Trouble with signals and slots

Gmin Gnay

connect(m_mainButton,&QPushButton::clicked,this,&ImageCorrectButton::selectImageFile);

Dose "this" class contain "ImageCorrectButton::selectImageFile" slot?

J.Hilk

how about giving us a bit more information? E.g. what does the crashreport say?

anyway, what is parent in

QPushButton *m_mainButton = new QPushButton("Click to \n &Select Image",parent) ;

does it also crash if you change it to

QPushButton *m_mainButton = new QPushButton("Click to \n &Select Image",nullptr) ;

?

gabor53

Hi,
Yes, the "this" class contains "ImageCorrectButton::selectImageFile" slot.
Switching from parent to nullptr doesn't change the behavior.

The reports:
Locals
m_mainButton @0x12395cc QPushButton
parent @0x12395f0 QWidget
this @0x123957c ImageCorrectButton
The program stops at the connect.

jsulm

@gabor53 In the first post you said that the slot was called ("but the m_mainButton clicked message is displayed), now you say it is hanging on the connect. Can you please describe the issue clearly?
If the slot was called then the connect was successful and the problem is somewhere else. You should debug your app to see where exactly it hangs.

VRonin

@gabor53 said in Trouble with signals and slots:

The program stops at the connect.

Define "stops"

crashes
doesn't compile
hangs (i.e. looks like an infinite loop)

gabor53

@VRonin
Hangs describes it the best. Nothing happens even when I click the button again. It feels like it doesn't want to go to the slot. I can click on other buttons after it hangs and does what ever it is supposed to do.

VRonin

ok, try replacing connect(m_mainButton,&QPushButton::clicked,this,&ImageCorrectButton::selectImageFile); with connect(m_mainButton,&QPushButton::clicked,[]()->void{qDebug("Entered selectImageFile!");}); and see if that works

gabor53

@VRonin
Nothing new happens. "Hangs" at the same location.

VRonin

Nothing gets printed in the debug console?!

gabor53

@VRonin
Entered createEditor
Entered image editor
Entered ImageCorrectButton!
m_mainButton clicked!

Locals		
	m_mainButton	@0x12395cc	QPushButton
	parent	@0x12395f0	QWidget
	this	@0x123957c	ImageCorrectButton

1 ImageCorrectButton::ImageCorrectButton 2 myDelegate::createEditor 3 QAbstractItemViewPrivate::editor 4 QAbstractItemViewPrivate::openEditor 5 QAbstractItemView::edit 6 QAbstractItemView::mouseDoubleClickEvent 7 QWidget::event 8 QFrame::event 9 QAbstractScrollArea::viewportEvent 10 QAbstractItemView::viewportEvent 11 QAbstractScrollAreaPrivate::viewportEvent 12 QAbstractScrollAreaFilter::eventFilter 13 QCoreApplicationPrivate::sendThrou 14 QApplicationPrivate::notify_helper 15 QApplication::notify 16 QCoreApplication::notifyInternal2 17 QCoreApplication::sendSpontaneousEvent 18 QApplicationPrivate::sendMouseEvent 19 QWidgetWindow::handleMouseEvent 20 QWidgetWindow::event ... <More> imagecorrectbutton.cpp 16 0x41e080
mydelegate.cpp 49 0x41c61a
qabstractitemview.cpp 4199 0x15154af1
qabstractitemview.cpp 4384 0x15155895
qabstractitemview.cpp 2676 0x1514fa8e
qabstractitemview.cpp 1954 0x1514cf86
qwidget.cpp 8789 0x14f26e82
qframe.cpp 550 0x1503c188
qabstractscrollarea.cpp 1213 0x150c1a09
qabstractitemview.cpp 1747 0x1514bd6a
qabstractscrollarea_p.h 111 0x1528ad14
qabstractscrollarea_p.h 127 0x15289b35
ghObjectEventFilters qcoreapplication.cpp 1099 0x1e4ca0e
qapplication.cpp 3795 0x14eefb50
qapplication.cpp 3273 0x14eed8b8
qcoreapplication.cpp 988 0x1e4c6e7
qcoreapplication.h 234 0x1526c865
qapplication.cpp 2769 0x14eec563
qwidgetwindow.cpp 617 0x14f3fb2a
qwidgetwindow.cpp 239 0x14f3e75e

VRonin

ok, let's bring out the guns:
use connect(m_mainButton,&QPushButton::clicked,[]()->void{Q_ASSERT(false);}); this should crash your program (actually assert but stay with me here) as soon as you press m_mainButton

[Make sure you compile in debug mode and not release]

gabor53

@VRonin
Nothing happened. Behaves the same way as before.

VRonin

shame on me, it was so obvious and I missed it: QPushButton *m_mainButton = new QPushButton("Click to \n &Select Image",parent) ; you are shadowing your member, use m_mainButton = new QPushButton("Click to \n &Select Image",this) ;

gabor53

@VRonin said in Trouble with signals and slots:

m_mainButton = new QPushButton("Click to \n &Select Image",this) ;

This is the message I get in output:

Entered createEditor
Entered image editor
Entered ImageCorrectButton!
m_mainButton clicked!
ASSERT: "false" in file ..\Folkfriends_1_0\imagecorrectbutton.cpp, line 18

This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.
C:\Programming\Projects\build-Folkfriends_1_0-Desktop_Qt_5_7_0_MinGW_32bit-Debug\debug\Folkfriends_1_0.exe exited with code 3

VRonin

we found the problem then.
you can now go back to connect(m_mainButton,&QPushButton::clicked,this,&ImageCorrectButton::selectImageFile); and it should work

gabor53

@VRonin said in Trouble with signals and slots:

connect(m_mainButton,&QPushButton::clicked,this,&ImageCorrectButton::selectImageFile)

Thank you. It works now. What was actually wrong with it?

jsulm

@gabor53 As @VRonin said you created another button with same name as in your class:

// m_mainButton is a new local variable with same name as in the class
QPushButton *m_mainButton = new QPushButton("Click to \n &Select Image",parent) ;

In your class you have

QPushButton *m_mainButton;

right?
But then you create a new one with same name. You just need to remove QPushButton* like this to use m_mainButton from your class:

// m_mainButton from the class
m_mainButton = new QPushButton("Click to \n &Select Image",parent) ;

So, you did the connection with another button (not the one which is visible).