Unable to derive from QUndoCommand without "Class declaration lacks Q_OBJECT macro." Or alternatively many errors

enjoysmath

Here's my code for UndoCommands.h:

#ifndef UNDO_COMMANDS_CH
#define UNDO_COMMANDS_CH

#include <QUndoCommand>
#include <QString>

class UndoCommand : public QUndoCommand
{
public:
    void (*onTextChanged)(QString& str) = 0;

    UndoCommand(QUndoCommand* parent=0, bool skip1st=false)
        : QUndoCommand(parent)
    {
        m_skip1st = skip1st;     // means skip the first applied redo say if item pos already set
    }

    void setText(QString& text) {
        QUndoCommand::setText(text);
        if (onTextChanged)
            onTextChanged(text);
    }

    void redo() {
        if (m_skip1st) {
            m_skip1st = false;
        } else {
            redoImpl();
        }
    }

protected:
    virtual void redoImpl() = 0;

private:
    bool m_skip1st;
};

#include "GraphicsItem.h"

class DeleteGraphicsItem : public UndoCommand
{
public:
    DeleteGraphicsItem(GraphicsItem* item, QUndoCommand* parent=0)
        : UndoCommand(parent)
    {
        m_item = item;
    }

public slots:
    void redoImpl() {
        m_item->emitDeleted();
    }

    void undo() {
        m_item->emitUndeleted();
    }

private:
    GraphicsItem* m_item;
};

#endif // UNDO_COMMANDS_CH

When I include Q_OBJECT it results in these errors:

debug\moc_UndoCommands.cpp(71): error C2440: 'static_cast': cannot convert from 'QObject *' to 'DeleteGraphicsItem *'
debug\moc_UndoCommands.cpp(71): note: Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast
debug\moc_UndoCommands.cpp(83): error C2039: 'staticMetaObject': is not a member of 'UndoCommand'
c:\myprojects\___fruitful_approach\build-_zoomspace-desktop_qt_5_11_1_msvc2017_64bit-debug\debug\../../_ZOOMSPACE/UndoCommands.h(7): note: see declaration of 'UndoCommand'
debug\moc_UndoCommands.cpp(90): error C2227: left of '->metaObject' must point to class/struct/union/generic type
debug\moc_UndoCommands.cpp(90): error C2227: left of '->dynamicMetaObject' must point to class/struct/union/generic type
debug\moc_UndoCommands.cpp(98): error C2039: 'qt_metacast': is not a member of 'UndoCommand'
c:\myprojects\___fruitful_approach\build-_zoomspace-desktop_qt_5_11_1_msvc2017_64bit-debug\debug\../../_ZOOMSPACE/UndoCommands.h(7): note: see declaration of 'UndoCommand'
debug\moc_UndoCommands.cpp(103): error C2039: 'qt_metacall': is not a member of 'UndoCommand'
c:\myprojects\___fruitful_approach\build-_zoomspace-desktop_qt_5_11_1_msvc2017_64bit-debug\debug\../../_ZOOMSPACE/UndoCommands.h(7): note: see declaration of 'UndoCommand'
debug\moc_UndoCommands.cpp(108): error C2664: 'void DeleteGraphicsItem::qt_static_metacall(QObject *,QMetaObject::Call,int,void **)': cannot convert argument 1 from 'DeleteGraphicsItem *' to 'QObject *'
debug\moc_UndoCommands.cpp(108): note: Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast

So as you can see, I can't have custom undo commands? That's crap.

enjoysmath

I had redoImpl() in a protected area as well as in a public slot in the subclass. So it was coming up with those weird casting errors and Q_OBJECT complaints. Q_OBJECT I guess we don't use on QUndoCommand subclasses