slot valueChanged(double) of doubleSpinBox called twice if breakpoint is set

[Marco W.]

Hi there,

I created a simple GUI Application using QT Creator 2.6 and MSVC2010 with CDB on a Win7 SP1 32-Bit system.

The QUI was created by QT Designer and has a doubleSpinBox. I setup the slot

valueChanged(double)

valueChanged(double)

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of the doubleSpinBox. The slot is connected via

connectSlotsByName

connectSlotsByName

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.

Everything works fine, but if I set a breakpoint in the slot

doubleSpinBox_valueChanged(double arg1)
{
}

doubleSpinBox_valueChanged(double arg1)
{
}

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there is a strange behaviour:

On a click on the arrows of the doubleSpinbox the slot

doubleSpinBox_valueChanged(double arg1)

doubleSpinBox_valueChanged(double arg1)

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is called TWICE and of course the value-property of the doubleSpinBox is incremented/decremented twice!
I verified this by adding a

qDebug << "doubleSpinBox_valueChanged hit"

qDebug << "doubleSpinBox_valueChanged hit"

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to the slot.




Is this a known issue?

Thanks for your help in advance!

[wysota]

valueChanged() signal does not cause anything to be incremented or decremented. Could you explain better what you mean?

[Marco W.]

Hi wysota,

sorry if didn't make things clear. I will try to do it better:

I set a breakpoint in the slot valueChanged(double) of the doubleSpinBox. When I debug my GUI application and I click on the arrow-up-icon of the doubleSpinbox, then the breakpoint in the valueChanged(double)-Slot is hit and the old value is incremented as it should. But by clicking on F5 to continue the debugging, the breakpoint is hit again and the value of the doubleSpinBox is incremented again, i.e. twice!
As I sad, I also added a qDebug << "doubleSpinBox_valueChanged hit" in the valueChanged(double)-Slot and the message appears twice in the debugger output!

This happens only if a breakpoint is set in the valueChanged(double)-Slot. When I debug my GUI application without setting a breakpoint in the Slot, then by clickung on the arrow-up-icon the value is incremented only once and of course my qDebug-Message (as menitioned before) appears only once.

I hope that things became more clear.
Thanks for your help!

[wysota]

I set a breakpoint in the slot valueChanged(double) of the doubleSpinBox.

There is no such slot. valueChanged() is a signal. Make up your mind -- are you setting a breakpoint in the valueChanged() signal in QDoubleSpinBox or in a on_doubleSpinBox_valueChanged slot connected to that signal?

[Marco W.]

Oh, ok maybe I mixed it up.

I created a slot for the valueChanged() signal by right-clicking on the doubleSpinBox and selecting "Go to slot..." in QT Designer. The corresponding Signal and Slot are connected via QMetaObject::connectSlotsByName(MainWindow). This happens in the header file for the GUI (created by QT Designer).

So, in fact, it is the on_doubleSpinBox_valueChanged(double arg1) slot where I set my breakpoint.

Sorry for this inaccuracy and again thanks for helping me.

[wysota]

In that case it is not possible that the slot is executed twice if you set a breakpoint on it. If the slot is executing twice then it means you have two connections to it.

[Marco W.]

Well, but the slot is executed twice (and the value of the QdoubleSpinBox is incremented twice), if I set a breakpoint on it. I verified this by adding the qDebug() and printing a message to the debugger output.

If there is no breakpoint set, then the message is printed only once (and the value of the QdoubleSpinBox is incremented only once).


Is it possible that my Debugging Setup has some problems? Sometimes I get a message like:

*** WARNING: Unable to verify checksum for C:\Qt\Qt5.0.1\5.0.1\msvc2010\lib\Qt5Cored.dll
*** WARNING: Unable to verify checksum for C:\Qt\Qt5.0.1\5.0.1\msvc2010\lib\Qt5Widgetsd.dll
*** WARNING: Unable to verify checksum for C:\Qt\Qt5.0.1\5.0.1\msvc2010\lib\Qt5Guid.dll
*** WARNING: Unable to verify checksum for C:\Qt\Qt5.0.1\5.0.1\msvc2010\plugins\platforms\qwi ndowsd.dll

or

*** WARNING: Unable to verify checksum for MyApplicationName.exe

or (because I'm doing some openCV stuff)

*** WARNING: Unable to verify checksum for C:\opencv243\build\x86\vc10\bin\opencv_highgui243d .dll
*** ERROR: Symbol file could not be found. Defaulted to export symbols for C:\opencv243\build\x86\vc10\bin\opencv_highgui243d .dll -
*** WARNING: Unable to verify checksum for C:\Qt\Qt5.0.1\5.0.1\msvc2010\lib\Qt5Guid.dll
*** WARNING: Unable to verify checksum for C:\Qt\Qt5.0.1\5.0.1\msvc2010\lib\libGLESv2d.dll
*** ERROR: Symbol file could not be found. Defaulted to export symbols for C:\Qt\Qt5.0.1\5.0.1\msvc2010\bin\icuuc49.dll -
*** WARNING: Unable to verify checksum for MyApplicationName.exe

Thanks

[wysota]

Well, but the slot is executed twice (and the value of the QdoubleSpinBox is incremented twice), if I set a breakpoint on it. I verified this by adding the qDebug() and printing a message to the debugger output.

That's no proof. Show me the backtrace which shows that the slot is called twice.