QItemEditorCreatorBase with custom enum

[InTheBeninging]

Can someone give me a working example how to build a custom editor factory for a QComboBox with a custom enum as data? I tried following this example, but It won't work.
My Code Looks like this:

//hpp
Q_DECLARE_METATYPE(EnumType)

class EnumTypeComboBox : public QComboBox {
    Q_OBJECT
    Q_ENUM(EnumType)
    Q_PROPERTY(EnumType enumType READ enumType WRITE setEnumType USER true)
public:
    EnumTypeComboBox (QWidget *widget = nullptr);
    EnumType enumType() const;
    void setEnumType (const EnumType &enumType);
private:
    void populateList();
};

//cpp
EnumTypeComboBox::EnumTypeComboBox (QWidget *widget) : QComboBox(widget) {
    populateList();
}

EnumType EnumTypeComboBox::enumType() const {
    return qvariant_cast<EnumType>(itemData(currentIndex(), qMetaTypeId<EnumType>()));
}

void EnumTypeComboBox::setEnumType(const EnumType &enumType) {
    setCurrentIndex(findData(enumType, qMetaTypeId<EnumType>()));
}

void EnumTypeComboBox::populateList() {
    addItem("First Type",EnumType::FirstType);
}

//registration
QItemEditorFactory * factory = new QItemEditorFactory;

QItemEditorCreatorBase * enumTypeCreator=
    new QStandardItemEditorCreator<EnumTypeComboBox>();

factory->registerEditor(qMetaTypeId<EnumType>(), enumTypeCreator);

QItemEditorFactory::setDefaultFactory(factory);

It gives me 4 of these Linker Errors:
editorwidget.obj:-1: Fehler: LNK2001: Nicht aufgelöstes externes Symbol ""public: static struct QMetaObject const EnumTypeComboBox::staticMetaObject" (?staticMetaObject@EnumTypeComboBox@@2UQMetaObject@@B)".

Things that are not clear to me:
The enum is included from a seperate header file. Can I even use it as Q_ENUM in my own class? Doesn't it say it adds the enum to a qmetatype automatically? Doing so results in the C:\Qt\5.15.2\msvc2019\include\QtCore\qmetatype.h:1916: Fehler: C2338: Type is not registered, please use the Q_DECLARE_METATYPE macro to make it known to Qt's meta-object system Error.

[InTheBeninging]

Ok it works now. It just needed some changes.
I had to change the property function to save the data with the Qt::UserRole. I guess because the QComboBox::addItem(QString text, QVariant userData) function used to populate the box uses the Qt::UserRole by default.

cv::ThresholdTypes CVThresholdTypeComboBox::threshType() const {
    return qvariant_cast<cv::ThresholdTypes>(itemData(currentIndex(), Qt::UserRole));
}

void CVThresholdTypeComboBox::setThreshType(const cv::ThresholdTypes &threshType) {
    setCurrentIndex(findData(threshType, Qt::UserRole));
}

The conversion function to get a string representation of my custom metatype looks as follows.

QString CVThresholdTypeComboBox::thresholdToString(const cv::ThresholdTypes &threshType) {
    switch(threshType) {
    case cv::THRESH_BINARY:     return "Binary";
    case cv::THRESH_BINARY_INV: return "Binary Inverted";
    case cv::THRESH_TRUNC:      return "Truncated";
    case cv::THRESH_TOZERO:     return "To Zero";
    case cv::THRESH_TOZERO_INV: return "To Zero Inverted";
    case cv::THRESH_MASK:       return "Mask";
    case cv::THRESH_OTSU:       return "Otsu";
    case cv::THRESH_TRIANGLE:   return "Triangle";
    default:                    return "Default";
    }
}

The conversion function is registered with this function.

QMetaType::registerConverter<cv::ThresholdTypes, QString>(&CVThresholdTypeComboBox::thresholdToString);

[Christian Ehrlicher]

@InTheBeninging said in QItemEditorCreatorBase with custom enum:

CVThresholdTypeComboBox

This can not come from the class you are showing above...

[InTheBeninging]

@Christian-Ehrlicher It is. I just forgot to change it's name :D

[Christian Ehrlicher]

@InTheBeninging please post actual code. How should we know that you did not forgot or add something?
Is the moc file beeing generated? I would guess not.

