QDebug>
#include "AnotherWindow.h"
 
AnotherWindow::AnotherWindow(QWidget* parent)
{
    QWidget* window = new QWidget;
    QVBoxLayout* anotherLayout = new QVBoxLayout;
    QPushButton* pushy = new QPushButton("OMGWTFBBQ");
    anotherLayout->addWidget(pushy);
    connect(pushy, SIGNAL(clicked()), this, SLOT(AnotherTest()));
    window->setLayout(anotherLayout);
    window->show();
}
 
void AnotherWindow::AnotherTest()
{
   qDebug("Why isn't this code hit?");
}

#include <QtGui>
#include <QDebug>
#include "AnotherWindow.h"

AnotherWindow::AnotherWindow(QWidget* parent)
{
    QWidget* window = new QWidget;
    QVBoxLayout* anotherLayout = new QVBoxLayout;
    QPushButton* pushy = new QPushButton("OMGWTFBBQ");
    anotherLayout->addWidget(pushy);
    connect(pushy, SIGNAL(clicked()), this, SLOT(AnotherTest()));
    window->setLayout(anotherLayout);
    window->show();
}

void AnotherWindow::AnotherTest()
{
   qDebug("Why isn't this code hit?");
}

To copy to clipboard, switch view to plain text mode 

[franz]

Here's one (and possibly the) problem:

void MainWindow::TestFunction()
{
    qDebug("This is a test");
    AnotherWindow aw;
}

void MainWindow::TestFunction()
{
    qDebug("This is a test");
    AnotherWindow aw;
}

To copy to clipboard, switch view to plain text mode 

Here you instantiate an AnotherWindow on the stack. What happens here is that the window you create gets destroyed immediately after construction. The push button's clicked() signal automagically detects that the connection was broken, hence there is no activity. The widget you see is the widget created in the AnotherWindow constructor (which is superfluous, btw).

Better code would probably be:

void MainWindow::TestFunction()
{
    qDebug("This is a test");
    AnotherWindow *aw = new AnotherWindow(this);
    aw->show();
}

void MainWindow::TestFunction()
{
    qDebug("This is a test");
    AnotherWindow *aw = new AnotherWindow(this);
    aw->show();
}

To copy to clipboard, switch view to plain text mode 

AnotherWindow::AnotherWindow(QWidget* parent)
{
    QVBoxLayout* anotherLayout = new QVBoxLayout;
    QPushButton* pushy = new QPushButton("OMGWTFBBQ");
    anotherLayout->addWidget(pushy);
    connect(pushy, SIGNAL(clicked()), this, SLOT(AnotherTest()));
    setLayout(anotherLayout);
}

AnotherWindow::AnotherWindow(QWidget* parent)
{
    QVBoxLayout* anotherLayout = new QVBoxLayout;
    QPushButton* pushy = new QPushButton("OMGWTFBBQ");
    anotherLayout->addWidget(pushy);
    connect(pushy, SIGNAL(clicked()), this, SLOT(AnotherTest()));
    setLayout(anotherLayout);
}

To copy to clipboard, switch view to plain text mode 

Hope this helps.

On an unrelated note, you don't need to explicitly include QObject before you include QWidget. QWidget is a QObject and the dependency implications are handled for you by the compiler. It won't make much of a difference during compiling, it is more of a style issue.

[mohjlir]

Perfect, thanks for your help!