form on create function

freevrs

i got a sigsegv

it is segfaulting at the wizard() in the constructor

But i dont get why, because i call it the same way later on (in the click funktions) and everything is fine

jsulm

@freevrs As far as I can see wizard() returns a pointer. Is it possible that it returns an invalid pointer? And does it crash inside wizard()?

freevrs

@jsulm

this is the complete stack trace

Thread 1 (Thread 9460.0x2030):
#0  0x0accbeac in QScopedPointer<QObjectData, QScopedPointerDeleter<QObjectData> >::data (this=0x4) at ../../include/QtCore/../../src/corelib/tools/qscopedpointer.h:135
No locals.
#1  0x0aae7e74 in qGetPtrHelper<QScopedPointer<QObjectData> > (p=...) at ../../include/QtCore/../../src/corelib/global/qglobal.h:983
No locals.
#2  0x0acf8d57 in QWizard::d_func (this=0x0) at dialogs/qwizard.h:193
No locals.
#3  0x0aae5b9f in QWizard::button (this=0x0, which=QWizard::NextButton) at dialogs\qwizard.cpp:2818
        d = 0x15b6de38
#4  0x00401df8 in WizardPage2::WizardPage2 (this=0x15b6dc78, parent=0x0) at ..\SPAPP-Screen\wizardpage2.cpp:10
No locals.
#5  0x00401711 in qMain (argc=1, argv=0x9c3578) at ..\SPAPP-Screen\main.cpp:26
        a = {<QGuiApplication> = {<QCoreApplication> = {<QObject> = {_vptr.QObject = 0xadf7f88 <vtable for QApplication+8>, static staticMetaObject = {d = {superdata = 0x0, stringdata = 0x6bb73880 <qt_meta_stringdata_QObject>, data = 0x6bb73980 <qt_meta_data_QObject>, static_metacall = 0x6b90941e <QObject::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>, relatedMetaObjects = 0x0, extradata = 0x0}}, d_ptr = {d = 0x9c3628}, static staticQtMetaObject = {d = {superdata = 0x0, stringdata = 0x6bc32900 <qt_meta_stringdata_Qt>, data = 0x6bc3b040 <qt_meta_data_Qt>, static_metacall = 0x0, relatedMetaObjects = 0x0, extradata = 0x0}}}, static staticMetaObject = {d = {superdata = 0x6bb7340c <QObject::staticMetaObject>, stringdata = 0x6bc47600 <qt_meta_stringdata_QCoreApplication>, data = 0x6bc477c0 <qt_meta_data_QCoreApplication>, static_metacall = 0x6b9693e4 <QCoreApplication::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>, relatedMetaObjects = 0x0, extradata = 0x0}}, static self = 0x28fe3c}, static staticMetaObject = {d = {superdata = 0x6bc47584 <QCoreApplication::staticMetaObject>, stringdata = 0xf7ee00 <qt_meta_stringdata_QGuiApplication>, data = 0xf7f200 <qt_meta_data_QGuiApplication>, static_metacall = 0xb4e2bc <QGuiApplication::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>, relatedMetaObjects = 0x0, extradata = 0x0}}}, static staticMetaObject = {d = {superdata = 0xf75040 <QGuiApplication::staticMetaObject>, stringdata = 0xad1f4c0 <qt_meta_stringdata_QApplication>, data = 0xad1f740 <qt_meta_data_QApplication>, static_metacall = 0xa8c1134 <QApplication::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>, relatedMetaObjects = 0x0, extradata = 0x0}}}