[InTheBeninging]

@Christian-Ehrlicher

imgproc.hpp the enum from opencv

//! type of the threshold operation
//! ![threshold types](pics/threshold.png)
enum ThresholdTypes {
    THRESH_BINARY     = 0, //!< \f[\texttt{dst} (x,y) =  \fork{\texttt{maxval}}{if \(\texttt{src}(x,y) > \texttt{thresh}\)}{0}{otherwise}\f]
    THRESH_BINARY_INV = 1, //!< \f[\texttt{dst} (x,y) =  \fork{0}{if \(\texttt{src}(x,y) > \texttt{thresh}\)}{\texttt{maxval}}{otherwise}\f]
    THRESH_TRUNC      = 2, //!< \f[\texttt{dst} (x,y) =  \fork{\texttt{threshold}}{if \(\texttt{src}(x,y) > \texttt{thresh}\)}{\texttt{src}(x,y)}{otherwise}\f]
    THRESH_TOZERO     = 3, //!< \f[\texttt{dst} (x,y) =  \fork{\texttt{src}(x,y)}{if \(\texttt{src}(x,y) > \texttt{thresh}\)}{0}{otherwise}\f]
    THRESH_TOZERO_INV = 4, //!< \f[\texttt{dst} (x,y) =  \fork{0}{if \(\texttt{src}(x,y) > \texttt{thresh}\)}{\texttt{src}(x,y)}{otherwise}\f]
    THRESH_MASK       = 7,
    THRESH_OTSU       = 8, //!< flag, use Otsu algorithm to choose the optimal threshold value
    THRESH_TRIANGLE   = 16 //!< flag, use Triangle algorithm to choose the optimal threshold value
};

cvthreshold.hpp

#include <QComboBox>
#include "opencv2/opencv.hpp"

Q_DECLARE_METATYPE(cv::ThresholdTypes)

class CVThresholdTypeComboBox : public QComboBox {
    Q_OBJECT
    Q_ENUM(cv::ThresholdTypes)
    Q_PROPERTY(cv::ThresholdTypes threshType READ threshType WRITE setThreshType USER true)
public:
    CVThresholdTypeComboBox(QWidget *widget = nullptr);
    cv::ThresholdTypes threshType() const;
    void setThreshType(const cv::ThresholdTypes &threshType);
private:
    void populateList();
};

cvthreshold.cpp

#include "cvthreshold.h"

CVThresholdTypeComboBox::CVThresholdTypeComboBox(QWidget *widget) : QComboBox(widget) {
    populateList();
}

cv::ThresholdTypes CVThresholdTypeComboBox::threshType() const {
    return qvariant_cast<cv::ThresholdTypes>(itemData(currentIndex(), qMetaTypeId<cv::ThresholdTypes>()));
}

void CVThresholdTypeComboBox::setThreshType(const cv::ThresholdTypes &threshType) {
    setCurrentIndex(findData(threshType, qMetaTypeId<cv::ThresholdTypes>()));
}

void CVThresholdTypeComboBox::populateList() {
    addItem("Binary",cv::THRESH_BINARY);
    addItem("Binary Inverted",cv::THRESH_BINARY_INV);
    addItem("Mask",cv::THRESH_MASK);
    addItem("Otsu",cv::THRESH_OTSU);
}

cvpipelineeditorwidget.cpp

#include "cvpipelineeditorwidget.h"
#include "ui_cvpipelineeditorwidget.h"
#include <QDebug>
#include <QComboBox>

#include <QItemEditorFactory>
#include "cvthreshold.h"

CVPipelineEditorWidget::CVPipelineEditorWidget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::CVPipelineEditorWidget) {
    ui->setupUi(this);
    setAttribute(Qt::WA_DeleteOnClose);

    ui->treeWidget->setHeaderLabels({"Enable","Eigenschaft","Wert"});
    ui->treeWidget->setColumnWidth(0, 50);

//TEST
    QItemEditorFactory * factory = new QItemEditorFactory;

    QItemEditorCreatorBase * threshTypeCreator =
        new QStandardItemEditorCreator<CVThresholdTypeComboBox>();

    factory->registerEditor(qMetaTypeId<cv::ThresholdTypes>(), threshTypeCreator);

