Creating class from existing Qt class

Question

I've gone through the Qt 4.7 C++ tutorials and I've started a project to extend some of the functionality of QTreeView.

I'm attempting to do the following:

1. ensuring the program runs fine using QTreeView
2. copying and pasting new files based on ..\src\gui\itemviews\qtreeview.cpp, qtreeview.h, and qtreeview_p.h
3. replacing "QTreeView" to "CustomTreeView" in each filename and within each file (including the .pro file)

I am getting the following warnings (using MSVC, command-line):

.\CustomTreeView.cpp(147) : warning C4273: 'CustomTreeView::CustomTreeView' : inconsistent dll linkage
        c:\home\jetimms\code\projects\CustomTreeViewTest\CustomTreeView.hpp(31) : see previous definition of '{ctor}'

There are many more of these warnings, but they look the same as above.

Also, I have these errors:

.\CustomTreeView.cpp(1216) : error C2248: 'NoState' : cannot access protected enumerator declared in class 'QAbstractItemView'
    c:\qt\4.7.0\include\qtgui\../../src/gui/itemviews/qabstractitemview.h(304) : see declaration of 'NoState'
    c:\qt\4.7.0\include\qtgui\../../src/gui/itemviews/qabstractitemview.h(63) : see declaration of 'QAbstractItemView'
.\CustomTreeView.cpp(1216) : error C2248: 'EditingState' : cannot access protected enumerator declared in class 'QAbstractItemView'
    c:\qt\4.7.0\include\qtgui\../../src/gui/itemviews/qabstractitemview.h(307) : see declaration of 'EditingState'
    c:\qt\4.7.0\include\qtgui\../../src/gui/itemviews/qabstractitemview.h(63) : see declaration of 'QAbstractItemView'

The above is complaining about the equivalent of the following (in qtreeview.h) with no changes except replacing QTreeView with CustomTreeView:

bool QTreeViewPrivate::expandOrCollapseItemAtPos(const QPoint &pos)
{
    Q_Q(QTreeView);
    // we want to handle mousePress in EditingState (persistent editors)
    if ((state != QAbstractItemView::NoState
        && state != QAbstractItemView::EditingState)
        || !viewport->rect().contains(pos))
        return true;

    int i = itemDecorationAt(pos);
    if ((i != -1) && itemsExpandable && hasVisibleChildren(viewItems.at(i).index)) {
        if (viewItems.at(i).expanded)
            collapse(i, true);
        else
            expand(i, true);
        if (!isAnimating()) {
            q->updateGeometries();
            viewport->update();
        }
        return true;
    }
    return false;
}

I have included these new files in the .pro file in the SOURCES and HEADERS. I do not have extra versions of the constructor included as the above warning says.

updated: 20110710_0926

Here is the actual code that causes the errors:

bool CustomTreeViewPrivate::expandOrCollapseItemAtPos(const QPoint &pos) {
  Q_Q(CustomTreeView);
  // we want to handle mousePress in EditingState (persistent editors)
  if ((state != QAbstractItemView::NoState
        && state != QAbstractItemView::EditingState)
        || !viewport->rect().contains(pos))
    return true;

  int i = itemDecorationAt(pos);
  if ((i != -1) && itemsExpandable && hasVisibleChildren(viewItems.at(i).index)) {
    if (viewItems.at(i).expanded)
      collapse(i, true);
    else
      expand(i, true);
    if (!isAnimating()) {
      q->updateGeometries();
      viewport->update();
    }
    return true;
  }
  return false;
}

updated 20110710_1339:

When I attempted to compile (using qmake, as before) replacing my custom class with the qtreeview files in ..\src\gui\itemviews\, I received very similar warnings.

c:\Qt\4.7.0\src\gui\itemviews\qtreeview.cpp(187) : warning C4273: 'QTreeView::QTreeView' : inconsistent dll linkage
    c:\qt\4.7.0\src\gui\itemviews\qtreeview.h(74) : see previous definition

of '{ctor}'

