Problem in Connecting ctkDoubleSpinBox

[Meera Hadid]

• I am trying to add an action listener to ctkDoubleSpinBox of qMRMLSliceControllerWidget and change QLabel value in qMRMLSliceWidget.
• I am able to access ctkDoubleSpinBox inside qMRMLSliceWidget and add a connection as shown below.

connect(this->SliceController->spinBox, SIGNAL(valueChanged(double)), this, SLOT(updateLabel()));

void qMRMLSliceWidget::updateLabel()
{
    Q_D(qMRMLSliceWidget);
    d->SpinBoxVal->setText(d->SliceController->spinBox->cleanText());
}

• Error:

'QMetaObject::Connection QObject::connect(const QObject *,const char *,const QObject *,const char *,Qt::ConnectionType)': cannot convert argument 1 from 'ctkDoubleSpinBox *' to 'const QObject *'

• How can I add a connection to ctkDoubleSpinBox?

[jsulm]

@Meera-Hadid said in Problem in Connecting ctkDoubleSpinBox:

ctkDoubleSpinBox

Is it derived from QObject?

[Meera Hadid]

Yes.
ctkDoubleSpinBox class:

class CTK_WIDGETS_EXPORT ctkDoubleSpinBox : public QWidget

[jsulm]

@Meera-Hadid Does it also have Q_OBJECT macro? Like

class MyClass : public QObject
{
    Q_OBJECT

[Meera Hadid]

Yes.

class CTK_WIDGETS_EXPORT ctkDoubleSpinBox : public QWidget
{
  Q_OBJECT
  Q_ENUMS(SetMode)
  Q_FLAGS(DecimalsOption DecimalsOptions)
  Q_ENUMS(SizeHintPolicy)

  Q_PROPERTY(Qt::Alignment alignment READ alignment WRITE setAlignment)
  Q_PROPERTY(bool frame READ hasFrame WRITE setFrame)
  Q_PROPERTY(bool readOnly READ isReadOnly WRITE setReadOnly)
  Q_PROPERTY(QString prefix READ prefix WRITE setPrefix)
  Q_PROPERTY(QString suffix READ suffix WRITE setSuffix)
  Q_PROPERTY(QString cleanText READ cleanText)
 ....

[Christian Ehrlicher]

@Meera-Hadid said in Problem in Connecting ctkDoubleSpinBox:

ctkDoubleSpinBox

Did you also include the header for this class where you do the connect?

[Meera Hadid]

Yes I Did.

#include <ctkDoubleSpinBox.h>

[jsulm]

@Meera-Hadid Try to do the connect using new connect syntax https://doc.qt.io/qt-5/signalsandslots.html

[ChrisW67]

I think Christian meant, did you add the header ctkDoubleSpinBox.h to the HEADERS variable in your PRO file?

Did you run qmake after doing that?
Have you tried a clean rebuild of everything?

[Meera Hadid]

@jsulm

• do you mean this syntax?

 Counter a, b;
    QObject::connect(&a, &Counter::valueChanged,
                     &b, &Counter::setValue);

• I am getting a syntax error when I use this: this->SliceController->&spinBox

[JonB]

@Meera-Hadid said in Problem in Connecting ctkDoubleSpinBox:

I am getting a syntax error when I use this: this->SliceController->&spinBox

This is not legal C++. It should be:

&this->SliceController->spinBox

Whether you want the & depends on whether spinbox is already a pointer or not (I think yours is a pointer, in which case you would not want it?)

[Christian Ehrlicher]

@JonB said in Problem in Connecting ctkDoubleSpinBox:

&this->SliceController->spinBox

But according to the error message

cannot convert argument 1 from 'ctkDoubleSpinBox *' to 'const QObject *

It's already a pointer so the & is wrong.
I still think the header for this class is not included where the connect is done so the compiler doesn't know that ctkDoubleSpinBox is derived from QObject.

[Meera Hadid]

@Christian-Ehrlicher

• I did include #include <ctkDoubleSpinBox.h>

[jsulm]

@Meera-Hadid Fix your connect as suggested by @JonB and try again

[Meera Hadid]

@JonB

• Yes when I tried without using & it was raising an error that cannot convert from 'ctkDoubleSpinBox *' to 'const QObject *'

@jsulm

• The issue is not getting pointer the issue is it cannot convert from 'ctkDoubleSpinBox *' to 'const QObject *'

[JonB]

@Meera-Hadid said in Problem in Connecting ctkDoubleSpinBox:

@JonB

Yes when I tried without using & it was raising an error that cannot convert from 'ctkDoubleSpinBox *' to 'const QObject *'

@jsulm

The issue is not getting pointer the issue is it cannot convert from 'ctkDoubleSpinBox *' to 'const QObject *'

Inserting a & randomly will not help. The message already tells that pointer-ness is not the issue.

[jsulm]

@Meera-Hadid said in Problem in Connecting ctkDoubleSpinBox:

The issue is not getting pointer the issue is it cannot convert from 'ctkDoubleSpinBox *' to 'const QObject *'

Do you mean you get same error message if you use new connect syntax?

[JonB]

@Meera-Hadid
Please do the following:

• First, delete all the files from the build output directory. Do a fresh qmake followed by a build. Does the error still occur?
• From the line number in the error message, are you quite sure it is on the connect() statement you have shown, and not some other?
• I believe I already advised this before in answer to the same problem from you in another thread: on the line above the connect() put in

const QObject *temp = this->SliceController->spinBox;

Does that error (show message)?

[Meera Hadid]

@JonB

• const QObject *temp = this->SliceController->spinBox;
  this works
• But the signal SIGNAL(valueChanged(double)) doesn't get activated (QLabel value doesn't change). Is it because temp is returing nullptr?

[JonB]

@Meera-Hadid

Is it because temp is returing nullptr?

Pardon? Are you saying this->SliceController->spinBox == nullptr at the time you execute the connect() statement?

Separately, put a qDebug() statement as the first thing in your void qMRMLSliceWidget::updateLabel().

[Meera Hadid]

@JonB said in Problem in Connecting ctkDoubleSpinBox:

Separately, put a qDebug() statement as the first thing in your void qMRMLSliceWidget::updateLabel().

Yes I did but that statement is not getting printed/executed

[JonB]

@Meera-Hadid
I have asked you other questions. If you don't want to respond to them that is up to you.

[Meera Hadid]

@JonB

• First, delete all the files from the build output directory. Do a fresh qmake followed by a build. Does the error still occur?
  Since there are a lot of files it takes a lot of time to build hence I did not clear the build.
• It's my bad that I assumed this->SliceController->spinBox was returning a nullptr. The problem was with slot I changed it.
• const QObject *temp = this->SliceController->spinBox; worked for me

Thanks everyone for contributing.