ListView undefined reference to vtable for Custom Delegate (QStyledItemDelegate)

CybeX · 12 Nov 2017, 08:17

Good day

I required a QListView to display information in a readable fashion to a user. After much searching, I came across this post made in 2010.

What I tried:
Following the code provided had me creating a custom delegate, a QStyledItemDelegate.

A delegate is required to allow a developer to 'customize' how they want data to be displayed. e.g. Display 2 icons on a ListView item/entry with text inbetween.

Using this understanding which I derived from the paint() and sizeHint() methods, I proceeded to edit it for my own use. See below for code example.

The Problem:

The issue I have is simple. Undefined reference to 'vtable for ServerDelegate'.

serverdelegate.o: In function `ServerDelegate::ServerDelegate()':
/../../../serverdelegate.cpp:3: undefined reference to `vtable for ServerDelegate'
collect2: error: ld returned 1 exit status
make: *** [Makefile:291: VPNSumo] Error 1
09:32:22: The process "/usr/bin/make" exited with code 2.
Error while building/deploying project VPNSumo (kit: Desktop Qt 5.9.3 GCC 64bit)
When executing step "Make"

Out of experience (and lots of Google'ing), I have found that this is very often a case where the Q_OBJECT macro is not defined/declared in the header file, since methods defined in the Q_OBJECT macro are used within this class.

See for reference:

What I tried v2

I then proceeded to append the Q_OBJECT macro to the ServerDelegate class, also adding a constructor argument to the ServerDelegate constructor:

ServerDelegate(QStyledItemDelegate* parent = 0);

and implemented by:

ServerDelegate::ServerDelegate(QStyledItemDelegate *parent)
    : QStyledItemDelegate(parent)
{
//...
}

but the error persisted. I added a default constructor as a last resort taking no arguments, and as expected, it also did not work.

Error after adding parent argument and default constructor:

serverdelegate.o: In function `ServerDelegate::ServerDelegate()':
/../../../serverdelegate.cpp:3: undefined reference to `vtable for ServerDelegate'
serverdelegate.o: In function `ServerDelegate::ServerDelegate(QStyledItemDelegate*)':
/../../../serverdelegate.cpp:15: undefined reference to `vtable for ServerDelegate'
collect2: error: ld returned 1 exit status
make: *** [Makefile:291: VPNSumo] Error 1
09:40:52: The process "/usr/bin/make" exited with code 2.
Error while building/deploying project VPNSumo (kit: Desktop Qt 5.9.3 GCC 64bit)
When executing step "Make"

I am out of ideas, and at Google Results page 5

Help would be very much appreciated

Code for class ServerDelegate

ServerDelegate.h

#ifndef SERVERDELEGATE_H
#define SERVERDELEGATE_H

#include <QApplication>
#include <QtGui>
#include <QStyledItemDelegate>
#include <QtWidgets>

class ServerDelegate : public QStyledItemDelegate
{

public:
    ServerDelegate();
    virtual ~ServerDelegate();

    enum DataRole{
        CountryText = Qt::UserRole + 100,
        CityText = Qt::UserRole+101,
        CountryFlag = Qt::UserRole+102,
        PremiumFlag = Qt::UserRole+103,
        ListIndex = Qt::UserRole+104
    };

    void paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const;

    QSize sizeHint(const QStyleOptionViewItem &option, const QModelIndex &index) const;

private:
    QFont fontCountry, fontCity;
};

#endif // SERVERDELEGATE_H

and the implementation serverdelegate.cpp

**Please note: the implementation is untested due to the error below

#include "serverdelegate.h"

ServerDelegate::ServerDelegate()
{
    fontCountry = QApplication::font();
    fontCountry.setBold(true);
    fontCountry.setPointSize(QApplication::font().pointSize() + 3);

    fontCity = QApplication::font();
    fontCity.setItalic(true);
    fontCity.setPointSize(QApplication::font().pointSize() - 1);
}

QSize ServerDelegate::sizeHint(const QStyleOptionViewItem &option, const QModelIndex &index) const{
    QIcon countryFlag = qvariant_cast<QIcon>(index.data(CountryFlag));
    QIcon premiumFlag = qvariant_cast<QIcon>(index.data(PremiumFlag));

    QSize totalCountrySize = countryFlag.actualSize(option.decorationSize);
    QSize totalPremiumSize = premiumFlag.actualSize(option.decorationSize);