There is only one error that appears with this try and it has to do with (moc_qtreeview.cpp which is compiled on the fly?):

C:\home\jetimms\code\projects\cashflow\debug\moc_qtreeview.cpp(95) : error C2491: 'QTreeView::staticMetaObject' : definition of dllimport static data member not allowed

Not sure if it tells me anything related to the cause of the warnings. Here is that snippit of code:

const QMetaObject QTreeView::staticMetaObject = {
    { &QAbstractItemView::staticMetaObject, qt_meta_stringdata_QTreeView,
      qt_meta_data_QTreeView, 0 }
};

I just find it strange that the QTreeView files themselves error out when I try to build with them.

Anyhow, the warning is telling me that the constructor for QTreeView has already been defined. I have guards on all of my header files, so there's nowhere that I can think of that it would think the QTreeView was defined twice.

updated: 20110710_1612

Here is the beginning of QTreeView.h with the definition of QTreeView. Note that it includes the QAbstractItemView.h and inherits from it.

#include <QtGui/qabstractitemview.h>
QT_BEGIN_HEADER
QT_BEGIN_NAMESPACE
QT_MODULE(Gui)
#ifndef QT_NO_TREEVIEW
class QTreeViewPrivate;
class QHeaderView;
class Q_GUI_EXPORT QTreeView : public QAbstractItemView
{
  ...

In exactly the same way, my custom class inherits from it.

#include <QtGui/qabstractitemview.h>
QT_BEGIN_HEADER
QT_BEGIN_NAMESPACE
QT_MODULE(Gui)
#ifndef QT_NO_TREEVIEW
class CustomTreeViewPrivate;
class QHeaderView;
class Q_GUI_EXPORT CustomTreeView : public QAbstractItemView
{

updated: 20110710_1757

It dawned on me that the code I was copying from QTreeView is for a library and I am not building a library, just the .exe for my app. I removed the Q_GUI_EXPORT from the constructor (just above) and the warnings I was experiencing were gone.

Now I am getting an error dealing with the moc_CustomTreeView.cpp file (there are 3 errors in all, all like this one):

debug\moc_CustomTreeView.cpp(140) : error C2027: use of undefined type 'CustomTreeViewPrivate'
        c:\home\jetimms\code\projects\cashflow\debug\../CustomTreeView.hpp(12) : see declaration of 'CustomTreeViewPrivate'
debug\moc_CustomTreeView.cpp(140) : error C2227: left of '->_q_endAnimatedOperation' must point to class/struct/union/generic type

Here's the offending code:

    case 16: d_func()->_q_endAnimatedOperation(); break;

Not sure what to do about the moc_ file errors. d_func() grabs the CustomTreeViewPrivate instance, but the moc_ file scope can't see it.

updated: 20110710_1757

I looked around to understand moc_ files and the Qt way of development and found these two. KDE Techbase Policies/Library Code Policy This one explains why the Qt code is written as it is, using private classes and such.

I also found the following page that explains what to do when your moc_ code gives you errors like the ones I have above (rerun qmake), Using the Meta-Object Compiler (moc). I tried this and the above moc_ errors went away and now I am presented with these.

Bye the way, I changed the CustomTreeView name to SummaryDrillDownTreeView2.

