Writing to a QListWidget from OpenCV window - qt

Question

I am writing an application for manually selecting regions of interest from an image. Two windows will appear:
An OpenCV window, where the user should select a ROI with the mouse.
A QT window, where the selected ROI's coordinates will appear (in a QListWidget)
My problem is how to write onto the QListWidget of the QT window from the OpenCV mouse listener. I guess I have to write a function inside my QT class that returns a pointer to the QListWidget, but I havent managed to do it.
Can someone please point me in the right direction?
Here is my main:
#include "myclass.h"
#include <QApplication>
#include </PathToOPENCV/opencv/cv.h>
#include </PathToOPENCV/opencv/highgui.h>
#include <QtDebug>
#include <QListWidget>
using namespace cv;
// Pointer to list widget? Should I use it as a global variable to recieve the pointer of the QListWidget?
QListWidget * ptrToList;
void mouseEvent(int evt, int x, int y, int flags, void* param){
if( evt == CV_EVENT_LBUTTONUP){
// WRITE HERE ONTO QListWidget!
// Something like:
ptrToList->addItem("blah");
}
}
int main(int argc, char *argv[])
{
/*----- OPENCV STUFF ----*/
String windowName = "selectionWindow";
namedWindow( windowName , CV_WINDOW_NORMAL);
Mat theImage = imread("/PATHTOIMAGE/1.jpg");
imshow( windowName,theImage );
/* ---- Mouse Listener setup ----- */
setMouseCallback( windowName, mouseEvent , 0 );
/* ---- QT Stuff ---- */
QApplication a(argc, argv);
myClass w;
w.show();
// Should I do something like this?
ptrToList = w->getListPtr("listWidget");
return a.exec();
}
Here is myclass.h
namespace Ui {
class myClass;
}
class myClass : public QMainWindow
{
Q_OBJECT
public:
explicit myClass(QWidget *parent = 0);
~myClass();
private:
Ui::myClass *ui;
QListWidget * getListPtr(QString listName){
QListWidget * theList;
// None of these work...
//theList = this->parent()->getChild( listName );
//theList = this->getChild( listName );
return(theList);
}
};
EDIT:
#Roku,
I tried your suggestion, but I think I did it wrong. I added a function in myclass for setting up the mouse callback, so myclass.h is like this:
#include <functions.cpp>
using namespace cv;
namespace Ui {
class myClass; /* error: forward declaration of 'struct Ui::myClass' */
}
class myClass : public QMainWindow
{
Q_OBJECT
public:
explicit myClass(QWidget *parent = 0);
~myClass();
void setInnerMouseCallback(String windowName){
setMouseCallback( windowName, mouseEvent , ui->listWidget ); /* error: invalid use of incomplete type 'struct Ui::myClass'*/
}
private:
Ui::myClass *ui;
}
Then, I added a functions.cpp file with the following code:
void mouseEvent(int evt, int x, int y, int flags, void* param){
QListWidget * theList = (QListWidget*) param;
if( evt == CV_EVENT_LBUTTONUP){
theList->addItem("blah");
}
}
Is this correct? I get a couple of errors where pointed. Thank you for your help.

Answer 1

The third parameter of the setMouseCallback() is called as "user data" and its type is void*. It is designed to be used for just this kind of information. You could to move the setMouseCallback() function call to your main window. And then you could use the function like this:
setMouseCallback(windowName, mouseEvent, ui->listWidget);
In the mouse event callback function you would have a pointer to the list widget:
void mouseEvent(int evt, int x, int y, int flags, void* param)
{
if( evt == CV_EVENT_LBUTTONUP)
{
QListWidget* listWidget = (QListWidget*)param;
listWidget->addItem("blah");
}
}