    QItemEditorFactory::setDefaultFactory(factory);
//ENDTEST

    QTreeWidgetItem * item = new QTreeWidgetItem(ui->treeWidget);
    item->setCheckState(0, Qt::Checked);
    item->setText(1, "Threshold");
    QTreeWidgetItem * threshItem = new QTreeWidgetItem(item);
    threshItem->setText(1, "Threshold");
    threshItem->setData(2, Qt::DisplayRole, QStringList{"smtsmt","sad"});
    item->addChild(threshItem);
    QTreeWidgetItem * threshMaxItem = new QTreeWidgetItem(item);
    threshMaxItem->setText(1, "Maximum");
    item->addChild(threshMaxItem);
    QTreeWidgetItem * threshTypeItem = new QTreeWidgetItem(item);
    threshTypeItem->setText(1, "Algorithm");
    threshTypeItem->setData(2, Qt::DisplayRole, cv::THRESH_BINARY);
    QComboBox * threshTypeCombobox = new QComboBox;
    threshTypeCombobox->addItem("Binary",cv::THRESH_BINARY);
    threshTypeCombobox->addItem("Binary Inverted",cv::THRESH_BINARY_INV);
    threshTypeCombobox->addItem("Mask",cv::THRESH_MASK);
    threshTypeCombobox->addItem("Otsu",cv::THRESH_OTSU);
//    ui->treeWidget->setItemWidget(threshTypeItem, 2, threshTypeCombobox);

    QObject::connect(ui->treeWidget, &QTreeWidget::itemChanged, this, [this]{
        qDebug() << "Item data changed";
    });
}

No moc file being generated.

[Christian Ehrlicher]

@InTheBeninging said in QItemEditorCreatorBase with custom enum:

No moc file being generated

So what build system do you use? Without the moc file you will get this linker error

[Axel Spoerl]

@InTheBeninging said in QItemEditorCreatorBase with custom enum:

The enum is included from a seperate header file. Can I even use it as Q_ENUM in my own class?

That's not possible.
The Q_ENUM declaration has to be in the class where the enum is defined.
This class has to also have the Q_OBJECT macro, or (if the Q_OBJECT overhead is not needed, Q_GADGET).

[InTheBeninging]

Thanks for the hints @Christian-Ehrlicher and @Axel-Spoerl. I cleared my build folder before rebuilding and removed the Q_ENUM and it works now. The only problem is, that instead of showing the enums name the treewidgets cell remains empty after a selection as shown in the lower half of the image.

This is likely because Q_ENUM can't be used here. Is there any other way to add QString representations to custom MetaTypes?

[Axel Spoerl]

@InTheBeninging
As said already: Use the Q_OBJECT or Q_GADGETmacro. Or implement a manual conversion function.

[InTheBeninging]

Ok it works now. It just needed some changes.
I had to change the property function to save the data with the Qt::UserRole. I guess because the QComboBox::addItem(QString text, QVariant userData) function used to populate the box uses the Qt::UserRole by default.

cv::ThresholdTypes CVThresholdTypeComboBox::threshType() const {
    return qvariant_cast<cv::ThresholdTypes>(itemData(currentIndex(), Qt::UserRole));
}

void CVThresholdTypeComboBox::setThreshType(const cv::ThresholdTypes &threshType) {
    setCurrentIndex(findData(threshType, Qt::UserRole));
}

The conversion function to get a string representation of my custom metatype looks as follows.

QString CVThresholdTypeComboBox::thresholdToString(const cv::ThresholdTypes &threshType) {
    switch(threshType) {
    case cv::THRESH_BINARY:     return "Binary";
    case cv::THRESH_BINARY_INV: return "Binary Inverted";
    case cv::THRESH_TRUNC:      return "Truncated";
    case cv::THRESH_TOZERO:     return "To Zero";
    case cv::THRESH_TOZERO_INV: return "To Zero Inverted";
    case cv::THRESH_MASK:       return "Mask";
    case cv::THRESH_OTSU:       return "Otsu";
    case cv::THRESH_TRIANGLE:   return "Triangle";
    default:                    return "Default";
    }
}

The conversion function is registered with this function.

QMetaType::registerConverter<cv::ThresholdTypes, QString>(&CVThresholdTypeComboBox::thresholdToString);

[Axel Spoerl]

@InTheBeninging
Nice, good that you got it working.

Some minor beautification nits:

• text values could be stored in an array and the enum value be used as the index.
• the function could be static constexpr.
• in switches over enums, I don't use default. That way, the compiler rants at me, if I have (again!!) forgotten to implement new enum values.
  Q_UNREACHABLE()can be added after the switch, but it doesn't like static constexpron some platforms.