SummaryDrillDownTreeView2.obj : error LNK2019: unresolved external symbol "public: virtual __thiscall QAbstractItemViewPrivate::~QAbstractItemViewPrivate(void)" (??1QAbstractItemViewPrivate@@UAE@XZ) referenced in function __unwindfunclet$??0SummaryDrillDownTreeView2Private@@QAE@XZ$0
SummaryDrillDownTreeView2.obj : error LNK2019: unresolved external symbol "public: __thiscall QAbstractItemViewPrivate::QAbstractItemViewPrivate(void)" (??0QAbstractItemViewPrivate@@QAE@XZ) referenced in function "public: __thiscall SummaryDrillDownTreeView2Private::SummaryDrillDownTreeView2Private(void)" (??0SummaryDrillDownTreeView2Private@@QAE@XZ)
SummaryDrillDownTreeView2.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall QAbstractItemViewPrivate::_q_rowsRemoved(class QModelIndex const &,int,int)" (?_q_rowsRemoved@QAbstractItemViewPrivate@@UAEXABVQModelIndex@@HH@Z)
SummaryDrillDownTreeView2.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall QAbstractItemViewPrivate::_q_columnsInserted(class QModelIndex const &,int,int)" (?_q_columnsInserted@QAbstractItemViewPrivate@@UAEXABVQModelIndex@@HH@Z)
SummaryDrillDownTreeView2.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall QAbstractItemViewPrivate::_q_layoutChanged(void)" (?_q_layoutChanged@QAbstractItemViewPrivate@@UAEXXZ)
SummaryDrillDownTreeView2.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall QAbstractItemViewPrivate::selectAll(class QFlags<enum QItemSelectionModel::SelectionFlag>)" (?selectAll@QAbstractItemViewPrivate@@UAEXV?$QFlags@W4SelectionFlag@QItemSelectionModel@@@@@Z)
SummaryDrillDownTreeView2.obj : error LNK2001: unresolved external symbol "public: virtual enum QAbstractItemView::DropIndicatorPosition __thiscall QAbstractItemViewPrivate::position(class QPoint const &,class QRect const &,class QModelIndex const &)const " (?position@QAbstractItemViewPrivate@@UBE?AW4DropIndicatorPosition@QAbstractItemView@@ABVQPoint@@ABVQRect@@ABVQModelIndex@@@Z)
SummaryDrillDownTreeView2.obj : error LNK2019: unresolved external symbol "public: void __thiscall QAbstractItemViewPrivate::doDelayedItemsLayout(int)" (?doDelayedItemsLayout@QAbstractItemViewPrivate@@QAEXH@Z) referenced in function "public: void __thiscall SummaryDrillDownTreeView2::setRowHidden(int,class QModelIndex const &,bool)" (?setRowHidden@SummaryDrillDownTreeView2@@QAEXHABVQModelIndex@@_N@Z)
SummaryDrillDownTreeView2.obj : error LNK2019: unresolved external symbol "public: void __thiscall QAbstractItemViewPrivate::interruptDelayedItemsLayout(void)const " (?interruptDelayedItemsLayout@QAbstractItemViewPrivate@@QBEXXZ) referenced in function "public: void __thiscall SummaryDrillDownTreeView2::expandAll(void)" (?expandAll@SummaryDrillDownTreeView2@@QAEXXZ)
SummaryDrillDownTreeView2.obj : error LNK2019: unresolved external symbol "public: virtual void __thiscall QAbstractItemViewPrivate::_q_modelDestroyed(void)" (?_q_modelDestroyed@QAbstractItemViewPrivate@@UAEXXZ) referenced in function "public: virtual void __thiscall SummaryDrillDownTreeView2Private::_q_modelDestroyed(void)" (?_q_modelDestroyed@SummaryDrillDownTreeView2Private@@UAEXXZ)
SummaryDrillDownTreeView2.obj : error LNK2019: unresolved external symbol "public: virtual class QList<struct QPair<class QRect,class QModelIndex> > __thiscall QAbstractItemViewPrivate::draggablePaintPairs(class QList<class QModelIndex> const &,class QRect *)const " (?draggablePaintPairs@QAbstractItemViewPrivate@@UBE?AV?$QList@U?$QPair@VQRect@@VQModelIndex@@@@@@ABV?$QList@VQModelIndex@@@@PAVQRect@@@Z) referenced in function "public: virtual class QList<struct QPair<class QRect,class QModelIndex> > __thiscall SummaryDrillDownTreeView2Private::draggablePaintPairs(class QList<class QModelIndex> const &,class QRect *)const " (?draggablePaintPairs@SummaryDrillDownTreeView2Private@@UBE?AV?$QList@U?$QPair@VQRect@@VQModelIndex@@@@@@ABV?$QList@VQModelIndex@@@@PAVQRect@@@Z)
