Creating a Dialog in a Slot of QMainWindow

[tilm]

Hello,

I created a MainWindow and a very simple Dialog using the Qt Designer. I want to use both components with a single inheritance approach. In a Slot of the MainWindow (connected to an Action of the MainWindow) I want to create and execute an instance of the Dialog class. But when I try to compile the programm there is the error:

release\MainWindow.o(.text+0x28f):MainWindow.cpp: undefined reference to 'Dialog::Dialog(QWidget*)'

I think the proplem might be connected with the fact that I want to create the Dialog in a class derived from QMainWindow. In my project I previously created the Dialog in a Slot of a QAbstractTableModel and it worked fine. Than I decided that this class wasn't the right place to do this and wanted to create the Dialog in a slot of the MainWindow instead ending up with this error.

Here are the files of a minimal example:

MainWindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
 
#include <QMainWindow>
#include "ui_MainWindow.h"
 
class MainWindow : public QMainWindow {
	Q_OBJECT
 
public:	
	MainWindow(QWidget *parent=0,Qt::WFlags flags=0);
 
public slots:
	void createDialog();
 
private:
	Ui::MainWindow *ui;
};
 
#endif

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include "ui_MainWindow.h"

class MainWindow : public QMainWindow {
	Q_OBJECT
	
public:	
	MainWindow(QWidget *parent=0,Qt::WFlags flags=0);
	
public slots:
	void createDialog();
	
private:
	Ui::MainWindow *ui;
};

#endif

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MainWindow.cpp

#include "MainWindow.h"
#include "Dialog.h"
 
MainWindow::MainWindow(QWidget *parent,Qt::WFlags flags){
	ui = new Ui::MainWindow;
	ui->setupUi(this);
 
	connect(ui->actionCreate,SIGNAL(activated()),this,SLOT(createDialog()));
}
 
void MainWindow::createDialog(){
	Dialog *d = new Dialog;
	d->exec();
}

#include "MainWindow.h"
#include "Dialog.h"

MainWindow::MainWindow(QWidget *parent,Qt::WFlags flags){
	ui = new Ui::MainWindow;
	ui->setupUi(this);
	
	connect(ui->actionCreate,SIGNAL(activated()),this,SLOT(createDialog()));
}

void MainWindow::createDialog(){
	Dialog *d = new Dialog;
	d->exec();
}

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Dialog.h

#ifndef MYDIALOG_H
#define MYDIALOG_H
 
#include <QDialog>
#include "ui_Dialog.h"
 
class Dialog : public QDialog {
public:
	Dialog(QWidget *parent = 0);
 
};
 
#endif

#ifndef MYDIALOG_H
#define MYDIALOG_H

#include <QDialog>
#include "ui_Dialog.h"

class Dialog : public QDialog {
public:
	Dialog(QWidget *parent = 0);
	
};

#endif

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Dialog.cpp

#include "Dialog.h"
 
Dialog::Dialog(QWidget *parent = 0) : QWidget(parent){
	Ui::Dialog *ui = new Ui::Dialog;
	ui.setupUi(this);
}

#include "Dialog.h"

Dialog::Dialog(QWidget *parent = 0) : QWidget(parent){
	Ui::Dialog *ui = new Ui::Dialog;
	ui.setupUi(this);
}

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[spirit]

there is trouble

Dialog::Dialog(QWidget *parent = 0)

Dialog::Dialog(QWidget *parent = 0)

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should be

Dialog::Dialog(QWidget *parent )

Dialog::Dialog(QWidget *parent )

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[spirit]

one more, in this method

void MainWindow::createDialog(){
    Dialog *d = new Dialog;
    d->exec();
}

void MainWindow::createDialog(){
    Dialog *d = new Dialog;
    d->exec();
}

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you should set parent or delete dialog manually.

[tilm]

Thanks for your answers but the mistakes you pointed out do not seem to be the crucial ones. I still get the same compiler error. And obviously the compiler stops even before it recognizes the second specification of a default argument in the Dialog constructor because I did not get an error for this.

The second mistake would 'only' cause a memory leak and no compiler error, right?

[spirit]

your code

#include "Dialog.h"
 
Dialog::Dialog(QWidget *parent = 0) : QWidget(parent){
    Ui::Dialog *ui = new Ui::Dialog;
    ui.setupUi(this);
}

#include "Dialog.h"
 
Dialog::Dialog(QWidget *parent = 0) : QWidget(parent){
    Ui::Dialog *ui = new Ui::Dialog;
    ui.setupUi(this);
}

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must be

#include "Dialog.h"
 
Dialog::Dialog(QWidget *parent) : QWidget(parent){
    Ui::Dialog *ui = new Ui::Dialog;
    ui.setupUi(this);
}

#include "Dialog.h"
 
Dialog::Dialog(QWidget *parent) : QWidget(parent){
    Ui::Dialog *ui = new Ui::Dialog;
    ui.setupUi(this);
}

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yup, memory leak.

[tilm]

Yes, I corrected the mistakes in the way you suggested. But I still get the same compiler error I mentioned above in my first post:

release\MainWindow.o(.text+0x28f):MainWindow.cpp: undefined reference to 'Dialog::Dialog(QWidget*)'

The problem must be somewhere else and I suspect that I am not aware of a property of QMainWindow that prevents me to create an instance of a Dialog inside its member functions. Remember: the same code works in member functions of classes that inherit other QObjects.

I reduced the MainWindow class even further and still get the same error:

class MainWindow : public QMainWindow {
 
public:	
	MainWindow(QWidget *parent=0,Qt::WFlags flags=0);
	void createDialog();
 
private:
	Ui::MainWindow *ui;
};
 
MainWindow::MainWindow(QWidget *parent,Qt::WFlags flags){
	ui = new Ui::MainWindow;
	ui->setupUi(this);
	createDialog();
}
 
void MainWindow::createDialog(){
	Dialog d;
}

class MainWindow : public QMainWindow {
	
public:	
	MainWindow(QWidget *parent=0,Qt::WFlags flags=0);
	void createDialog();
	
private:
	Ui::MainWindow *ui;
};

MainWindow::MainWindow(QWidget *parent,Qt::WFlags flags){
	ui = new Ui::MainWindow;
	ui->setupUi(this);
	createDialog();
}

void MainWindow::createDialog(){
	Dialog d;
}

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[spirit]

can you attach compilable sources?

[jpn]

Do you have dialog.cpp in the .pro file? If not, that would explain why you didn't get compilation errors but managed to pass to the linking stage.

[tilm]

Thanks jpn, this was the problem. I always thought that

qmake -project

was sufficient to create a complete .pro file (I'm sure that I ran it before qmake and make). For me this was the first time that something in a .pro file created with qmake was missing. Do you know the reason for this?

[tilm]

I think I found the answer on my own: 'qmake -project' only includes dialog.cpp into the .pro file when dialog.h is included in MainWindow.h . But I first included the Dialog header file in MainWindow.cpp. That was the reason.