[Qt-interest] How to fix the crash problem when using QGraphicsView on QMainWindow with QLineEdit

[Steven Chang]

Dear Alex,

Thanks a lot for your kindly helps.
It works and never crashes again.

Best Regards,
Steven

-----Original Message-----
From: qt-interest-bounces at trolltech.com [mailto:qt-interest-bounces at trolltech.com] On Behalf Of Malyushytsky, Alex
Sent: Wednesday, May 05, 2010 3:18 AM
To: qt-interest at trolltech.com
Subject: Re: [Qt-interest] How to fix the crash problem when using QGraphicsView on QMainWindow with QLineEdit

1. First I would highly recommend change allocation of the all QObjects derived classes which might have parent or may be re-parented.
Otherwise parent will attempt to delete it child.

For example:

It looks like that you are trying to show MainWindow in the QGraphicsScene (I would expect to see QGraphicsView in MainWindow), so replace
"MainWindow w;" with "MainWindow* w = new MainWindow;" ,

gView.setScene(&gScene); // will reparent gScene to QGraphicsView gView;
Due to code above you have to replace QGraphicsScene gScene; with a code which allows gView delete gScene when it is destroyed:
QGraphicsScene* gScene = new QGraphicsScene();


All above may not solve your current problems but sure will cause problem later. Your application mostly likely will always crash on exit.

2. I highly recommend to play with Qt Designer constructing QMainWindow and other widgets, inspecting the code it generates at least for purpose of learning.

I don't think code you wrote in  MainWindow should cause crash, but it does not make any sense either.

I would recommend you to fix the problem I mentioned above first.
If your main routine can be modified as below it should work.

int main(int argc, char *argv[])
{
        QApplication a(argc, argv);


    QGraphicsScene* gScene= new QGraphicsScene();
        tst* w = new tst();
    gScene->addWidget( w );

    QGraphicsView gView;
    gView.setScene(gScene);
    gView.adjustSize();
    gView.show();


        a.connect(&a, SIGNAL(lastWindowClosed()), &a, SLOT(quit()));
        return a.exec();
}


Hope this helps,
    Alex

-----Original Message-----
From: qt-interest-bounces at trolltech.com [mailto:qt-interest-bounces at trolltech.com] On Behalf Of Steven Chang
Sent: Tuesday, May 04, 2010 10:27 AM
To: qt-interest at trolltech.com
Subject: [Qt-interest] How to fix the crash problem when using QGraphicsView on QMainWindow with QLineEdit

Dear Sir,

I created a QLineEdit in QMainWindow class as below:

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
    lineEdit = new QLineEdit(this);
}

Then I created a QGraphicsView and QGraphicsScene in main.cpp and set
MainWindow as the view widget.

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    QGraphicsScene gScene;
    gScene.addWidget(&w);
    QGraphicsView gView;
    gView.setScene(&gScene);
    gView.adjustSize();
    gView.show();
    return a.exec();
}

But after built the App and executed it, the App would crash if I type any
character in lineEdit.
How do I fix this problem?

Best Regards,
Steven

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