Trouble with signals and slots

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

[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).