(Qt) Unusable window after one button click - qt

Question

I have a window with many buttons. Each one triggers a sub-program (written using the Opencv API). Each sub-program displays images and stuff on windows.
The problem is, when I close these windows (via the little red cross), all the buttons become unclickable. So if I want to launch another program, I'll have to exit the main window and run it again.
In other words, I want to be able to run all the sub-programs without having to start over every time.
Here's the GUI's code :
.cpp
#include "fenprincipale.h"
#include "ui_fenprincipale.h"
#include<highgui.h>
#include<cv.h>
#include <moyenetmedian.h>
#include<morpho.h>
#include<tracking.h>
#include<contour.h>
#include<QApplication>
FenPrincipale::FenPrincipale(QWidget *parent) :
QWidget(parent),
ui(new Ui::FenPrincipale)
{
ui->setupUi(this);
MoyenEtMedian *moyenEtMedian = new MoyenEtMedian;
morpho * mor = new morpho;
tracking * tra= new tracking;
contour * cont= new contour;
QObject::connect(ui->bMoyMed, SIGNAL( clicked() ), moyenEtMedian, SLOT( exec() ), Qt::AutoConnection );
QObject::connect(ui->bMorph, SIGNAL( clicked() ), mor, SLOT( exec() ), Qt::AutoConnection );
QObject::connect(ui->bTrack, SIGNAL( clicked() ), tra, SLOT( exec() ), Qt::AutoConnection );
QObject::connect(ui->bCont, SIGNAL( clicked() ), cont, SLOT( exec() ), Qt::AutoConnection );
}
FenPrincipale::~FenPrincipale()
{
delete ui;
}
.h :
#ifndef FENPRINCIPALE_H
#define FENPRINCIPALE_H
#include <QWidget>
#include <QApplication>
namespace Ui {
class FenPrincipale;
}
class FenPrincipale : public QWidget
{
Q_OBJECT
public:
explicit FenPrincipale(QWidget *parent = 0);
void switch_callback(int);
void execMoyMed (void);
~FenPrincipale();
private:
Ui::FenPrincipale *ui;
};
#endif // FENPRINCIPALE_H
the main class :
#include <QCoreApplication>
#include <QApplication>
#include <QtGui>
#include <QWidget>
#include "fenprincipale.h"
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
FenPrincipale fenetre;
fenetre.show();
return a.exec();
}
Slot implementation for "moyenetmedian" :
void MoyenEtMedian::exec(void)
{
const char* name = "Filtres";
IplImage* img = cvLoadImage( "C:/Users/XELTINFO/ProjetVision/image.png" );
IplImage* out = cvCreateImage( cvGetSize(img), IPL_DEPTH_8U, 3 );
cvNamedWindow( name, 1 );
cvShowImage(name, out);
// Create trackbar
cvCreateTrackbar2( "Filtre", name, &g_switch_value, 1, &MoyenEtMedian::switch_callback, this );
while( 1 ) {
switch( filterInt ){
case 0:
cvSmooth( img, out, CV_BLUR, 7, 7 );
break;
case 1:
cvSmooth( img, out, CV_MEDIAN, 7, 7 );
break;
}
if(filterInt != lastfilterInt){
cvShowImage(name, out);
lastfilterInt = filterInt;
}
if( cvWaitKey( 15 ) == 27 )
break;
}
cvReleaseImage( &img );
cvReleaseImage( &out );
cvDestroyWindow( name );
}
The class declaration :
#ifndef MOYENETMEDIAN_H
#define MOYENETMEDIAN_H
#include "ui_fenprincipale.h"
#include<QObject>
class MoyenEtMedian : public QObject
{
Q_OBJECT
public:
MoyenEtMedian();
static void switch_callback(int position, void*);
public slots :
void exec(void);
};
#endif // MOYENETMEDIAN_H
The class delcarations and slots implementations are very similar for all classes. I'll add the rest if this isn't enough.

Answer 1

You are blocking the event loop in your exec() slot, since it doesn't return immediately. You should instead subclass QWidget and override keyPressEvent() to get keyboard input from Qt's event loop instead of doing the busy-loop you currently have.

Answer 2

So when using Qt with OpenCV, I would setup the polling using Qt's timers instead of a while loop.
There is a pretty good tutorial of using QTimers to interact with OpenCV objects here:
http://www.youtube.com/watch?v=0ONxIy8itRA
Jump to 35 or 38 minutes into it to see how he writes his classes.
Basically, you let Qt do the waiting and timing, instead of having a while loop with a wait call doing the timing.
And if possible, let Qt create the windows, and nest the OpenCV windows into Qt's windows so that Qt can manage the events on the windows.
Hope that helps.