SummaryDrillDownTreeView2.obj : error LNK2019: unresolved external symbol "public: class QStyleOptionViewItemV4 __thiscall QAbstractItemViewPrivate::viewOptionsV4(void)const " (?viewOptionsV4@QAbstractItemViewPrivate@@QBE?AVQStyleOptionViewItemV4@@XZ) referenced in function "protected: void __thiscall SummaryDrillDownTreeView2::drawTree(class QPainter *,class QRegion const &)const " (?drawTree@SummaryDrillDownTreeView2@@IBEXPAVQPainter@@ABVQRegion@@@Z)
SummaryDrillDownTreeView2.obj : error LNK2019: unresolved external symbol "public: struct QEditorInfo __thiscall QAbstractItemViewPrivate::editorForIndex(class QModelIndex const &)const " (?editorForIndex@QAbstractItemViewPrivate@@QBE?AUQEditorInfo@@ABVQModelIndex@@@Z) referenced in function "protected: virtual void __thiscall SummaryDrillDownTreeView2::drawRow(class QPainter *,class QStyleOptionViewItem const &,class QModelIndex const &)const " (?drawRow@SummaryDrillDownTreeView2@@MBEXPAVQPainter@@ABVQStyleOptionViewItem@@ABVQModelIndex@@@Z)
SummaryDrillDownTreeView2.obj : error LNK2019: unresolved external symbol "public: void __thiscall QFramePrivate::updateStyledFrameWidths(void)" (?updateStyledFrameWidths@QFramePrivate@@QAEXXZ) referenced in function "public: void __thiscall SummaryDrillDownTreeView2Private::initialize(void)" (?initialize@SummaryDrillDownTreeView2Private@@QAEXXZ)
SummaryDrillDownTreeView2.obj : error LNK2019: unresolved external symbol "public: virtual void __thiscall QAbstractItemViewPrivate::_q_columnsAboutToBeRemoved(class QModelIndex const &,int,int)" (?_q_columnsAboutToBeRemoved@QAbstractItemViewPrivate@@UAEXABVQModelIndex@@HH@Z) referenced in function "public: virtual void __thiscall SummaryDrillDownTreeView2Private::_q_columnsAboutToBeRemoved(class QModelIndex const &,int,int)" (?_q_columnsAboutToBeRemoved@SummaryDrillDownTreeView2Private@@UAEXABVQModelIndex@@HH@Z)
SummaryDrillDownTreeView2.obj : error LNK2019: unresolved external symbol "public: virtual void __thiscall QAbstractItemViewPrivate::_q_columnsRemoved(class QModelIndex const &,int,int)" (?_q_columnsRemoved@QAbstractItemViewPrivate@@UAEXABVQModelIndex@@HH@Z) referenced in function "public: virtual void __thiscall SummaryDrillDownTreeView2Private::_q_columnsRemoved(class QModelIndex const &,int,int)" (?_q_columnsRemoved@SummaryDrillDownTreeView2Private@@UAEXABVQModelIndex@@HH@Z)
debug\cashflow.exe : fatal error LNK1120: 16 unresolved externals

Answer 1

I can’t really say about MSVC, but those members are declared as protected for QAbstractTreeView, like the error says. You didn’t paste source related to errors, but I guess you are trying to use those protected members somehow that does not qualify as sub-class usage, maybe by doing an instance and using that?

EDIT:

if ((state != QAbstractItemView::NoState

This is the actual line that is causing the error. Here you are using a protected member of QAbstractView, which is not allowed, as protected members are purely allowed to use for subclasses.

If you class inherited the QAbstractView, you could use that member.

Answer 2

You should use inheritance to create the new class, rather than copy and paste. Less code to maintain that way, and less likely to break with even minor Qt upgrades.