    QFontMetrics fmCountry(fontCountry);
    QFontMetrics fmCity(fontCity);

    int fontHeight = 4 + fmCountry.height() + 2 + fmCity.height() + 4;
    int iconHeight = 4 + (totalCountrySize.height() > totalPremiumSize.height() ? totalCountrySize.height() : totalPremiumSize.height()) + 4;

    return QSize(totalCountrySize.width() + totalPremiumSize.width(), (fontHeight > iconHeight ? fontHeight : iconHeight));
}

void ServerDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const{
    QStyledItemDelegate::paint(painter, option, index);
    painter->save();


    QString countryText = index.data(DataRole::CountryText).toString();
    QString cityText = index.data(DataRole::CityText).toString();
    QFontMetrics fmCountry(fontCountry);
    QFontMetrics fmCity(fontCity);

    QPixmap cF, pF;
    cF.loadFromData(index.data(DataRole::CountryFlag).toByteArray(), "PNG");
    pF.loadFromData(index.data(DataRole::PremiumFlag).toByteArray(), "PNG");
    QIcon countryFlag = QIcon(cF);
    QIcon premiumFlag = QIcon(pF);
    QSize totalCountrySize = countryFlag.actualSize(option.decorationSize);
    QSize totalPremiumSize = premiumFlag.actualSize(option.decorationSize);

    QRect rectSeperator = option.rect;
    QRect rectCountryText = option.rect;
    QRect rectCityText = option.rect;
    QRect rectCountryFlag = option.rect;
    QRect rectPremiumFlag = option.rect;

    rectSeperator.setTop(0);
    rectSeperator.setLeft(0);
    rectSeperator.setBottom(2);
    rectSeperator.setRight(option.rect.width());

    rectCountryFlag.setRight(totalCountrySize.width()+20);
    rectCountryFlag.setTop(totalCountrySize.height()+4);

    rectCountryText.setLeft(rectCountryFlag.right());
    rectCountryText.setTop(fmCountry.height()+4);

    rectCityText.setLeft(rectCountryFlag.right());
    rectCityText.setTop(fmCity.height()+2);

    rectPremiumFlag.setLeft(rectCountryFlag.right());
    rectCountryFlag.setTop(totalCountrySize.height());


    painter->drawRect(rectSeperator);
    painter->drawPixmap(QPoint(rectCountryFlag.left()+totalCountrySize.width()/2+2,rectCountryFlag.top()+totalCountrySize.height()/2+3),countryFlag.pixmap(totalCountrySize.width(),totalCountrySize.height()));
    painter->setFont(fontCountry);
    painter->drawText(rectCountryText, countryText);
    painter->setFont(fontCity);
    painter->drawText(rectCityText, cityText);
    painter->drawPixmap(QPoint(rectPremiumFlag.left()+totalPremiumSize.width()/2+2,rectPremiumFlag.top()+totalPremiumSize.height()/2+3),premiumFlag.pixmap(totalPremiumSize.width(),totalPremiumSize.height()));
    painter->restore();
}

Update v1

According to a suggestion on StackOverflow, it was mentioned that I did not Run qMake after adding the macro. I did so, resulting in further errors. I took the following steps when I built the application:

clean
run qmake
rebuild

The resulting error indicates and issue with the moc* output. To my knowledge, this results from an old build with classes not all including the required macros.

However, this error points to the virtual destructor of the ServerDelegate class.

In the tutorial I followed, it required one to create the virtual destructor to allow the parent to handle deleting the object.

and here is the error output:

moc_serverdelegate.o:(.data.rel.ro._ZTV14ServerDelegate[_ZTV14ServerDelegate]+0x28): undefined reference to `ServerDelegate::~ServerDelegate()'
moc_serverdelegate.o:(.data.rel.ro._ZTV14ServerDelegate[_ZTV14ServerDelegate]+0x30): undefined reference to `ServerDelegate::~ServerDelegate()'
collect2: error: ld returned 1 exit status
make: *** [Makefile:293: VPNSumo] Error 1
10:09:41: The process "/usr/bin/make" exited with code 2.
Error while building/deploying project VPNSumo (kit: Desktop Qt 5.9.3 GCC 64bit)
When executing step "Make"

CybeX · 11 Dec 2017, 08:48

It turns out that all that was required is an implementation for the ~virtual() method. A bare implementation of the destructor is required.

VRonin · wrote on 11 Dec 2017, 08:22

you have to just combine the 2 solutions you already have.
Add Q_OBJECT (good thing to have the QObject* parent =Q_NULLPTR constructor too) and re-run qmake

CybeX · 11 Dec 2017, 08:48

It turns out that all that was required is an implementation for the ~virtual() method. A bare implementation of the destructor is required.

VRonin · C CybeX 11 Dec 2017, 08:45

Actually, since the base class already has a virtual destructor you can just remove the destructor of your derived altogether