        w = {<QMainWindow> = {<QWidget> = {<QObject> = {_vptr.QObject = 0x40cfc8 <vtable for MainWindow+8>, static staticMetaObject = {d = {superdata = 0x0, stringdata = 0x6bb73880 <qt_meta_stringdata_QObject>, data = 0x6bb73980 <qt_meta_data_QObject>, static_metacall = 0x6b90941e <QObject::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>, relatedMetaObjects = 0x0, extradata = 0x0}}, d_ptr = {d = 0x9cdf78}, static staticQtMetaObject = {d = {superdata = 0x0, stringdata = 0x6bc32900 <qt_meta_stringdata_Qt>, data = 0x6bc3b040 <qt_meta_data_Qt>, static_metacall = 0x0, relatedMetaObjects = 0x0, extradata = 0x0}}}, <QPaintDevice> = {_vptr.QPaintDevice = 0x40d0a4 <vtable for MainWindow+228>, painters = 0, reserved = 0x0}, static staticMetaObject = {d = {superdata = 0x6bb7340c <QObject::staticMetaObject>, stringdata = 0xad25b40 <qt_meta_stringdata_QWidget>, data = 0xad265c0 <qt_meta_data_QWidget>, static_metacall = 0xa8fc0ec <QWidget::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>, relatedMetaObjects = 0x0, extradata = 0x0}}, data = 0x9ce020}, static staticMetaObject = {d = {superdata = 0xad1c060 <QWidget::staticMetaObject>, stringdata = 0xade7280 <qt_meta_stringdata_QMainWindow>, data = 0xade75c0 <qt_meta_data_QMainWindow>, static_metacall = 0xabf8e1c <QMainWindow::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>, relatedMetaObjects = 0xade776c <qt_meta_extradata_QMainWindow>, extradata = 0x0}}}, static staticMetaObject = {d = {superdata = 0xade7218 <QMainWindow::staticMetaObject>, stringdata = 0x40c4c4 <qt_meta_stringdata_MainWindow>, data = 0x40c4e0 <qt_meta_data_MainWindow>, static_metacall = 0x402220 <MainWindow::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>, relatedMetaObjects = 0x0, extradata = 0x0}}, ui = 0x9ceb50}
        setupcomplete = false
        wizard = {<QDialog> = {<QWidget> = {<QObject> = {_vptr.QObject = 0xae074c8 <vtable for QWizard+8>, static staticMetaObject = {d = {superdata = 0x0, stringdata = 0x6bb73880 <qt_meta_stringdata_QObject>, data = 0x6bb73980 <qt_meta_data_QObject>, static_metacall = 0x6b90941e <QObject::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>, relatedMetaObjects = 0x0, extradata = 0x0}}, d_ptr = {d = 0x15b52298}, static staticQtMetaObject = {d = {superdata = 0x0, stringdata = 0x6bc32900 <qt_meta_stringdata_Qt>, data = 0x6bc3b040 <qt_meta_data_Qt>, static_metacall = 0x0, relatedMetaObjects = 0x0, extradata = 0x0}}}, <QPaintDevice> = {_vptr.QPaintDevice = 0xae075c4 <vtable for QWizard+260>, painters = 0, reserved = 0x0}, static staticMetaObject = {d = {superdata = 0x6bb7340c <QObject::staticMetaObject>, stringdata = 0xad25b40 <qt_meta_stringdata_QWidget>, data = 0xad265c0 <qt_meta_data_QWidget>, static_metacall = 0xa8fc0ec <QWidget::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>, relatedMetaObjects = 0x0, extradata = 0x0}}, data = 0x15b52340}, static staticMetaObject = {d = {superdata = 0xad1c060 <QWidget::staticMetaObject>, stringdata = 0xad5b0c0 <qt_meta_stringdata_QDialog>, data = 0xad5b240 <qt_meta_data_QDialog>, static_metacall = 0xaab1464 <QDialog::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>, relatedMetaObjects = 0x0, extradata = 0x0}}}, static staticMetaObject = {d = {superdata = 0xad5afcc <QDialog::staticMetaObject>, stringdata = 0xad64a80 <qt_meta_stringdata_QWizard>, data = 0xad65040 <qt_meta_data_QWizard>, static_metacall = 0xaae748c <QWizard::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>, relatedMetaObjects = 0x0, extradata = 0x0}}}
#6  0x00403b50 in WinMain@16 () at qtmain_win.cpp:113
        argc = 1
        argvW = 0xa3c200
        argv = 0x9c3578
        exitCode = 119
#7  0x004066ed in main ()
No symbol table info available.

is it maby that because the wizard is created in the main.cpp

QWizard wizard;
    wizard.setWindowTitle("Setup");
    wizard.addPage(new WizardPage1());
    wizard.addPage(new WizardPage2());
    wizard.addPage(new WizardPage3());
    wizard.show();

and the wizardpacge2 is compiled before that , that wthe wizard() does not exist at this moment ?

jsulm

@freevrs

#3  0x0aae5b9f in QWizard::button (this=0x0, which=QWizard::NextButton) at dialogs\qwizard.cpp:2818
        d = 0x15b6de38
#4  0x00401df8 in WizardPage2::WizardPage2 (this=0x15b6dc78, parent=0x0) at ..\SPAPP-Screen\wizardpage2.cpp:10
No locals.

Can you show the code in wizardpage2.cpp around the line 10?
In this line I can see that this is null:

#3  0x0aae5b9f in QWizard::button (this=0x0, which=QWizard::NextButton) at dialogs\qwizard.cpp:2818
        d = 0x15b6de38

And can you please explain what wizard() is doing? Wizard itself already exists when you create WizardPage2.

jsulm

@freevrs "and the wizardpacge2 is compiled before that , that wthe wizard() does not exist at this moment" I don't understand this sentence.
First, wizardpacge2 is not compiled - it is instantiated/created.
Second, "wizard() does not exist at this moment" - wizard() is a method, so it exists.

freevrs

@jsulm

wizard() is a method i can use after the wizardpage is created.

with that i can access elements of the wizard box (like buttons)

the wizard is created in the main function and than the wizard pages get added.

so i dont understand why i cant use it in the creator

http://doc.qt.io/qt-4.8/qwizard.html
http://doc.qt.io/qt-5/qwizardpage.html
http://www.qtcentre.org/threads/13844-How-to-disable-NextButton-in-QWizard

jsulm

@freevrs Please read the documentation (http://doc.qt.io/qt-5/qwizardpage.html#wizard):

Returns the wizard associated with this page, or 0 if this page hasn't been inserted into a QWizard yet.

QWizard wizard;
wizard.addPage(new WizardPage2());

new WizardPage2() creates a new instance and calls its constructor - at that time the wizard is not yet set, it is set when wizard.addPage(...) is called which happens after the constructor was executed. That's why wizard() returns a null pointer in constructor.

freevrs

@jsulm

ok .. but how can i solve this ?

can i create a slot that is called on the addPage event an then call wizard() ?
Or do you have a better idea / solution for that.

What i need to achive is, that when the wizzard page is shown the next button is disabled

jsulm

@freevrs You can overwrite http://doc.qt.io/qt-5/qwidget.html#showEvent

kshegunov

@freevrs

You can intercept the widget parent's swap by handling the QEvent::ParentChange. Also you can queue the initialization for later when control returns to the event loop, which would by my preference, e.g.:

class WizardPage2
{
public:
    WizardPage2(QWidget * parent);

private:
     Q_INVOKABLE void initMyPage();
};

WizardPage2::WizardPage2(QWidget * parent)
    : QWizardPage(parent)
{
    QMetaObject::invokeMethod(this, "initMyPage", Qt::QueuedConnection);
}

void WizardPage2::initMyPage()
{
    // wizard() should be pointing to an object now.
}

SGaist

Hi,

But why disable the wizard button in the constructor of the second page ? That's rather the role of the page validation. See QWizard::validateCurrentPage documentation.

freevrs

@kshegunov

Your solution works pretty good.

I implemented it on page2
but insted it is only setting the button on page 1 (not implemented there)
and not on page2

Do i need to use another event ?